Rodents as Pollinators

Leucospermum arenarium in the field and one of its pollinators, Gerbillurus paeba, feeding on flowers. (A) Pollen presenter contact on G. paeba. (B) G. paeba foraging on L. arenarium [Source]

It may come as a surprise to some that small mammals such as rodents, shrews, and even marsupials have been coopted by plants for pollination services. Far from being occasional evolutionary oddities, many plants have coopted small furry critters for their reproductive needs. Some of the best illustrations of this phenomenon occur in the Protea family (Proteaceae).

Protea nana. Photo by SAplants licensed under CC BY-SA 4.0

The various members of Proteaceae are probably best known for their bizarre floral displays. Indeed, they are most often encountered outside of their native habitats as outlandish additions to the cut flower industry. Superficial interest in beauty aside, the floral structure of the various protea genera and species is complex to say the least. They are well adapted to ensure cross pollination regardless of what the inflorescence attracts. Most notable is the fact that pollen doesn’t stay on the anthers. Instead, it is deposited on the tip of a highly modified style, which is referred to as the pollen presenter. Usually these structures remain closed until some visiting animal triggers their release.

The inconspicuous floral display of Protea cordata. Photo by SAplants licensed under CC BY-SA 4.0

Although birds and insects have taken up a majority of the pollination needs of this family, small mammals have entered into the equation on multiple occasions. Pollination by rodents, shrews, and marsupials is collectively referred to as therophilly and it appears to be quite a successful strategy at that. Therophilous pollination has arisen in more than one genera within Proteaceae.

A therophilous pollination syndrome appears to come complete with a host of unique morphological characters aimed at keeping valuable pollen and nectar away from birds and insects. The inflorescences of therophilous species like Protea nana, P. cordata, and Leucospermum arenarium are usually tucked deep inside the branches of these bushes, often at or near ground level. They are also quite robust and sturdy in nature, which is thought to be an adaptation to avoid damage incurred by the teeth of hungry mammals. The inflorescences of therophilous proteas also tend to have brightly colored or even shiny flowers surrounded by inconspicuous brown involucral bracts.

(C) Flowering L. arenarium with dense, mat-forming inflorescences. (D) Geoflorous inflorescences. (E) Pendulous inflorescences above ground level. [Source]

Contrasted against bird pollinated proteas, these inflorescences can seem rather drab but that is because small mammals like rodents and shrews are drawn in by another sense - smell. Therophilous proteas tend to produce inflorescences with strong musty or yeasty odors. They also produce copious amounts of sugar-rich, syrupy nectar. Small mammals, after all, need to take in a lot of calories throughout their waking hours and it appears that proteas use that to their advantage.

A small mouse pollinating Protea nana

As a rodent or shrew slinks in to take a drink, its head gets completely covered in pollen. In fact, they become so dusted with pollen that, before small, easy to hide trail cameras became affordable, pollen loads in the feces of rodents were the main clue that these plants were attracting something other than birds or insects. What’s more, the flowering period of many of these therophilous proteas occurs in the spring, right around the time when many small mammals go into breeding mode. Its during this time that small mammals need all of the energy they can get.

As odd as it may seem, rodent pollination appears to be a successful strategy for a considerable amount of protea species. The proteas aren’t alone either. Other plants appear to have evolved therophilous pollination as well. Nature, after all, works with what it has available and small mammals like rodents make up a considerable portion of regional faunas. With that in mind, it is no wonder that more plants have not converged on a similar strategy. Likely many have, we just need to take the time to sit down and observe.

Photo Credits: [1] [2] [3] [4] [5] [6] [7]

Further Reading: [1] [2] [3] [4] [5]

Glacier Mice

Photograph by Dr. Darrel Swift/Univeristy of Sheffield

At first glance the surface of a glacier hardly seems hospitable. Cold, barren, and windswept, glaciers appear to be the antithesis of life. However, this assumption is completely completely false. Glaciers are home to an interesting ecosystem of their own, albeit on a smaller scale than we normally give attention to.

From pockets of water on the surface to literal lakes of water sealed away inside, glaciers are home to a myriad microbial life. On some glaciers the life even gets a bit larger. Glaciers are littered with debris. As dust and gravel accumulate on the surface of the ice, they begin to warm ever so slightly more than the frozen water around them. Because of this, they are readily colonized by mosses such as those in the genus Racomitrium.

The biggest challenge to moss colonizers is the fact that glaciers are constantly moving, which anymore today means shrinking. As such, these bits of debris, along with the mosses growing on them, do not sit still as they would in say a forest setting. Instead they roll around. As the moss grows it spreads across the surface of the rock while the ice rotates it around. This causes the moss to grow on top of itself, inevitably forming a ball-like structure affectionately referred to as a "glacier mouse."

Because the moss stays ever so slightly warmer than its immediate surroundings, glacier mice soon find themselves teaming with life. Everything from worms to springtails and even a few water bears call glacier mice home. In a study recently published in Polar Biology, researcher Dr. Steve Coulson found "73 springtails, 200 tardigrades and 1,000 nematodes" thriving in just a single mouse!

The presence of such a diverse community living in these little moss balls brings up an important question - how do these animals find themselves in the glacier mice in the first place? After all, life just outside of the mouse is very brutal. As it turns out, the answer to this can be chalked up to how the mice form in the first place. As they blow and roll around the the surface of the glacier, they will often bump into one another and even collect in nooks and crannies together. It is believed that as this happens, the organisms living within migrate from mouse to mouse. The picture being painted here is that far from being a sterile environment, glaciers are proving to be yet another habitat where life prospers. Sadly, as climate change causes glaciers retreat at an ever increasing rate, glacier mice and all of the life they support will lose the very conditions they rely on for survival.

Photo Credit: [1] [2]

Further Reading: [1]

A Very Strange Maple

Photo by Abrahami licensed under CC BY-SA 2.5

I love being humbled by plant ID. Confusion usually means I am going to end up learning something new. This happened quite recently during a trip through The Morton Arboretum. Admittedly trees are not my forte but I had spotted something that seemed off and needed further inspection. I was greeted by a small tree with leaves that screamed "birch family" (Betulaceae) yet they were opposite. Members of the birch family should have alternately arranged leaves. What the heck was I looking at?

It didn't take long for me to find the ID tag. As a plant obsessed person, the information on the tag gave me quite the thrill. What I was looking at was possible the strangest maple on the planet. This, my friends, was my first introduction to Acer carpinifolium a.k.a the hornbeam maple.

Photo (c)2006 Derek Ramsey (Ram-Man) licensed under CC BY-SA 2.5

The hornbeam maple is endemic to Japan where it can be found growing in mountainous woodlands and alongside streams. Maxing out around 30 feet (9 m) in height, the hornbeam maple is by no means a large tree. It would appear that it has a similar place in its native ecology as other smaller understory maples do here in North America. It blooms in spring and its fruits are the typical samaras one comes to expect from the genus.

It probably goes without saying that the thing I find most fascinating about the hornbeam maple are its leaves. As both its common and scientific names tell you, they more closely resemble that of a hornbeam (Carpinus spp.) than a maple. Unlike the lobed, palmately veined leaves of its cousins, the hornbeam maple produces simple, unlobed leaves with pinnate venation and serrated margins. They challenge everything I have come to expect out of a maple. Indeed, the hornbeam maple is one of only a handful of species in the genus Acer that break the mold for leaf shape. However, compared to the rest, I think its safe to say that the hornbeam maple is the most aberrant of them all. 

Photo by Qwert1234 licensed under CC BY-SA 3.0

Not a lot of phylogenetic work has been done on the relationship between the hornbeam maple and the rest of its Acer cousins. At least one study suggests that it is most closely related to the mountain maple of neartheastern North America. More scrutiny will be needed before anyone can make this claim with certainty. Still, from an anecdotal standpoint, it seems like a reasonable leap to make considering just how shallow the lobes are on mountain maple leaves.

Regardless of who it is related to, running into this tree was truly a thrilling experience. I love it when species challenge long held expectations of large groups of plants. Hornbeam maple has gone from a place of complete mystery to me to being one of my favorite maples of all time. I hope you too will get a chance to meet this species if you haven't already!

Photo Credits: [1] [2] [3]

Further Reading: [1] [2]

Getting to Know Sansevieria

Photo by Mokkie licensed under CC BY-SA 3.0

The houseplant hobby is experiencing something of a renaissance as of late. With their popularity on various social media platforms, easy to grow plant species and their cultivars are experiencing a level of popularity they haven't seen in decades. One genus of particular interest to houseplant hobbyists is Sansevieria.

Despite their popularity, the few Sansevieria species regularly found in cultivation come attached with less than appealing common names. Mother-in-law's tongue, Devil's tongue, and snake plant all carry with them an air of negativity for what are essentially some of the most forgiving houseplants on the market. What few houseplant growers realize is that those dense clumps of upright striped leaves tucked into a dark corner of their home belong to a fascinating genus worthy of our admiration. What follows is a brief introduction to these enigmatic houseplants.

Sansevieria cylindrica. Photo by Marlon Machado licensed under CC BY-NC 2.0

Sansevieria ballyi. Photo by jurosig licensed under CC BY-NC-SA 2.0

The Sansevieria we encounter in most nurseries are just the tip of the iceberg. Sansevieria is a genus comprised of about 70 different species. I say 'about' because this group is a taxonomic mess. There are a couple reasons for this. For starters, the vast majority of Sansevieria species are painfully slow growers. It can take decades for an individual to reach maturity. As such, they have never really presented nursery owners with much in the way of economic gain and thus only a few have received any commercial attention.

Another reason has to do with the fiber market during and after World War II. In hopes of discovering new plant-based fibers for rope and netting, the USDA collected many Sansevieria but never formally described most of them. Instead, plants were assigned numbers in hopes that future botanists would take the time needed to parse them out properly.

A third reason has to do with the variety of forms and colors these plants can take. Horticulturists have been fond of giving plants their own special cultivar names. This complicates matters as it is hard to say which names apply to which species. Often the same species can have different names depending on who popularized it and when.

Sansevieria grandis in situ. Photo by Ton Rulkens licensed under CC BY-SA 2.0

Regardless of what we call them, all Sansevieria hail from arid regions of Africa, Madagascar and southern Asia. In the wild, many species resemble agave or yucca and, indeed, they occupy similar niches to these New World groups. Like so many other plants of arid regions, Sansevieria evolved CAM photosynthesis as a means of coping with heat and drought. Instead of opening up their stomata during the day when high temperatures would cause them to lose precious water, they open them at night and store CO2 in the form of an organic acid. When the sun rises the next day, the plants close up their stomata and utilize the acid-stored carbon for their photosynthetic needs.

The wonderfully compact Sansevieria pinguicula. Photo by Peter A. Mansfeld licensed under CC BY 3.0

Often you will encounter clumps of Sansevieria growing under the dappled shade of a larger tree or shrub. Some even make it into forest habitats. Most if not all species are long lived plants, living multiple decades under the right conditions. These are just some of the reasons that they make such hardy houseplants.

The various Sansevieria appear to sort themselves out along a handful of different growth forms. The most familiar to your average houseplant enthusiast is the form typified by Sansevieria trifasciata. These plants produce long, narrow, sword shaped leaves that point directly towards the sky. Many other Sansevieria species, such as S. subspicata and S. ballyi, take on a more rosetted form with leaves that span the gamut from thin to extremely succulent. Still others, like S. grandis and S. forskaalii, produce much larger, flattened leaves that grow in a form reminiscent of a leaky vase. 

Sansevieria trifasciata with berries. Photo by Mokkie licensed under CC BY-SA 3.0

Regardless of their growth form, a majority of Sansevieria species undergo radical transformations as they age. Because of this, adults and juveniles can look markedly different from one another, a fact that I suspect lends to some of the taxonomic confusion mentioned earlier. A species that illustrates this nicely is S. fischeri. When young, S. fischeri consists of tight rosettes of thick, mottled leaves. For years these plants continue to grow like this, reaching surprisingly large sizes. Then the plants hit maturity. At that point, the plant switches from its rosette form to producing single leaves that protrude straight out of the ground and can reach heights of several feet! Because the rosettes eventually rot away, there is often no sign of the plants previous form.

A mature Sansevieria fischeri with its large, upright, cylindrical leaves. Photo by Peter A. Mansfeld licensed under CC BY 3.0

If patient, many of the Sansevieria will reach enormous sizes. Such sizes are rarely observed as slow growth rates and poor housing conditions hamper their performance. It's probably okay too, considering the fact that, when fully grown, such specimens would be extremely difficult to manage in a home. If you are lucky, however, your plants may flower. And flower they do!

Though there is variation among the various species, Sansevieria all form flowers on either a simple or branched raceme. Flowers range in color from greenish white to nearly brown and all produce a copious amount of nectar. I have even noticed sickeningly sweet odors emanating from the flowers of some captive specimens. After pollination, flowers give way to brightly colored berries, hinting at their place in the family Asparagaceae.

A flowering Sansevieria hallii. Photo by Ton Rulkens licensed under CC BY-SA 2.0

As a whole, Sansevieria can be seen as exceptional tolerators, eking out an existence wherever the right microclimate presents itself in an otherwise harsh landscape. Their extreme water efficiency, tolerance of shade, and long lived habit has lent to the global popularity of only a few species. For the majority of the 70 or so species in this genus, their painfully slow growth rates means that they have never made quite a splash in the horticulture trade.

Nonetheless, Sansevieria is one genus that even the non-botanically minded among us can pick out of a lineup. Their popularity as houseplants may wax and wane but plants like S. trifasciata are here to stay. My hope is that all of these folks collecting houseplants right now will want to learn more about the plants they bring into their homes. They are more than just fancy decorations, they are living things, each with their own story to tell. 

NOTE: Since writing this article, I have learned that the genus Sansevieria has been lumped into the genus Dracaena. For the sake of familiarity, I retain the generic name Sansevieria for this article.

Photo Credits: [1] [2] [3] [4] [5] [6] [7] [8]

Further Reading: [1] [2] [3]

Maples, Epiphytes, and a Canopy Full of Goodies

The forests of the Pacific Northwest are known for the grandeur. This region is home to one of the greatest temperate rainforests in the world. A hiker is both dwarfed and enveloped by greenery as soon as they hit the trail. One aspect of these forests that is readily apparent are the carpets of epiphytes that drape limbs and branches all the way up into the canopy. Their arboreal lifestyle is made possible by a combination of mild winters and plenty of precipitation. 

We are frequently taught that the relationship between trees and their epiphytes are commensal - the epiphytes get a place to live and the trees are no worse for wear. However, there are a handful of trees native to the Pacific Northwest that are changing the way we think about the relationship between these organisms in temperate rainforests.

Though conifers dominate the Pacific Northwest landscape, plenty of broad leaved tree species abound. One of the most easily recognizable is the bigleaf maple (Acer macrophyllum). Both its common and scientific names hint at its most distinguishing feature, its large leaves. Another striking feature of this tree are its epiphyte communities. Indeed, along with the vine maple (A. circinatum), these two tree species carry the greatest epiphyte to shoot biomass ratio in the entire forest. Numerous species of moss, liverworts, lichens, and ferns have been found growing on the bark and branches of these two species.

Epiphyte loads are pretty intense. One study found that the average epiphyte crop of a bigleaf maple weighs around 78 lbs. (35.5 Kg). That is a lot of biomass living in the canopy! The trees seem just fine despite all of that extra weight. In fact, the relationship between bigleaf and vine maples and their epiphyte communities run far deeper than commensalism. Evidence accumulated over the last few decades has revealed that these maples are benefiting greatly from their epiphytic adornments.

Rainforests, both tropical and temperate, generally grow on poor soils. Lots of rain and plenty of biodiversity means that soils are quickly leached of valuable nutrients. Any boost a plant can get from its environment will have serious benefits for growth and survival. This is where the epiphytes come in. The richly textured mix of epiphytic plants greatly increase the surface area of any branch they live on. And all of that added surface area equates to more nooks and crannies for water and dust to get caught and accumulate.

Photo by SuperFantastic licensed under CC BY 2.0

When researchers investigated just how much of a nutrient load gets incorporated into these epiphyte communities, the results painted quite an impressive picture. On a single bigleaf maple, epiphyte leaf biomass was 4 times that of the host tree despite comprising less than 2% of the tree's above ground weight. All of that biomass equates to a massive canopy nutrient pool rich in nitrogen, phosphorus, potassium, calcium, magnesium, and sodium. Much of these nutrients arrive in the form of dust-sized soil particles blowing around on the breeze. What's more, epiphytes act like sponges, soaking up and holding onto precious water well into the dry summer months.

Now its reasonable to think that nutrients and water tied up in epiphyte biomass would be unavailable to trees. Indeed, for many species, epiphytes may slow the rate at which nutrients fall to and enter into the soil. However, trees like bigleaf and vine maples appear to be tapping into these nutrient and water-rich epiphyte mats.

A subcanopy of vine maple (Acer circinatum) draped in epiphytes.

Both bigleaf and vine maples (as well as a handful of other tree species) are capable of producing canopy roots. Wherever the epiphyte load is thick enough, bundles of cells just under the bark awaken and begin growing roots. This is a common phenomenon in the tropics, however, the canopy roots of these temperate trees differ in that they are indistinguishable in form and function from subterranean roots.

Canopy roots significantly increase the amount of foraging an individual tree can do for precious water and nutrients. Additionally, it has been found that canopy roots of the bigleaf maple even go as far as to partner with mycorrhizal fungi, thus unlocking even more potential for nutrient and water gain. In the absence of soil nutrient and water pools, a small handful of trees in the Pacific Northwest have unlocked a massive pool of nutrients located above us in the canopy. Amazingly, it has been estimated that mature bigleaf and vine maples with well developed epiphyte communities may actually gain a substantial fraction of their water and nutrient needs via their canopy roots.

Photo Credits: [2]

Further Reading: [1] [2] [3] [4] [5]

The Tecate Cypress: A Tree Left Hanging in the Balance

Photo by Anthonysthwd licensed under CC BY-SA 4.0

The tecate cypress is a relict. Its tiny geographic distribution encompasses a handful of sights in southern California and northwestern Mexico. It is a holdover from a time when this region was much cooler and wetter than it is today. It owes its survival and persistence to a combination of toxic soils, a proper microclimate, and fires that burn through every 30 to 40 years. However, things are changing for the Tecate cypress and they are changing fast. The fires that once ushered in new life for isolated populations of this tree are now so intense that they may spell disaster.

The taxonomy of the Tecate cypress has undergone a few revisions since it was first described. Early work on this species suggested it was simply a variety of Cupressus guadalupensis. Subsequent genetic testing revealed that these two trees were distinct enough to each warrant species status of their own. It was then given the name Cupressus forbesii, which will probably be familiar to most folks who know it well. Work done on the Tecate cypress back in 2012 has seen it moved out of the genus Cupressus and into the genus Hesperocyparis. As far as I am concerned, whether you call it Cupressus forbesii or Hesperocyparis forbesii matters not at this point.

The Tecate cypress is an edaphic endemic meaning it is found growing only on specific soil types in this little corner of the continent. It appears to prefer soils derived from ultramafic rock. The presence of high levels of heavy metals and low levels of important nutrients such and potassium and nitrogen make such soils extremely inhospitable to most plants. As such, the Tecate cypress experiences little competition from its botanical neighbors. It also means that populations of this tree are relatively small and isolated from one another.

Photo by Stan Shebs licensed under CC BY-SA 3.0

The Tecate cypress also relies on fire for reproduction. Its tiny cones are serotinous, meaning they only open and release seeds in response to a specific environmental trigger. In this case, it’s the heat of a wildfire. Fire frees up the landscape of competition for the tiny Tecate cypress seedlings. After a low intensity fire, literally thousands of Tecate cypress seedlings can germinate. Even if the parent trees burn to a crisp, the next generation is there, ready to take their place.

At least this is how it has happened historically. Much has changed in recent decades and the survival of these isolated Tecate cypress populations hangs in the balance. Fires that once gave life are now taking it. You see, decades of fire suppression have changed that way fire behaves in this system. With so much dry fuel laying around, fires burn at a higher intensity than they have in the past. What's more, fires sweep through much more frequently today than they have in the past due in large part to longer and longer droughts.

Photo by Stan Shebs licensed under CC BY-SA 3.0

Taken together, this can spell disaster for small, isolated Tecate cypress populations. Even if thousands of seedlings germinate and begin to grow, the likelihood of another fire sweeping through within a few years is much higher today. Small seedlings are not well suited to cope with such intense wildfires and an entire generation can be killed in a single blaze. This is troubling when you consider the age distributions of most Tecate cypress stands. When you walk into a stand of these trees, you will quickly realize that all are of roughly the same age. This is likely due to the fact that they all germinated at the same time following a previous fire event.

If all reproductive individuals come from the same germination event and wildfires are now killing adults and seedlings alike, then there is serious cause for concern. Additionally, when we lose populations of Tecate cypress, we are losing much more than just the trees. As with any plant, these trees fit into the local ecology no matter how sparse they are on the landscape. At least one species of butterfly, the rare Thorne's hairstreak (Callophrys gryneus thornei), lays its eggs only on the scale-like leaves of the Tecate cypress. Without this tree, their larvae have nothing to feed on.

Thorne's hairstreak (Callophrys gryneus thornei), lays its eggs only on the scale-like leaves of the Tecate cypress. Photo by USFWS Pacific Southwest Region licensed under CC BY 2.0

Although things in the wild seem uncertain for the Tecate cypress, there is reason for hope. Its lovely appearance and form coupled with its unique ecology has led to the Tecate cypress being something of a horticultural curiosity in the state of California. Seeds are easy enough to germinate provided you can get them out of the cones and the trees seem to do quite well in cultivation provided competition is kept to a minimum. In fact, specimen trees seem to adapt quite nicely to California's cool, humid coastal climate. Though the future of this wonderful endemic is without a doubt uncertain, hope lies in those who care enough to grow and cultivate this species. Better management practices regarding fire and invasive species, seed collection, and a bit more public awareness may be just what this species needs.

Photo Credits: [1] [2] [3] [4] [5]

Further Reading: [1] [2] [3] [4]

Why Are Some Plants Overcompensating?

Photo by CanyonlandsNPS licensed under public domain.

Gardeners are all too familiar with herbivory. Countless times I have been awaiting a bloom to burst only to have the buds nipped off the night before they opened. While this can be devastating for many plant species (not to mention my sanity), for certain plant species, an encounter with a hungry herbivore may actually lead to an increase in reproductive fitness.

Overcompensation theory is the idea that, under certain conditions, plants can respond to herbivore damage by producing more shoots, flowers, and seeds. It goes without saying that when this idea was originally proposed in the late 80's, it was met with its fair share of skepticism. Why would a plant capable of producing more shoots and flowers wait to be damaged to do so? The answer may lie in in the realm of biological trade-offs.

Overcompensation may evolve in lineages that tend to grow in habitats where there is a "predictable" amount of herbivory in any given growing season, perhaps a region where large herbivores migrate through annually. Plants in these habitats may conserve dormant growing tips and valuable resources to be used once herbivory has occurred. Perhaps this also serves as a cue to upregulate antiherbivory compounds in new tissues. The trade-off is that the plants incur a cost in the form of fewer flowers and thus reduced reproduction when herbivory is low or absent.

Scarlet gilia (Ipomopsis aggregata). Photo by Dcrjsr licensed under CC BY 3.0

It could also be that plants are exhibiting two different strategies - one to deal with competition and one to deal with herbivory. If herbivory is low, plants may become more competitive, thus favoring rapid vertical growth of one or a couple shoots. When herbivory is high, rapid vertical growth becomes disadventageous and overcompensatory branching and flowering can provide the higher fitness benefits.

These possibilities are not mutually exclusive. In fact, since the late 80's, experts now believe that overcompensation is not an "either/or" phenomenon but rather a spectrum of possibilities that are dictated by the conditions in which the plants are growing. Certainly overcompensation exists but which conditions favor it and which do not?

Research on scarlet gilia (Ipomopsis aggregata), a biennial native to western North America, suggests that overcompensation comes into play only when environmental conditions are most favorable. Soil nutrients seem to play a role in how well a plant can bounce back following herbivore damage. When resources are high, the results can be quite astounding. Early work on this species showed that under proper conditions, plants that were browsed by upwards of 95% produced 2.4 times as much seed as uneaten control plants. What's more, the resulting seedlings were twice as likely to survive than their uneaten counterparts.

Things change for scarlet gilia growing in poor conditions. Low resource availability appears to place limits on how much any given plant may respond to browsing. Also, herbivory can really hamper flowering time. Because scarlet gilia is pollen limited, anything that can cause a disruption in pollinator visits can have serious consequences for seed set. In at least one study, browsed plants flowered later and received fewer pollinator visits as a result.

More recent work has been able to add more nuance to the overcompensation story. For instance, experiments done on two subspecies of field gentian (Gentianella campestris), add further support to the idea that overcompensation is a matter of trade-offs. They showed that, whereas competition with neighboring plants alone could not explain the benefits of overcompensation, browsing certainly can.

Field gentian (Gentianella campestris). Photo by Joan Simon licensed under CC BY-SA 2.0

Plants growing in environments where herbivory was higher overcompensated by producing more branching, more flowers, and thus more seed, all despite soil nutrients. It appears that herbivory is the strongest predictor of overcompensation for this gentian. What's more, when these data were fed into population models, only the plants that responded to herbivory by overcompensation were predicted to show any sort of population growth in the long term.

Despite all of the interest overcompensation has recieved in the botanical literature, we are only just beginning to understand the biological mechanisms that make it possible. For starters, we know that when a dominant shoot or stem gets damaged or removed, it causes a reduction in the amount of the plant hormone auxin being produced. When auxin is removed, tiny auxiliary buds at the base of the plant are able to break dormancy and begin growing.

Removal of the dominant shoot or stem can also have major impact on the number of chromosomes present in regrowing tissues. Work on Arabidopsis thaliana revealed that when the apical meristem (main growing tip of a vertical stem) was removed, the plant underwent a process called "endoreduplication" in which the cells of the growing tissues actually duplicate their entire genome without undergoing mitosis.

Photo by Hectonichus licensed under CC BY-SA 3.0

Endoreduplication is a complex process with lots of biological significance but in plants it is often associated with stress responses. By duplicating the genomes of these new cells, the plants may be able to adjust more rapidly to their environment. This often manifests in changes to leaf size and shape and an uptick in plant defenses. Thus, plants may be able to fine tune the development of new tissues to overcompensate for browsing. Certainly far more work is needed to understand these mechanisms and their functions in more detail.

Overcompensation is not universal. Nonetheless, it is expected to occur in certain plants, especially those with short life cycles, and under certain environmental conditions, mainly when herbivore pressure and nutrient availability are relatively high. That being said, we still have plenty more to learn about this spectrum of strategies. When does it occur and when does it not? How common is it? What are the biological underpinnings of plants capable of overcompensation? Are some lineages more prone to overcompensation than others? Only more research can say for sure!

Photo Credits: [1] [2] [3] [4] [5]

Further Reading: [1] [2] [3] [4]

The Plight of the African Violets

Photo by RobertoMM licensed under CC BY-SA 3.0

For many of us, African violets (Saintpaulia spp.) are some of the first houseplants we learned how to grow. They are not true violets (Violaceae), of course, but rather members of the family Gesneriaceae. Nonetheless, their compact rosettes of fuzzy leaves coupled with regular sprays of colorful flowers has made them a multi-million dollar staple of the horticultural industry. Unfortunately their numbers in captivity overshadow a bleak future for this genus in the wild. Many African violets are teetering on the brink of extinction.

The genus Saintpaulia is endemic to a small portion of east Africa, with a majority of species being found growing at various elevations throughout the Eastern Arc Mountains of Kenya and Tanzania. Most of the plants we grow at home are clones and hybrids of two species, S. ionantha and S. confusa. Collected in 1892, these two species were originally thought to be the same species, S. ionantha, until a prominent horticulturist noted that there are distinct differences in the seed capsules each produced. Since the 1890's, more species have been discovered.

Saintpaulia goetzeana

Exactly how many species comprise this genus is still up for some debate. Numbers range from as many as 20 to as few as 6. Much of the early work on describing various Saintpaulia species involved detailed descriptions of the density and direction of hairs on the leaves. More recent genetic work considers some of these early delineations to be tenuous at best, however, even these modern techniques have resolved surprisingly little when it comes to a species concept within this group.

Saintpaulia sp. in situ. Photo by TanzaniaPlantCollaboration licensed under CC BY-NC-SA 2.0

Though it can be risky to try and make generalizations about an entire genus, there are some commonalities when it comes to the habitats these plants prefer. Saintpaulia grow at a variety of elevations but most can be found growing on rocky outcrops. Most of them prefer growing in the shaded forest understory, hence they do so well in our (often) poorly lit homes. Their affinity for growing on rocks means that many species are most at home growing on rocks and cliffs near streams and waterfalls. The distribution of most Saintpaulia species is quite limited, with most only known from a small region of forest or even a single mountain. Its their limited geographic distribution that is cause for concern.

Saintpaulia ionantha subsp. grotei in situ.

Regardless of how many species there are, one fact is certain - many Saintpaulia risk extinction if nothing is done to save them. Again, populations of Saintpaulia species are often extremely isolated. Though more recent surveys have revealed that a handful of lowland species are more widespread than previously thought, mid to highland species are nonetheless quite restricted in their distribution. Habitat loss is the #1 threat facing Saintpaulia. Logging, both legal and illegal, and farming are causing the diverse tropical forests of eastern Africa to shrink more and more each year. As these forests disappear, so do Saintpaulia and all of the other organisms that call them home.

There is hope to be had though. The governments of Kenya and Tanzania have recognized that too much is being lost as their forests disappear. Stronger regulations on logging and farming have been put into place, however, enforcement continues to be an issue. Luckily for some Saintpaulia species, the type localities from which they were described are now located within protected areas. Protection coupled with inaccessibility may be exactly what some of these species need to survive. Also, thanks to the ease in which Saintpaulia are grown, ex situ conservation is proving to be a viable and valuable option for conserving at least some of the genetic legacy of this genus.

Saintpaulia intermedia [source]

It is so ironic to me that these plants can be so common in our homes and offices and yet so rare in the wild. Despite their popularity, few recognize the plight of this genus. My hope is that, in reading this, many of you will think about what you can do to protect the legacy of plants like these and so many others. Our planet and the species that call it home are doomed without habitat in which to live and reproduce. This is why land conservation is an absolute must. Consider donating to a land conservation organization today. Here are two worth your consideration:

The Nature Conservancy

The Rainforest Trust

Photo Credits: [1] [2] [3] [4] [5]

Further Reading: [1] [2] [3] [4] [5]

Is Love Vine Parasitizing Wasps?

Photo by David Eickhoff licensed under CC BY 2.0

No, that's not dodder (Cuscuta sp.), its love vine (Cassytha filiformis), a member of the same family as the avacados in your kitchen (Lauraceae). It is a pantropical parasite that makes its living stealing water and nutrients from other plants. To do so, it punctures their vascular tissues with specialized structures called "haustoria." Amazingly, a recent observation made in Florida suggests that this botanical parasite may also be taking advantage of other parasites, specifically gall wasps.

Gall wasps are also plant parasites. They lay their eggs in developing plant tissues and the larvae release compounds that coax the plant to form nutrient-rich galls packed full of starchy goodness. Essentially you can think of galls as edible nursery chambers for the wasp larvae. While looking for galls on sand live oak (Quercus geminata) growing in southern Florida, Dr. Scott Egan and his colleagues noticed something odd. A small vine seemed to be attaching itself to the galls.

Love vine draping a host plant. Photo by Forest & Kim Starr licensed under CC BY 3.0

The vine in question was none other than love vine and they were attached to galls growing on the underside of the oak leaves. What is strange is that, of all of the places that love vine likes to attach itself to its host (new stems, buds, petioles, and on the top and edge of leaves), the only time this vine showed any "interest" in the underside of oak leaves was when galls were present. Obviously this required further investigation.

The team discovered that at least two different species of gall wasps were being parasitized by love vine - one that produces small, spherical galls on the underside of oak leaves and one that forms large, multi-chambered galls on oak stems. Upon measuring the infected and uninfected galls, the team discovered that there were significant differences that could have real ecological significance.

(A) Cassytha filiformis vine attaching haustoria to a leaf gall induced by the wasp Belonocnema treatae on the underside of their host plant, Quercus geminata. (B) Labeled graphic of insect gall, parasitic vine, and vine haustoria. (C) Box plots of leaf gall diameter for unparasitized galls (control) and galls that have been parasitized by C. filiformis. (D) Proportion of B. treatae leaf galls that contained a dead ‘mummified’ adult for unparasitized galls (control) and galls that have been parasitized by the vine C. filiformis. [SOURCE]

For the spherical gall wasp, infected galls tended to be much larger, however, the team feels that this may actually be due to the fact that the vine "prefers" larger galls. Astonishingly, larvae living in the infected galls were 45% less likely to survive. For the multi-chambered gall wasp, infection by love vine was associated with a 13.5% decrease in overall gall size. They suggest this is evidence that love vine is having net negative impacts on these parasitic wasps.

Subsequent investigation revealed that these wasps were not alone. In total, the team found love vine attacking the galls of at least two other wasps and one species of gall-making fly (though no data were reported for these cases). To be sure that love vine was in fact parasitizing these galls, they needed to have a closer look at what the vine was actually doing.

Figure S2. (A) Cassytha filiformis vine attaching haustoria to a leaf gall induced by the wasp Callirhytis quercusbatatoides on the stem of their host plant, Quercus geminata. (B) Labeled graphic of insect gall, parasitic vine, and vine haustoria on C. quercusbatatoides. (C) Exemplar of parasitic vine wrapping tightly around the stem directly proximate to a gall induced by the wasp Disholcaspis quercusvirens on Q. geminata. (D) Field site where love vine, C. filiformis, is attacking the sand live oak, Q. geminata, and many of the gall forming wasps on the same host plant. [SOURCE]
 

Dissection of the galls revealed that the haustoria were plugged into the gall itself, not the wasp larvae. However, because the larvae simply cannot develop without the nutrients and protection provided by the gall, Eagan and his colleagues conclude that these do indeed represent a case of a parasite being parasitized by another parasite.

At this point, the next question that must be asked is how common is this in love vine or, for that matter, across all other parasitic plants that utilize haustoria. Considering that parasites of parasites are nothing new in the biosphere, it is a safe bet that this will not be the last time this phenomenon is discovered.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1]

The Carnivorous Dewy Pine

Photo by David Eickhoff licensed under CC BY-NC-SA 2.0

The dewy pine is definitely not a pine, however, it is quite dewy. Known scientifically as Drosophyllum lusitanicum, this carnivore is odd in more ways than one. It is also growing more and more rare each year.

One of the strangest aspects of dewy pine ecology is its habitat preferences. Whereas most carnivorous plants enjoy growing in saturated soils or even floating in water, the dewy pine's preferred habitats dry up completely for a considerably portion of the year. Its entire distribution consists of scattered populations throughout the western Iberian Peninsula and northwest Morocco.

Photo by Javier martin licensed under CC BY-SA 3.0

Its ability to thrive in such xeric conditions is a bit of a conundrum. Plants stay green throughout the year and produce copious amounts of sticky mucilage as a means of catching prey. During the summer months, both air and soil temperatures can skyrocket to well over 100°F (37 °C). Though they possess a rather robust rooting system, dewy pines don't appear to produce much in the way of fine roots. Because of this, any ground water presence deeper in the soil is out of their reach. How then do these plants manage to function throughout the driest parts of the year?

During the hottest months, the only regular supply of water comes in the form of dew. Throughout the night and into early morning, temperatures cool enough for water to condense out of air. Dew covers anything with enough surface area to promote condensation. Thanks to all of those sticky glands on its leaves, the dewy pine possesses plenty of surface area for dew to collect. It is believed that, coupled with the rather porous cuticle of the surface of its leaves, the dewy pine is able to obtain water and reduce evapotranspiration enough to keep itself going throughout the hottest months. 

Dewy pine leaves unfurl like fern fiddle heads as they grow. Photo by Mark Freeth licensed under CC BY 2.0

As you have probably guessed at this point, those dewy leaves do more than photosynthesize and collect water. They also capture prey. Carnivory in this species evolved in response to the extremely poor conditions of their native soils. Nutrients and minerals are extremely low, thus selecting for species that can acquire these necessities via other means. Each dewy pine leaf is covered in two types of glands: stalked glands that produce sticky mucilage, and sessile glands that secrete digestive enzymes and absorb nutrients.

Their ability to capture insects far larger than one would expect is quite remarkable. The more an insect struggles, the more it becomes ensnared. The strength of the dewy pines mucilage likely stems from the fact that the leaves do not move like those of sundews (Drosera spp.). Once an insect is stuck, there is not much hope for its survival. Living in an environment as extreme as this, the dewy pine takes no chances.

Photo by Strombus72 licensed under CC BY-SA 4.0

The taxonomic affinity of the dewy pine has been a source of confusion as well. Because of its obvious similarity to the sundews, the dewy pine has long been considered a member of the family Droseraceae. However, although recent genetic work does suggest a distant relationship with Droseraceae and Nepenthaceae, experts now believe that the dewy pine is unique enough to warrant its own family. Thus, it is now the sole species of the family Drosophyllaceae.

Sadly, the dewy pine is losing ground fast. From industrialization and farming to fire suppression, dewy pines are running out of habitat. It is odd to think of a plant capable of living in such extreme conditions as being overly sensitive but that is the conundrum faced by more plants than just the dewy pine. Without regular levels of intermediate disturbance that clear the landscape of vegetation, plants like the dewy pine quickly get outcompeted by more aggressive plant species. Its the fact that dewy pine can live in such hostile environments that, historically, has kept its populations alive and well.

Photo by Javier martin licensed under Public Domain

What's more, it appears that dewy pines have trouble getting their seeds into new habitats. Low seed dispersal ability means populations can be cut off from suitable habitats that are only modest distances away. Without a helping hand, small, localized populations can disappear alarmingly fast. The good news is, conservationists are working hard on identifying what must be done to ensure the dewy pine is around for future generations to enjoy.

Changes in land use practices, prescribed fires, wild land conservation, and incentives for cattle farmers to adopt more traditional rather than industrial grazing practices may turn the table on dewy pine extinction. Additionally, dewy pines have become a sort of horticultural oddity over the last decade or so. As dedicated growers perfect germination and growing techniques, ex situ conservation can help maintain stocks of genetic material around the globe.

Photo Credits: [1] [2] [3] [4] [5]

Further Reading: [1] [2] [3] [4]

Fluorescent Bananas

Photo by endolith licensed under CC BY-SA 2.0

Bananas are one of the most popular fruits in the world. Love them or hate them, most of us know what they look like. Despite their global presence, few stop to think about where these fruits come from. That is a shame because bananas are fascinating plants for many reasons but now we can add blue fluorescence to that list.

Before we dive into the intriguing phenomenon of fluorescence in bananas, I think it is worth talking about the plants that produce them in a little more detail. Bananas belong to the genus Musa, which is located in its own family - Musaceae. Take a step back and look at a banana plant and it won't take long to realize they are distant relatives of the gingers. There are at least 68 recognized species of banana in the world and many more cultivated varieties. Despite their pan-tropical distribution, the genus Musa is native only to parts of the Indo-Malesian, Asian, and Australian tropics.

Photo by Forest & Kim Starr licensed under CC BY 3.0

Banana plants vary in height from species to species. At the smaller end of the spectrum you have species like the diminutive Musa velutina, which maxes out at about 2 meters (6 ft.) in height. On the taller side of things, there are species such as the monstrous Musa ingens, which can reach heights of 20 meters (66ft.)! Despite their arborescent appearance, bananas are not trees at all. They do not produce any wood. Instead, what looks like a tree trunk is actually the fused petioles of their leaves. Bananas are essentially giant herbs with the aforementioned M. ingens holding the world record for largest herb in the world.

When it comes time to flower, a long spike emerges from the main growing tip. This spike gradually elongates, revealing long, beautiful, tubular flowers arranged in whorls. For many banana species, bats are the main pollinators, however, a variety of insects will visit as well. In the wild, fruits appear following pollination, a trait that has been bred out of their cultivated relatives, which produce fruits without needing pollination. The fruits of a banana are actually a type a berry that dehisce like a capsule upon ripening, revealing delicious pulp chock full of hard seeds. Not all bananas turn yellow upon ripening. In fact, some are pink!

CC0 Public Domain

For many fruits, the act of ripening often coincides with a change in color. This is a way for the plant to signal to seed dispersers that the fruits, and the seeds inside, are ready. As many of us know, many bananas start off green and gradually ripen to a bright yellow. This process involves a gradual breakdown of the chlorophyll within the banana skin. As the chlorophyll within the skin of a banana breaks down, it leaves behind a handful of byproducts. It turns out, some of these byproducts fluoresce blue under UV light. 

Amazingly, the fluorescent properties of bananas was only recently discovered. Researchers studying chlorophyll breakdown in the skins of various fruits identified some intriguing compounds in the skins of ripe Cavendish bananas. When viewed under UV light, these compounds gave off a luminescent blue hue. Further investigation revealed that as bananas ripen, their fluorescent properties grow more and more intense.

There could be a couple reasons why this happens. First, it could simply be happenstance. Perhaps these fluorescent compounds are simply a curious byproduct of chlorophyll breakdown and serve no function for the plant whatsoever. However, bananas seem to be a special case. The way in which chlorophyll in the skin of a banana breaks down is quite different than the process of chlorophyll breakdown in other plants. What's more, the abundance of these compounds in the banana skin seems to suggest that the fluorescence does indeed have a function - seed dispersal.

Researchers now believe that the fluorescent properties of some ripe bananas serves as an additional signal to potential seed dispersers that the time is right for harvest. Many animals including birds and some mammals can see well into the UV spectrum and it is likely that the blue fluorescence of these bananas is a means of attracting such animals. Additionally, researchers also found that banana leaves fluoresce in a similar way, perhaps to sweeten the attractive display of the ripening fruits.

To date, little follow up has been done on fluorescence in bananas. It is likely that far more banana species exhibit this trait. Certainly more work is needed before we can say for sure what role, if any, these compounds play in the lives of wild bananas. Until then, this could be a fun trait to investigate in the comfort of your own home. Grab a black light and see if your bananas glow blue!

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2]

Light Pollution and Plants

I love walking around my town at night. Things really seem to slow down when the sun sets. Growing up in the country, my evening walks were lit only by the moon. Now that I live in civilization, however, street lights punctuate the darkness on every block. Walking around I can't help but wonder what all of this artificial light is doing to our photosynthetic neighbors. 

The vast majority of plants need light to make food. It doesn't matter if this light comes from the sun or a high powered electric light, as long as it is strong enough for photosynthesis. Even weaker wavelengths of light serve a purpose for our botanical friends. Plants can sense the relative length of uninterrupted darkness in their environment and they use that information for myriad internal processes. Its this dependence on light that makes many plant species vulnerable to our addiction to artificial lighting.

Just because a light isn't strong enough for photosynthesis doesn't mean it isn't affecting nearby plants. This is especially true for plants that use day length for timing events like bud break, flowering, and dormancy. The type of lighting favored by most municipalities emit wavelengths that peak especially high in the red to far-red ratio of the electromagnetic spectrum, which makes them particularly adept at disrupting plant photoperiods.

One of the most obvious effects of artificial lighting on plants can readily be seen in street trees growing in temperate regions. Though light sensitivity varies from species to species, trees growing near street lights tend to hold onto their leaves much longer in the fall than trees farther away. Because artificial lighting is enough to trick the red to far-red receptors in plants, it can "convince" trees that the days are longer than they actually are. Additional photosynthesis may not seem that bad but holding onto leaves longer makes trees more susceptible to ice damage. 

[source]

The effects of artificial lighting continues into spring as well. Trees growing near lights tend to break buds and flower earlier in the spring. This too makes them susceptible to frost damage. Early flowering plants run the risk of losing their entire reproductive effort by blooming before the threat of frost is gone. This can really mess up their relationship with pollinators. 

The effects of artificial lighting can even influence the way in which plants grow. Research has found that plants growing near street lights had larger leaves with more stomatal pores and these pores remained open for considerably longer than plants growing under unlit night conditions. This made them more susceptible to pollution and drought, two stressors that are all too common in urban environments. This issues is made much worse if the artificial lighting never turns off throughout the night. 

Artificial lighting affects more than just plant physiology too. Scaling up, the effects of night lights can have whole ecosystem consequences. For instance, researchers found that artificial lighting was enough to change the entire composition of grassland communities. Some plants responded well to artificial lights, producing more biomass and vegetative offshoots to the point that they pushed out other species. This was compounded by the change in reproductive output, with certain species showing higher seed production than others.

Photo by Lamiot licensed under CC BY-SA 4.0

Changes in plant physiology, phenology, and composition also affect myriad other organisms in the environment. Changes in the timing of flowering or bud break can disrupt things like insects and birds that rely on these events for food and shelter. Research even suggests that forest regeneration is being altered by artificial lighting. Seed dispersers such as bats often will not fly into well-lit areas at night, therefore reducing the amount of seeds falling in those areas. Such research is still in its infancy meaning we have a lot more to learn about how artificial lighting is disrupting natural events.

Light pollution is so much more than an aesthetic issue. Artificial lighting is clearly having pronounced effects on plant life. Disrupt plants and you disrupt life as we know it. Certainly more work is needed to tease out all the ways in which lights influence plants, however, it is clear that we must work hard on reducing light pollution around the globe.

Photo Credits: [1] [2] [3]

Further Reading: [1] [2] [3]

Fossils Shine Light On the History of Gall-Making Wasps

M J Richardson / Common spangle galls / CC BY-SA 2.0

We can learn a lot about life on Earth from the fossil record. I am always amazed by the degree of scrutiny involved in collecting data from these preserved remains. Take, for instance, the case of gall-making wasp fossils found in western North America. A small collection of fossilized oak leaves is giving researchers insights into the evolutionary history of oaks and the gall-making wasps they host.

Oaks interact with a bewildering array of insects. Many of these are gall-making wasps in the family Cynipidae. Dozens of different wasp species can be found on a single oak tree. Female wasps lay their eggs inside developing oak tissues and the larvae release hormones and other chemicals that cause galls to form. Galls are essentially edible nursery chambers. Other than their bizarre shapes and colors, the compounds released by the wasp larvae reduce the chemical defenses of the oak and increase the relative nutrition of the tissues themselves. Often, these relationships are precise, with specific wasp species preferring specific oak species. But when did these relationships arise? Why are oaks so popular? What can fossil evidence tell us about this incredible relationship?

Photo by Beentree licensed under CC BY-SA 4.0

Though scant, the little fossil evidence of oak galls can tell us a lot. For starters, we know that gall-making wasps whose larvae produce structures similar to that of the Cynipids have been around since at least the late Cretaceous, some 100 million years ago. However, it is hard to say for sure exactly who made these galls and exactly what taxonomic affinity the host plant belongs to. More conclusive Cynipid gall fossils appear again in the Eocene and continue to pop up in the fossil record throughout the Oligocene and well into the Miocene (33 - 23 million years ago).

Miocene aged fossils are where things get a little bit more conclusive. Fossil beds located in the western United States have turned up fossilized oak leaves complete with Cynipid galls. The similarity of these galls to those of some present day species is incredible. It demonstrates that these relationships arose early on and have continued to diversify ever since. What's more, thanks to the degree of preservation in these fossil beds, researchers are able to make some greater conclusions about why gall-making wasps and oaks seem to be so intertwined.

Holotype of Antronoides cyanomontanus galls on fossilized leaves of Quercus simulata. 1) Impression of the abaxial surface of the leaf, showing the galls extending into the matrix. 2) Galls showing close association with secondary veins. 3) Gall showing the impression of rim-like base partially straddling the secondary vein. 4) Close-up of gall attached at margin extending down into the matrix. 5) Gall uncovered revealing spindle-shaped morphology.

1) Xanthoteras clavuloides galls on fossilized Quercus lobata, showing gall attached to secondary vein. Specimen in California Academy of Sciences Entomology collection, San Francisco. 2) Two galls of attached to a secondary vein showing overlap of their bases. Specimen in California Academy of Sciences Entomology Collection, San Francisco. 3) Three galls collected from leaf of California Quercus lobata showing clavate shape and expanded, ring-like base. 4) Gall showing the annulate or ribbed aspect of the base, which is similar to bases of Antronoides cyanomontanus and A. polygonalis. 5) Galls showing clavate shape, pilose and nonpilose surfaces, and bases.

Gall-making wasps seem to diversify at a much faster rate in xeric climates. The fossil records during this time show that mesic tree speciess were gradually being replaced by more xeric species like oaks. Wasps seem to prefer these drier environments and the thought is that such preferences have to do with disease and parasite loads.

Again, galls a large collections of nutrient-rich tissues that are low in defense compounds. Coupled with the juicy grub at their center, it stands to reason that galls make excellent sites of infection for fungi and other parasites. By living in drier habitats, it is believed that gall-making wasps are able to escape these environmental pressures that would otherwise plague them in wetter habitats. The fossil evidence appears to support this hypothesis and today we see similar patterns. White oaks are especially drought tolerant and its this group of oaks that host the highest diversity of gall-making wasps.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3]

Meet the Blazing Stars

Midsummer in North America is, among other things, Liatris season. These gorgeous plants are often referred to as blazing stars or gayfeathers, which hints at the impact their flowers have on our psyche. Whether in the garden or in the wild, Liatris are a group of plants worth getting to know a bit better.

Liatris is by and large a North American genus with only a single species occurring in the Bahamas. Though we often think of Liatris as prairie plants, the center of diversity for this group is in the southeastern United States. Taxonomically speaking, Liatris are a bit of a conundrum. Something like 40 different species have been described and, where ranges overlap, many putative hybrids have been named.

Rocky Mountain blazing star (Liatris ligulistylis). Photo by Dan Mullen licensed under CC BY-NC-ND 2.0

Authorities on this group cite ample confusion when it comes to drawing lines between species. Much of this confusion comes from the fact that numerous variants and intergradations exist between the various species. As mentioned, hybridization is not uncommon in this genus, which complicates matters quite a bit.

Prairie blazing star (Liatris pycnostachya). Photo by Kcauley licensed under CC BY-SA 4.0

Liatris as a whole appears to have undergone quite an adaptive radiation in North America, with species adapting to specific soils and habitat types. Take, for instance, the case of cylindrical blazing star (L. cylindracea), marsh blazing star (L. spicata), and rough blazing star (L. aspera). The ranges of these species overlap to quite a degree, however, each prefers to grow in soils of specific texture and moisture. Marsh blazing star, as you may have guessed, prefers wetter soils whereas rough blazing star enjoys drier habitats. Cylindrical blazing star seems to enjoy intermediate soil conditions, especially where soil pH is a bit higher. As such, these three species often occur in completely different habitats. However, in places like the southern shores of Lake Michigan, they find themselves growing in close quarters and as a result, a fair amount of hybridization has occurred.

Another example of confusion comes from a species commonly known as the savanna blazing star (Liatris scariosa nieuwlandii). Many different ecotypes of this plant exist and some experts don't quite know how to deal with them all. Sometimes savanna blazing star is treated as a variant of another species called the northern blazing star (Liatris scariosa var. nieuwlandii) and sometimes it is treated as its own distinct species (Liatris nieuwlandii). Until proper genetic work can be done, it is impossible to say which, if any, are correct. 

Glandular blazing star (Liatris glandulosa). Photo by Billy Bob Bain licensed under CC BY 2.0

Taxonomic confusion aside, the various Liatris species and variants are important components of the ecology wherever they occur. Numerous insects feed upon and raise their young on the foliage and few could argue against their flowers as pollinator magnets. All Liatris produce pink to purple flowers in splendid Asteraceae fashion. Every once in a while, an aberrant form is produced that sports white flowers. Though horticulturists have capitalized on this for the garden, at least one authority claims that these white forms are much weaker than their pink flowering parents. At least one species, the pinkscale blazing star (L. elegans), produces large, filamentous white bracts that very much resemble flowers.

Check out the bracts on the pinkscale blazing star (L. elegans)!

Liatris are just as interesting below as they are above. The roots, foliage, and flowers all emerge from a swollen underground stem called a corm. The formation of these corms is one reason why some Liatris species have become so popular in our gardens. It makes them extremely hardy during the dormant season. In the spring, the corm starts forming roots. At the same time, tiny preformed buds at the top of the corm begin to grow this years crop of leaves and flowers. By the end of the growing season, the corm has reached its maximum size for that year and the plant draws down the rest of its reserves to wait out the winter.

Cylindrical blazing star (Liatris cylindracea). Photo by Joshua Mayer licensed under CC BY-SA 2.0

During this time, some species form a layer of tissue along the edge of the corm that is much darker in coloration than what was laid down earlier in the season. This has led some to suggest that aging individual Liatris is possible. Experts believe that specimens can readily reach 30 to 40 years of age or more, however, the degree to which these dark bands indicate annual growth is up for a lot of debate. Others have found no correlation with plant age. Regardless, it is safe to say that many Liatris species can live for decades if left undisturbed.

Scrub blazing star (Liatris ohlingerae). Photo by FWC Fish and Wildlife Research Institute licensed under CC BY-NC-ND 2.0

All in all, Liatris is a very special, albeit slightly confusing, group of plants. It offers a little something for everyone. What's more, their beauty is only part of the story. These are ecologically important plants that support many great insect species. As summer wears on, make sure to get out there and enjoy the Liatris in your neck of the woods. You will be happy you did!

Photo Credits: [1] [2] [3] [4] [5] [6] [7] [8]

Further Reading: [1] [2] [3]

Giant Hogweed And Other Toxic Plants

Photo by Jean-Pol GRANDMONT licensed under CC BY 3.0

Everybody run, giant hogweed is coming! I am sure by now, many of you reading this will have picked up a story or two about a nasty invasive plant that will render you blind and nursing third degree burns. Indeed, giant hogweed (Heracleum mantegazzianum) is a plant worth learning how to identify. However, the tone of these articles is often one of hysterics, leaving the reader feeling like this plant is more like a Triffid, actively uprooting itself to hunt down unwary humans. Is giant hogweed worth all of this anxiety?

Let's start with the plant itself. Giant hogweed is a member of the carrot family (Apiaceae). Its native range encompasses much of the Caucasus region and into parts of central Asia. It was (and probably still is in some areas) considered a wonderfully large and unique addition to a temperate garden. And large it is. Individual plants regularly reach heights of 6 feet (2 m) or more and some records indicate that individuals over 10 feet (3 m) in height are not unheard of.

Photo by Jean-Pol GRANDMONT licensed under CC BY 3.0

Because it was once a popular garden plant, this species has been introduced far outside of its native range. For many decades, giant hogweed probably lurked in the background unnoticed, its seeds finding favorable spots for germination among other weedy plants along roadsides, fallow fields, and abandoned lots. In the last few years it has grown harder to ignore. More and more plants are showing up where they shouldn't. Indeed, it seems that giant hogweed is yet another invasive species we need to get on top of. But what about all of that panic? Certainly its invasive status alone isn't what all the hype is about.

Well, like all members of the carrot family, giant hogweed produces an impressive array of chemical compounds. Many of these compounds serve to protect the plants from hungry herbivores and a plethora of microbial infections. Some of the compounds in the giant hogweed arsenal are a group known as the furocoumarins. These compounds defend the plant in a rather alarming way. These furocoumarins are phototoxic, which means when the sap gets on the body of an animal and is exposed to sunlight, they cause severe chemical burns.

Stories of people being hospitalized due to an unfortunate run in with this plant make headlines wherever it pops up. That being said, simply touching the plant isn't going to hurt you. The chemicals are sloshing around in the sap of giant hogweed and the plant needs to be injured in some way before they will leak out onto whatever is hurting it. For humans, this usually occurs while mowing or weed whacking, or if a child mistakenly uses the hollow stem as a pea shooter.

With stories like this floating around, it is no wonder then why people get so upset when this plant shows up. However, I can't help but feel that this is being fed on a bit by media fear-mongering. It is worth putting giant hogweed into some practical context. It may actually alarm you to know just how many plants on the landscape have the ability to cause you harm if handled the wrong way.

Wild parsnip (Pastinaca sativa). Photo by USFWS Midwest Region

Even hogweeds less robust relatives are capable of causing phototoxic reactions. I once weed whacked a large patch of Queen Anne's lace (Daucus carota) and wild parsnip (Pastinaca sativa) and ended up covered in nasty blisters the next day. I recovered but I sure did learn to give those two species more respect whenever I encountered them. Plants like poison ivy, oak, and sumac certainly cause their fair share of misery but even these do not get the sort of media attention that giant hogweed does.

Even more interesting are some of the species we actively plant in our gardens. For instance, castor bean (Ricinus communis) is quite popular among gardeners and it is responsible for producing ricin, a protein with enough killing power to bring down an adult human many times over. Take a bite out of the castor bean in your garden and it will be the last thing you ever eat. Even more potent than ricin is aconitine, an alkaloid produced by beloved garden plants like the monkshoods (Aconitum spp.) and the larkspurs (Delphinium spp.). This powerful alkaloid causes your nervous system to endlessly fire, leading to convulsions and death.

Castor bean (Ricinus communis). Photo by Jason Hollinger licensed under CC BY 2.0

Similarly, a few different species of Datura are commonly grown around the world. Datura posioning is nothing to mess with and symptoms include "a complete inability to differentiate reality from fantasy; hyperthermia; tachycardia; bizarre, and possibly violent behavior; and severe mydriasis (dilated pupils) with resultant painful photophobia that can last several days." Even plants we grow for food can hurt us in bad ways. Most members of the tomato family produce a multitude of toxic alkaloids like solanine. That is why only ripe tomatoes and eggplants should ever be consumed.

Jimsonweed (Datura stramonium). Photo by Al_HikesAZ licensed under CC BY-NC 2.0

In reality, I could devote an entire blog and podcast series to the chemical warfare plants have taken up during their long and complicated evolutionary history. Long story short, plants are sessile organisms that must defend themselves in order to survive and toxic chemicals are really great means to do just that. The reality is that we welcome many toxic and potentially harmful plants (both knowingly and unknowingly) into our lives and it seems slightly odd that species like giant hogweed warrant such fervor from media outlets. That being said, it is important to treat these plants with the respect they deserve. Don't bother them and they won't bother you.

So, is giant hogweed coming to attack you and your family? No. Is giant hogweed a plant worth learning to identify? Yes. Is giant hogweed dangerous to humans? Yes, but only under certain conditions.

Plants like giant hogweed are the perfect reminder as to why we must give plants more respect in our society. Teaching friends and family which plants can feed them and which plants can hurt them is something everyone should invest some time in doing. If you find giant hogweed in your area and you do not live in the Caucasus or central Asia, don't be a hero. Call a professional to come and deal with it. Otherwise, stay calm and keep on botanizing. Giant hogweed is not out to get you.

Photo Credits: [1] [2] [3] [4] [5] [6] [7]

Further Reading: [1] [2] [3]

Life With Endophytic Fungi

Endophytic fungi living in the cells of a grass leaf. Photo by Nick Hill (Public Domain)

Talk about plants long enough and fungi eventually make their way into the conversation. These two walks of life are inextricably linked and probably have been since the earliest days. At this point we are well aware of beneficial fungal partners like mycorrhizae or pathogens like the cedar apple rust. Another type of relationship we are only starting to fully appreciate is that of plants and endophytic fungi living in their above ground tissues. 

Endophytic fungi have been discovered in many different types of plants, however, it is best studied in grasses. The closer we look at these symbiotic relationships, the more complex the picture becomes. There are many ways in which plants can benefit from the presence of these fungi in their tissues and it appears that some plants even stock their seeds with fungi, which appears to give their offspring a better chance at establishment. 

To start, the benefits to the fungi are rather straight forward. They get a relatively safe place to live within the tissues of a plant. They also gain access to all of the carbohydrates the plants produce via photosynthesis. This is not unlike what we see with mycorrhizae. But what about the plants? What could they gain from letting fungi live in and around their cells?

One amazing benefit endophytic fungi offer plants is protection. Fungi are famous for the chemical cocktails they produce and many of these can harm animals. Such benefits vary from plant to plant and fungi to fungi, however, the overall effect is largely the same. Herbivores feeding on plants like grasses that have been infected with endophytic fungi are deterred from doing so either because the fungi make the plant distasteful or downright toxic. It isn't just big herbivores that are deterred either. Evidence has shown that insects are also affected.

There is even some evidence to suggest that these anti-herbivore compounds might have influences farther up the food chain. It usually takes a lot of toxins to bring down a large herbivore, however, some of these toxins have the potential to build up in the tissues of some herbivores and therefore may influence their appeal to predators. Some have hypothesized that the endophytic fungal toxins may make herbivores more susceptible to predators. Perhaps the toxins make the herbivores less cautious or slow them down, making them more likely targets. Certainly more work is needed before anyone can say for sure.

Italian ryegrass (Lolium multiflorum) is one of the most studied grasses that host endophytic fungi. Photo by Matt Lavin licensed under CC BY-SA 2.0

Another amazing example deals with parasitoids like wasps that lay their eggs in other insects. Researchers found that female parasitoid wasps can discriminate between aphids that have been feeding on plants with endophytic fungi and those without endophytic fungi. Wasp larvae developed more slowly and had a shorter lifespan when raised in aphids that have fed on endophytic fungi plants. As such, the distribution of plants with endophytic symbionts may have serious ramifications for parasitoid abundance in any given habitat.

Another benefit these endophytic fungi offer plants is increased photosynthesis. Amazingly, some grasses appear to photosynthesize better with endophytic fungi living in their tissues than plants without fungi. There are many mechanisms by which this may work but to simplify the matter, it appears that by producing defense compounds, endophytic fungi allow the plant to redistribute their metabolic processes towards photosynthesis and growth. In return, the plants produce more carbohydrates that then feed the fungi living in their tissues. 

One of the most remarkable aspects about the relationship between endophytic fungi and plants is that the plants can pass these fungi on to their offspring. Fungi are able to infect the tissues of the host plants' seeds and therefore can be carried with the seeds wherever they go. As the seedlings grow, so do the fungi. Some evidence suggests this gives infected seedlings a leg up on the competition. Other studies have not found such pronounced effects.

Still other studies have shown that it may not be fungi in the seeds that make a big difference but rather the fungi present in the decaying tissues of plants growing around them. Endophytic fungi have been shown to produce allelopathic compounds that poison neighboring plants. Areas receiving lots of plant litter containing endophytic fungi produced fewer plants but these plants grew larger than areas without endophytic fungi litter. Perhaps this reduces competition in favor of plant species than can host said endophytes. Again, this has potentially huge ramifications for the diversity and abundance of plant species living in a given area.

We are only beginning to understand the role of endophytic fungi in the lives of plants and the communities they make up. To date, it would appear that endophytic fungi are potentially having huge impacts on ecosystems around the globe. It goes without saying that more research is needed.

Photo Credits: [1] [2]

Further Reading: [1] [2] [3] [4] [5] [6]

Toxic Nectar

I was introduced to the concept of toxic nectar thanks to a species of shrub quite familiar to anyone who has spent time in the Appalachian Mountains. Locals will tell you to never place honeybee hives near a patch of rosebay (Rhododendron maximum) for fear of so-called "mad honey." Needless to say, the concept intrigued me.

A quick internet search revealed that this is not a new phenomenon either. Humans have known about toxic nectar for thousands of years. In fact, honey made from feeding bees on species like Rhododendron luteum and R. ponticum has been used more than once during times of war. Hives containing toxic honey would be placed along known routs of Roman soldiers and, after consuming the seemingly innocuous treat, the soldiers would collapse into a stupor only to be slaughtered by armies lying in wait.

Rhododendron luteum. Photo by Chrumps licensed under CC BY 3.0

The presence of toxic nectar seems quite confusing. The primary function of nectar is to serve as a reward for pollinators after all. Why on Earth would a plant pump potentially harmful substances into its flowers?

It is worth mentioning at this point that the Rhododendrons aren't alone. A multitude of plant species produce toxic nectar. The chemicals that make them toxic, though poorly understood, vary almost as much as the plants that make them. Although there have been repeated investigations into this phenomenon, the exact reason(s) remain elusive to this day. Still, research has drummed up some interesting data and many great hypotheses aimed at explaining the patterns.

Catalpa nectar has been shown to deter some ants and butterflies but not large bees. Photo by Le.Loup.Gris licensed under CC BY-SA 3.0

The earliest investigations into toxic nectar gave birth to the pollinator fidelity hypothesis. Researchers realized that meany bees appear to be less sensitive to alkaloids in nectar than are some Lepidopterans. This led to speculation that perhaps some plants pump toxic compounds into their nectar to deter inefficient pollinators, leading to more specialization among pollinating insects that can handle the toxins.

Another hypothesis is the nectar robber hypothesis. This hypothesis is quite similar to the pollinator fidelity hypothesis except that it extends to all organisms that could potentially rob nectar from a flower without providing any pollination services. As such, it is a matter of plant defense.

The nectar of Cyrilla racemiflora is thought to be toxic to some bees. Photo by Koala:Bear licensed under CC BY-SA 2.0

Others feel that toxic nectar may be less about pollinators or nectar robbers and more about microbial activity. Sugary nectar can be a breeding ground for microbes and it is possible that plants pump toxic compounds into their nectar to keep it "fresh." If this is the case, the antimicrobial benefits could outweigh the cost to pollinators that may be harmed or even deterred by the toxic compounds.

Finally, it could be that toxic nectar may have no benefit to the plant whatsoever. Perhaps toxic nectar is simply the result of selection for defense compounds elsewhere in the plant and therefore is expressed in the nectar as a result of pleiotropy. If this is the case then toxic nectar might not be under as strong selection pressures as is overall defense against herbivores. If so, the plants may not be able to control which compounds eventually end up in their nectar. Provided defense against herbivores outweighs any costs imposed by toxic nectar then plants may not have the ability to evolve away from such traits.

Where Spathodea campanulata is invasive, its nectar causes increased mortality in native bee hives. Photo by mauro halpern licensed under CC BY 2.0

So, where does the science land us with these hypotheses? Do the data support any of these theories? This is where things get cloudy. Despite plenty of interest, evidence in support of the various hypotheses is scant. Some experiments have shown that indeed, when given a choice, some bees prefer non-toxic to toxic nectar. Also, toxic nectar appears to dissuade some ants from visiting flowers, however, just as many experiments have demonstrated no discernible effect on bees or ants. What's more, at least one investigation found that the amount of toxic compounds within the nectar of certain species varies significantly from population to population. What this means for pollination is anyone's' guess.

It is worth noting that most of the pollination-related hypotheses about toxic nectar have been tested using honeybees. Because they are generalist pollinators, there could be something to be said about toxic nectar deterring generalist pollinators in favor of specialist pollinators. Still, these experiments have largely been done in regions where honeybees are not native and therefore do not represent natural conditions.

Simply put, it is still too early to say whether toxic nectar is adaptive or not. It could very well be that it does not impose enough of a negative effect on plant fitness to evolve away from. More work is certainly needed. So, if you are someone looking for an excellent thesis project, here is a great opportunity. In the mean time, do yourself a favor and don't eat any mad honey.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3] [4] [5] [6]

Resisting the Wind

Have you ever wondered how some plants can withstand heavy winds? At lease one group, the cattails, produce specialized support structures within their cells to cope with winds. This is great, especially when growing near a large, windy water source.

A team of researchers recently took a much closer look at the leaf cells of a variety of cattail species (genus Typha). For decades, there has been knowledge of fibers that traverse the air chambers within the cells. These have largely been ignored but as it turns out, they indeed serve a purpose.

(A) Longitudinal section showing the fibre cables anchored in diaphragms composed of aerenchyma tissue. (B) Longitudinal section showing the fibre cables anchored in diaphragms composed of aerenchyma tissue. (C) Cross section. The thick ventral (v)and dorsal (d) surfaces of the leaf are separated by thick partitions (P) that run the length of the leaf. Thin diaphragms (D) connected perpendicular to the thick partitionsare traversed by very fine fibre cables (FC), which are anchored to them. This construction has often been compared to sandwich-type construction, giving a low-density structure of high stiffness and strength (Rowlatt and Morshead, 1992)

As any good engineer will tell you, if a structure is to remain sound, it needs multiple avenues in which stress can be redistributed. The same goes for living structures like leaves. The fibers are arranged within the cells makes them quite strong under tension. In this way, multiple load paths are created to distribute the stress of high winds on the leaves. We like to take credit for most of our ideas but, time and again, nature beat us to it first.

Photo Credit: [1] [2]

Further Reading: [1]

What Are Plants Made Of?

Have you ever thought about what plants are made of? I mean, really thought about it. Strip away all the splendor and glory of all the different plant species on this planet and really take a close look at how plants grow and make more plants. It is a fascinating realm and it all has to do with photosynthesis. To go from photons given off by our nearest star to a full grown plant is quite the journey and, at the end of that journey, you may be surprised to learn what plants are all about.

It starts with photons. Leaving the sun they travel out into the universe. Some eventually collide with Earth and make their way to the surface. Plants position their leaves to absorb these photons. Energy from the photons is used to split water molecules inside the chloroplasts. In the process of splitting water, oxygen is released as a byproduct (thanks plants!). Splitting water also releases electrons and hydrogen ions.

These electrons and hydrogen ions are used to make energy in the form of ATP. Along with some electrons, ATP is then used in another cycle known as the Calvin cycle. The point of the Calvin cycle is to take in CO2 and use the energy created prior to reduce carbon molecules into chains of organic molecules. Most of the carbon in a plant comes from the intake of CO2. Through a series of steps (I will spare you the details) plants piece together carbon atoms into long chains. Some of these chains form glucose and some of that glucose gets linked together into cellulose.

Cellulose is the main structural component of plant cells. From the smallest plants in the world (genus Wolffia) all the way up to the largest and tallest redwoods and sequoias (incidentally some of the largest organisms to have ever existed on this planet) , all of them are built out of cellulose. So, in essence, all the plant life you see out there is literally built from the ground up by carbon originating from CO2 gas. Pretty incredible stuff, wouldn't you agree?

The Trumpet Creeper

Photo by beautifulcataya licensed under CC BY-NC-ND 2.0

With its impressive bulk and those stunning tubular red flowers, one would be excused for thinking that the trumpet creeper (Campsis radicans) was a tropical vine. Indeed, the family to which it belongs, Bignoniaceae, is largely tropical in its distribution. There are a handful of temperate representatives, however, and the trumpet creeper is one of the most popular. Its beauty aside, this plant is absolutely fascinating.

As many of you probably know, the trumpet creeper can reach massive proportions. In the garden, this can often result in collapsed structures as its weight and speed of growth is something few adequately prepare for. In the wild, I most often see this vine in somewhat disturbed forests, usually near a floodplain. As such, it is supremely adapted to take a hit and keep on growing year after year.

Photo by Maja Dumat licensed under CC BY 2.0

One of the many reasons this plant performs so well both where it is native and where it is not is that it recruits body guards. This is easy to witness in a garden setting as the branches and especially the flowers are frequently crawling with ants. Trumpet creepers trade food for protection via specialized organs called extrafloral nectaries. These structures secrete sugary nectar that is readily sucked up by tenacious ants. When a worker ant finds a vine, more workers are soon to follow. 

Amazingly for a temperate plant, trumpet creepers produce more extrafloral nectaries of all four categories - petiole, calyx, corolla, and fruit. What this means is that all of the important organs are covered in insects that viciously attack anything that might threaten this sugary food supply. Hassle one of these vines at your own peril. With its photosynthetic and reproductive structures protected, trumpet creepers make a nice living once established.

Photo by Salicyna licensed under CC BY-SA 4.0

Reproduction is another fascinating aspect of trumpet creeper biology. A closer inspection of the floral anatomy will reveal a bilobed stigma. Amazingly, this stigma has the ability to open and close as potential pollinators visit the flowers. Stigmatic movement in the trumpet creeper has attracted a bit of attention from researchers over the years. What is its function?

Evidence suggests that the opening and closing of the lobed stigma is way of increasing the chances of pollination. Touch alone is not enough to trigger the movement. However, when researchers dusted pollen onto the stigma, then it began to close. What's more, this action happens within 15 to 60 seconds. Amazingly, there appears to be a threshold to whether the stigma stays closed or reopens after 3 hours or so.

Photo by Jim Conrad (Public Domain)

It turns out, the threshold seems to depend on the amount of pollen being deposited. Only after 350 grains found their way onto the stigma did it close permanently. Experts feel that this a means by which the plant ensured ample seed set. If too few pollen grains end up on the stigma, the plant risks not having all of its ovules fertilized. By permanently closing after enough pollen grains are present, the plant can ensure that the pollen grains can germinate and fertilize the ovules without being brushed off.

It is interesting to note that the flowers frequently remain on the plant after they have been fertilized. This likely serves to maintain a largely floral display that continues to attract pollinators until most of the flowers have been pollinated. Speaking of pollinators, observations have revealed that the trumpet creeper is pollinated primarily by ruby-throated hummingbirds. Although insects like bumblebees frequently visit these blooms, bringing pollen with them in the process, hummingbirds, on average, bring and deposit 10 times as much pollen as any other visitor. And, considering the threshold on pollen mentioned above, trumpet creeper appears to have evolved a pollination syndrome with these lovely little birds.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3] [4]