A Common Plant With An Odd Pollination Mechanism

Photo by Kerry Woods licensed under CC BY-NC-ND 2.0

Pollination is not an altruistic enterprise. Each party involved is trying to maximize its gains while minimizing its losses. Needless to say, cheaters abound in natural systems. As such, plants have gone to great lengths to ensure that their reproductive investments pay off in the long run. Take, for instance, the case of the fragrant water-lily (Nymphaea odorata). 

Most of us have encountered this species at some point in our lives. Those who have often remark on the splendor of their floral displays. Certainly this is not lost on pollinators either. Coupled with their aromatic scent, these aquatic plants must surely be a boon to any insect looking for pollen and nectar. Still, the flowers of the fragrant water-lily take no chances.

Close observation will reveal an interesting pattern in the blooming cycle of this water-lily. On the first day that the flowers open, only the female portions are mature. The structure itself is bowl-like in shape. Filling this stigmatic bowl is a viscous liquid. After the first day, the flowers close for the evening and reopen to reveal that the stigma is no longer receptive and instead, the anthers have matured.

Many insects will visit these floating flowers throughout the blooming period. Everything from flies, to beetles, and various sorts of bees have been recorded. Seed set in this species is pollen limited so any insect visiting a female flower must deposit pollen if reproduction is to be achieved. This is where that bowl of sticky liquid comes into play. The liquid itself is rather unassuming until you see an insect fall in.

Photo by Matthew Beziat licensed under CC BY-NC 2.0

Due to the presence of surfactants, any insect that falls into the fluid immediately sinks to the bottom. The flowers seem primed to encourage this to happen too. The flexible inner stamens that surround the bowl bend under the weight of heavier insects, thus dumping them into the liquid below. Only by observing this process under extreme magnification does all of this make sense.

The liquid within the bowl essentially washes off any pollen that a visiting insect had stuck to its body. As the pollen falls off, it drifts down to the bottom of the bowl where it contacts the receptive stigma. Thus, cross-pollination is achieved. Most of the time, insect visitors are able to crawl out without any issue. However, the occasional insect will drown within the fluid. Alas, that is no sweat off the water-lily's back. Having dropped off the pollen it was carrying, it is of little use to that flower anymore.

Once a water-lily flower has been fertilized, its stem begins to curl up like a spring. This draws the ovaries underwater where they can develop in relative safety. It also ensures that, upon maturing, the seeds are more likely to find a suitable underwater site for germination. To think that this drama plays out time and time again unbeknownst to the casual observer is something I find endlessly fascinating about the natural world.

Photo Credit: [1] [2]

Further Reading: [1] [2]

The First Trees Ripped Themselves Apart To Grow

Illustration by Falconaumanni licensed under CC BY-SA 3.0

A new set of fossil discoveries show that the evolutionary arms race that are forests started with plants that literally had to rip themselves apart in their battle for the canopy. The first forests on this planet arose some 385 million years ago and were unlike anything we know today. They consisted of a clade of trees known scientifically as Cladoxylopsids, which have no living representatives in these modern times. How these trees lived and grew has remained a mystery since their fossilized trunks were first discovered but a new set of fossils from China reveals that these trees were unique in more ways than one.

Laying eyes on a full grown Cladoxylopsid would be a strange experience to say the least. Their oddly swollen base would gradually taper up a trunk that stretched some 10 to 12 meters (~30 - 40 feet) into a canopy of its relatives. They had no leaves either. Instead, their photosynthetic organs consisted of branch-like growths that were covered in twig-like projections. Whereas most fossils revealed great detail about their outward appearance, we have largely been in the dark on what their internal anatomy was like. Excitingly, a set of exquisitely preserved fossils from Xinjiang, China has changed that. What they reveal about these early trees is quite remarkable.

[SOURCE]

As it turns out, the trunks of these early trees were hollow. Unlike the trees we know today, whose xylem expands in concentric rings and forms a solid trunk, the trunk of Cladoxylopsid was made up of strands of xylem connected by a network of softer tissues. Each of these strands was like a mini tree in and of itself. Each strand formed its own concentric rings that gradually increased the size of the trunk. However, this gradual expansion did not appear to be a gentle process.

As these strands increased in size, the trunk would grow larger and larger. In doing so, the tissues connecting the strands were pulled tighter and tighter. Eventually they would tear under the strain. They would gradually repair themselves over time but the effect on the trunk was quite remarkable. In effect, the base of the tree would literally collapse in on itself in a controlled manner. You could say that older Cladoxylopsids developed a bit of a muffin top at their base. 

A cross section of a Cladoxylopsid trunk showing the hollow center, individual xylem strands, and the network of connective tissues. [SOURCE]

Although this seems very detrimental, the overall structure of the tree would have been sturdy. The authors liken this to the design of the Eiffel tower. Indeed, a hollow cylinder is actually stronger than a solid one of the same dimensions. When looked at in the context of all other trees, this form of growth is truly unique. No other trees are constructed in such a manner.

The authors speculate that this form of growth may be why these trees eventually went extinct. It would have taken a lot of energy to grow in that manner. It is possible that, as more efficient forms of growth were evolving, the Cladoxylopsids may not have been able to compete. It is anyone's guess at this point but this certainly offers a window back into the early days of tree growth. It also shows that there has always been more than one way to grow a tree.

LEARN MORE ABOUT THESE TREES AND THE FORESTS THEY MADE IN EPISODE 253 OF THE IN DEFENSE OF PLANTS PODCAST.

Photo Credits: [1] [2]

Further Reading: [1]

Bird Pollination Of The Bird Of Paradise

Public domain

Who hasn't stared in wonderment at the inflorescence of a bird of paradise? One doesn't need too much of an imagination to understand how these plants got this common name. Flowers, however, did not evolve in response to our aesthetic tastes. They are solely for sex and in the case of bird of paradise, Strelitzia reginae, pollination involves birds.

In its native range in South Africa, S. reginae is pollinated by sunbirds, primarily the Cape weaver (Ploceus capensis). That alluring floral morphology is wonderfully adapted to maximize the chances of successful cross-pollination by their avian visitors. Cape weavers are looking for a sip of energy rich nectar. To get at said nectar, the birds must perch on the inflorescence. Not any position will do either.

Photo by Forest & Kim Starr licensed under CC BY 3.0

To get their reward, the birds must perch so that their beaks are at just the right angle to reach down into the floral tubes. The plant ensures this by providing a convenient perch. Those fused blue petals are structurally reinforced and actually serve as a convenient perch! Upon alighting on the perch, the hidden anthers are thrust outward from their resting chamber, brushing up against the bird's feet in the process. The Cape weaver doesn't move around much once on the flower so self pollination is minimized.

When the bird visits another plant, the process is repeated and pollination is achieved. Seed set is severely pollen limited. This is a good thing considering how popular they are in cultivation. Plants growing outside of South Africa rarely set seed without a helping hand. However, here in North America, some birds seemed to have figured out how to get at bird of paradise nectar.

[SOURCE]

Observations made in southern California found that at least one species of warbler, the common yellowthroat (Geothlypis trichas), not only made regular visits to a stand of S. reginae, it also seemed to figure out the proper way to do so. Individuals were seen perching on the floral perch and drinking the nectar. They were pretty effective visitors at that. Of the 14,400 inflorescence found within the study area, 88% of them produced viable seed! It seems that far from its native range, S. reginae has a friend in at least one New World warbler. Armed with this knowledge, land owners should be vigilant to ensure this plant doesn't become a problem in climates suitable for its growth.

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

Further Reading: [1]

Appalachia

Welcome to Appalachia. I have fallen in love with this corner of the world in large part because of its wonderfully rich and unique flora. Join In Defense of Plants as we take a sneak peak at a mere fraction of the botanical riches these mountains hold.

Further Readings On Appalachian Flora:

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Of Acorns and Squirrels

I find it fun to watch squirrels frantically scurrying about during the fall. Their usually playful demeanor seems to have been replaced with more serious and directed undertones. If you watch squirrels close enough you may quickly realize that, when it comes to oaks, squirrels seem to have a knack for taxonomy. They quickly bury red oak acorns while immediately set to work on eating white oak acorns. Why is this?

Music by:
Artist: Botanist
Track: Stargazer
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In Search of Fall Flowering Gentians

Fall is bittersweet for avid botanizers but if you look around you, there are still flowers to be seen! Join us as we go in search of some of my favorite fall flowering species of Gentian.

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Track: Masters of Earth
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A Bat-Pollinated Passion Flower From Ecuador

[SOURCE]

Say "hello" to one of Passiflora's most recent additions, the bat-pollinated Passiflora unipetala. The first specimens of this vine were discovered back in 2009 by Nathan Muchhala while studying flower visiting bats in northern Ecuador. It is a peculiar member of the genus to say the least. 

One of the most remarkable features of this plant are its flowers. Unlike its multi-petaled cousins, this species stands out in producing a single large petal, which is unique for not only the genus, but the whole family as well. The petal is quite large and resembles a bright yellow roof covering the anthers and stigma. At the base of the flower sits the nectar chamber. The body of the plant consists of a vine that has been observed to grow upwards of 6 meters up into the canopy.

[SOURCE]

Flowering in this species occurs at night. Their large size, irregular funnel shape, and bright yellow coloring all point to a pollination syndrome with bats. Indeed, pollen of this species has been found on the fur of at least three different bat species. Multiple observations (pictured here) of bats visiting the flowers helped to confirm. Oddly enough for a bat-pollinated plant, the flowers produce no detectable odor whatsoever. However, another aspect of its unique floral morphology is worth noting. 

The surface of the flower has an undulating appearance. Also, the sepals themselves have lots of folds and indentations, including lots of dish-shaped pockets. It is thought that these might help the flower support the weight of visiting bats. They may also have special acoustic properties that help the bats locate the flowers via echolocation. Though this must be tested before we can say for sure, other plants have converged on a similar strategy (read here and here).

As it stands currently, Passiflora unipetala is endemic to only a couple high elevation cloud forests in northern Ecuador. It has only ever been found at two locations and sadly a landslide wiped out the type specimen from which the species description was made. As such, its introduction to the world came complete with a spot on the IUCN Redlist as critically endangered. Luckily, the two localities in which this species has been found are located on privately protected properties. Let's just hope more populations are discovered in the not-too-distant future.

Photo Credits: [1] 

Further Reading: [1]

Ants As Pollinators?

Photo by Ken-ichi Ueda licensed under CC BY-NC 2.0

Ants interact with plants in a variety of beneficial ways. They offer protection, they provide nutrients, they even disperse seeds! When it comes to pollination, however, plants have largely gone elsewhere. That's not to say ants don't get directly involved in the sex lives of plants. At least one plant species native to Spain has been found to be pollinated by ants. Certainly there are probably more examples of ant pollination throughout the plant kingdom, we simply have to look. For example, one possible ant-pollinated plant can be found growing on the west coast of North America.

The dwarf owl's-clover (Triphysaria pusilla) is a small annual member of the broomrape family. It really is a dwarf species, rarely exceeding a few inches in height. What it lacks in size, it makes up for in abundance. Large colonies of these species can be found growing among other low statured herbs in wetter areas like spring-fed grasslands. Their tendency to produce lots of anthocyanin pigments in their tissues means that these maroon colonies really stand out. Like other members of the family, it is a facultative hemiparasite, tapping into the roots of surrounding vegetation with its roots, stealing nutrients and water as the situation demands.

Photo by brewbooks licensed under CC BY-SA 2.0

Flowering in the dwarf owl's-clover is rather inconspicuous. The dense flowering spikes produce minute, tubular, maroon-yellow flowers. It has been observed that, at any given point during the flowering season, only three flowers will have matured on any given plant. Two of these flowers mature their anthers first whereas the remaining flower matures its stigma. This is likely an adaptation for increasing the chances of cross pollination. 

Photo by Richard Droker licensed under CC BY-NC-ND 2.0

Because these flowers hardly qualify as an attractive display for more commonly encountered insect pollinators, it has been hypothesized that ants are the preferred pollinator of this species. Early work even suggested that the dense leaf arrangement facilitates ant movement to and from flowers in any given colony. Although no one has yet quantified the efficacy of ants as pollinators of this species, numerous observations of ants visiting flowers and picking up pollen have been made. Famously, such a scene was filmed for the 1981 documentary "Sexual Encounters of the Floral Kind."

Whether these visits constitute effective pollination remains to be seen. It could be that the ants are nothing more than nectar and pollen thieves. What's more, many ants produce substances from specialized glands that, among other things, destroy pollen. Until someone takes the time to study this interaction, we simply do not know. Sounds like a fun research project to me! 

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

Further Reading: [1]

The Nitrogen-Fixing Abilities of Cycads

Photo by Daderot Public Domain

Long before the first legumes came onto the scene, the early ancestors of Cycads were hard at work fixing atmospheric nitrogen. However, they don't do this on their own. Despite being plentiful in Earth's atmosphere, gaseous nitrogen is not readily available to most forms of life. Only a special subset of organisms are capable of turning gaseous nitrogen into forms usable for life. Some of the first organisms to do this were the cyanobacteria, which has led them down the path towards symbioses with various plants on many occasions. 

Cycads are but one branch of the gymnosperm tree. Their lineage arose at some point between the Carboniferous and Permian eras. Throughout their history it would seem that Cycads have done quite well in poor soils. They owe this success to a partnership they struck up with cyanobacteria. Although it is impossible to say when exactly this happened, all extant cycads we know of today maintain this symbiotic relationship with these tiny prokaryotic organisms. 

Cross section of a coralloid cycad root showing the green cyanobacteria inside. Photo by George Shepherd licensed under CC BY-NC-SA 2.0

The relationship takes place in Cycad roots. Cycads don't germinate with cyanobacteria in tow. They must acquire them from their immediate environment. To do so, they begin forming specialized structures called precoralloid roots. Unlike other roots that generally grow downwards, these roots grow upwards. They must situate themselves in the upper layer of soil where enough light penetrates for cyanobacteria to photosynthesize.

The cyanobacteria enter into the precoralloid roots through tiny cracks and take up residence. This causes a change in root development. The Cycad then initiates their development into true coralloid roots, which will house the cyanobacteria from that point on. Cycads appear to be in full control of the relationship, dolling out carbohydrates in return for nitrogen depending on the demands of their environment. Coralloid roots can shed and reform throughout the lifetime of the plant. It is quite remarkable to think about how nitrogen-fixing symbiotic relationships between plants and microbes have evolved independently throughout the history of life on this planet.

Photo Credits: [1] [2]

Further Reading: [1] [2]

The Hidden Anatomy of Grass Flowers

Grass flowers have their own unique beauty. Examine them with a hand lens and a whole new world of angiosperm diversity suddenly opens up. Unlike other flowering plants, their charm lies not in showy sepals or petals, but in an intricacy centered around the utilization of wind for pollination. However, such floral organs are not lacking. Grass flowers do in fact produce a perianth, the function of which has been highly modified.

To see what I am referring to, you need to do some dissection under a scope. Pull off a flower and peel away the sheaths (the palea and lemma) that cover it. Inside you will see an ovary complete with feathery stigmas as well as the anthers. At the base of the ovary sits a pair of scales called lodicules. These lodicules are thought to be the rudimentary remains of the perianth. They certainly don't resemble sepals or petals but that is because the function of these structures is not to attract pollinators. They assist in pollination in another way.

Photo by Matt Lavin CC BY-SA 2.0

When grass flowers are ready for reproduction, the lodicules begin to swell. This swelling serves to push apart the rigid palea and lemma that protected the flowering parts as they developed. Once apart, the anthers and stigma are free to emerge and let wind do the dirty work for them. Lodicules differ quite a bit from species to species in their size, shape, and overall appearance. Much of this is likely tied to the overall structure in grass flowers.

Photo Credits: [1] [2]

Further Reading: [1]

Juicy Citrus

I was enjoying some citrus the other day when I got to thinking about these peculiar fruits. They are some of my favorites yet I know very little about their development. What is a citrus fruit exactly and why are they so juicy?

To start with, citrus fruits are produced by members of the citrus or rue family - Rutaceae. Not all members of this family produce them either. Technically speaking, the oranges, lemons, limes (etc.) we eat are specialized berries called "hesperidia." They are characterized by their tough rind and juicy interior.

Following fertilization, the ovary of each flower begins to swell. On the outside of the swelling fruit you find the rind or “pericarp.” The pericarp itself has a few layers associated with it but this is where the oil-filled pits are located. Anyone that has ever squeezed an orange peel has seen these pits spurt their contents.

Citrus australasica, the Australian finger lime or caviar lime. Photo by Amada44 licensed under CC BY-SA 3.0

Inward from the pericarp are a series of segments, which are the carpels. The individual carpels are the reason why oranges can be so easily segmented. Inside each carpel is a locule. These are small cavities where the seeds are housed. Lining the walls of these loculi are tiny hairs that, as the fruit matures, gradually fill with juices.

These juice-filled hairs makeup the pulp of a citrus fruit. Look closely and you can see that they are indeed individual compartments. This not only provides some nutrients to the developing seeds, it also provides a meal for potential seed dispersers, thus increasing the chances of successful recruitment away from the parent tree.

From a quick snack I spiraled into a world of new information. It is amazing what you can learn from simple questions. As a botanically oriented person, every meal offers a sea of discovery!

Photo Credit: [1] [2]

Further Reading: [1]

Arctic Foxes: The Unintentional Gardeners

Predators are an integral component of any healthy ecosystem. Their influence can even be felt at the botanical level via what are called top-down controls. Either through direct predation or through altering their behavior, predators influence the herbivores in any system, which usually results in healthier plant communities. This method is rather indirect but new evidence shows that in the Arctic tundra, a top predator is having quite a direct influence on plant communities.

What's not to love about Arctic foxes? All anthropomorphic views aside, Arctic foxes are important predators in this ecosystem. Although the food web complexity on the tundra is largely driven by limits to plant productivity, a paper published in 2016 shows that these little canids can have profound effects on vegetation. This doesn't have to do with predation directly but rather their reproductive behavior. 

Arctic foxes live, give birth, and raise their young in underground dens. Without these subterranean homes, the foxes would be much more vulnerable to other predators as well as the harsh Arctic climate. Dens don't happen overnight either. Suitable sites are tended for generations and some dens may well be more than a century old. All this equates to a lot of activity in and around a good den site. 

With an average litter size of 8 - 10 pups per female, one can imagine the food and waste buildup must be considerable. Like all predators, Arctic fox food and waste are rich in nitrogen and phosphorus compounds, the necessary building blocks of life. Many an onlooker has noticed that, unsurprisingly, plant growth around Arctic fox dens is much more lush than on the surrounding landscape. Until recently though, such differences have hardly been quantified.

Arctic Fox (Vulpes lagopus) photo by Allan Hopkins licensed under CC BY-NC-ND 2.0

By examining the soil and plant characteristics around Artic fox dens in Canada and comparing these data to surrounding sites without Arctic fox dens, a team of researchers put the first comprehensive numbers to the effects of Arctic foxes on tundra plant communities. They found that soils from in and around Arctic fox dens contained significantly higher levels of nitrogen and phosphorus than did the surrounding control plots. What's more, these levels varied throughout the year. In June, for instance, soil nitrogen and phosphorus levels were 71% and 1195% higher than non-den soils. These levels seemed to switch later in the summer. In August, soil nitrogen from fox dens were 242% higher and soil phosphorus levels were 191% higher.

As you can probably imagine, all of these extra nutrients caused a change in vegetation around the dens. Den sites were far more productive in terms of vegetation. The team found that, on average, Arctic fox dens supported 2.8 times more plant biomass than did the surrounding area. The authors note that these were conservative estimates and that the true values are much higher. Taken together, these results demonstrate that far from simply being top predators, Arctic foxes are true ecosystem engineers, at least on local scales. This is especially important in such a demanding ecosystem as the Arctic tundra.

Photo Credits: [1] [2]

Further Reading: [1]

Meet the Sweetfern

Photo by Sten Porse licensed under CC BY-SA 3.0

I remember the first time I laid my eyes on Comptonia peregrina. I was new to botany at that point in my life so I didn't have a well developed search image for these sorts of things. I was scrambling down a dry ridge with a scattered overstory of gnarly looking chestnut oaks when I saw a streak of green just below me on a sandy outcropping. They were odd looking plants, the likes of which I had never seen before.

I took out my binoculars to get a better look. What were these strange organisms? Were they ferns? No, they seemed to have woody stems. Were they gymnosperms? No, I could make out what appeared to be male catkins. Luckily I never leave home without a field guide or two. Using what little terminology I knew, I was able to narrow my focus to a plant commonly called a "sweetfern."

Photo by Megan Hansen licensed under CC BY-SA 2.0

This was one of the first instances in which I grasped just how troublesome common names can be. C. peregrina is mostly definitely not a fern. It is actually an angiosperm that hails from the bay family (Myricaceae). Comptonia is a monotypic genus, with C. peregrina being the only species. It is a denizen of dry, nutrient poor habitats. As such, it has some wonderful adaptations to deal with these conditions.

To start with, its a nitrogen fixer. Similar to legumes, it forms nodules on its roots that house specialized nitrogen-fixing bacteria called rhizobia. This partnership takes care of its nitrogen needs, but what about others? One study found that not only do the roots form nodules, they also form dense cluster roots. Oddly, closer observation found that these clusters were not associated with mycorrhizal fungi. What's more, they also found that these structures were most prevalent in highly disturbed soils. It is thought that this is one way that the plant can maximize its uptake of phosphorus under the harshest growing conditions. 

View fullsize

Photo by Jomegat licensed under CC BY-SA 3.0

Flowering in this species is not a showy event. C. peregrina can be monoecious or dioecious, producing male and female catkins towards the ends of its shoots. After fertilization, seeds develop inside bristly fruits. Seed banking appears to be an important reproductive strategy for this species. One study found that germinated seeds had lain dormant in the soil for over 70 years until disturbance opened up the canopy above. It is expected that seeds of this species could exhibit dormancy periods of a century or more. 

In total, this is one spectacular species. Not only does it have a unique appearance, it is also extremely hardy and an excellent species to plant in drought-prone soils wherever it is native. I do see it in landscaping from time to time. If you encounter this species in the wild, take the time to observe it in detail. You will be happy you did!

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

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

Delayed Greening

It goes without saying that leaves are vital to the existence of any photosynthetic plant. They are, after all, the food making organs. This is why plants go to great lengths to protect them. Losing leaves can be extremely costly. One of the most intriguing methods of anti-herbivory in plants is known as delayed greening. Flushes of new growth bathed in reds, whites, and light greens can color forests from top to bottom. 

Delayed greening is a matter of resource conservation and herbivore protection. The cellular machinery that makes photosynthesis possible is costly to produce. It requires large amounts of nutrients, such as nitrogen and phosphorus, that are often in short supply. If a plant can help it, its best to avoid losing a leaf chock full of these precious materials. Delayed greening does just that. 

Photo by T.Voekler licensed under CC BY-SA 3.0

Essentially, the process proceeds exactly as it sounds. Young shoots and leaves gradually expand over time, becoming more green as they grow tougher and better defended. When a plant packs its leaves full of photosynthetic machinery right out of the gates, when leaves are small and tender, it runs the risk of loosing all of its investment to a hungry herbivore. In contrast, non-photosynthetic leaves are thought to be less palatable to herbivores because they simply do not have the nutritional content of photosynthetic leaves.

By delaying the development of chlorophyll until the leaf is fully expanded and a bit tougher, some plants are maximizing the chances of successfully increasing their photosynthetic capacity over time. Research has shown that plants that exhibit the delayed greening strategy experience significant reductions in the amount of herbivory over time. What they lose with the lack of photosynthesis early on they make up for in the fact that such leaves last longer.  

Photo Credits: [1] [2]

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

Botanical Gardens & Plant Conservation

Botanical gardens are among my favorite places in the world. I find them both relaxing and stimulating, offering something for all of our senses. Botanical gardens are valuable for more than just their beauty. They serve a deeper purpose than simply showcasing endless poinsettia varieties or yet another collection of Dale Chihuly pieces (a phenomenon I can't quite wrap my head around). Botanical gardens are vitally important centers of ex situ plant conservation efforts.

Ex situ conservation literally means "off site conservation," when plants are grown within the confines of a botanical garden, often far away from their native habitats. This is an important process in and of its own because housing plants in different locations safeguards them from complete annihilation. Simply put, don't put all your endangered eggs in one basket.

I don't think botanical gardens get enough credit for their conservation efforts. Sadly, such endeavors are often overshadowed. That's not to say we don't have a good handle on what is going on. In fact, a study published in August of 2017 looked at the status of ex situ plant conservation efforts around the globe.

The paper outlines a conservative estimate of the diversity of plants found in botanical gardens and highlights areas in desperate need of improvement. Utilizing a dataset compiled by Botanic Gardens Conservation International (BGCI), the team found that the world's botanical gardens contain somewhere around 30% or 105,209 of the 350,699 plant species currently known to science. In total, they estimate humanities various living collections contain representatives from roughly 90% of the known plant families. That is pretty impressive considering the scale of plant diversity on our planet.

Proportions of the world's plants represented in botanical garden collections (Source)

Their research didn't stop there either. The team dove deeper into these numbers and found that there are some serious discrepancies in these estimates. For instance (and to my surprise), botanical gardens house more temperate plant species than they do tropical plant species. They estimated that nearly 60% of the world's temperate plant species are being grown in botanical gardens around the world but only 25% of tropical species. This is despite the fact that most of the world's plants are, in fact, tropical.

Similarly, only 5% of botanical garden collections are dedicated to non-vascular plants like mosses and liverworts. This is a shame not only because these plants are quite interesting and beautiful, but they also are descendants of the first plant lineages to make their way onto land. They are vital to understanding plant evolution as well as plant diversity.

Orchid conservation at the Atlanta Botanical Garden (learn more)

As I mentioned above, ex situ conservation efforts are critical in fighting plant extinctions across the globe. With 1/5 of the world's plants at risk of extinction, the authors of the paper were particularly interested in how botanical gardens were doing in this regard. They found that although various institutions are growing nearly half of all the known threatened plant species on this planet, only 10% of their collection space is devoted to these species. It goes without saying that this number needs to improve if we are to stave off further extinctions.

Taken together, this study paints an interesting and informative picture of botanical garden collections on a global scale. They are doing amazing work to protect and showcase plant diversity. However, there is always a need for improvement. More space and effort needs to be made in ex situ plant conservation efforts. More plants, especially little known tropical species, need to be brought into cultivation. More space must be devoted to propagating threatened and endangered species. Finally, more attention must be given to natural plant diversity rather than gaudy cultivars. If you love botanical gardens as much as I do, please support them. As the authors so eloquently summarize, "Without deep sustained public support, the plant conservation movement will struggle."

Further Reading: [1]

Evidence Of Carnivory In Teasel

Photo by Isidre blanc licensed under CC BY-SA 4.0

As far as carnivorous plants are concerned, the common teasel (Dipsacus fullonum) seems like a strange fit. Observe this plant up close, however, and you might notice something interesting. Its leaves are perfoliate and form a cup-like depression where they attach to the main stem. Not only does this cup regularly fill with water, it also frequently traps small insects.

Many have speculated over the function of this anatomical trap. Much of this speculation has centered around the idea that it may serve as a form of protection for the flowers located above. Insect herbivores climbing up the stem in search of food instead find a moat of water. Some inevitably fall in and drown in the process. Other hypotheses have been put forward as well including the possibility of something approaching carnivory. 

The idea that common teasel could be, to some degree, carnivorous never really went away. For most of this time it has remained entirely theoretical. There simply was no empirical evidence available to say otherwise. All of that changed with a 2011 study published in PLOS. A research duo finally put this theory to the test in the first ever experiment to see if teasel gains any sort of nutrient benefit from its insect victims.

Dipsacus fullonum (Wild Teasel, Common Teasel). Rainwater is held back in leaves. Photo by Björn Appel licensed under CC BY-SA 3.0

By systematically supplying teasel plants with insect prey, the team was able to look at how plants responded to the addition of a potential meal. They added various levels of insect larvae to some plants and removed them from others. For their study, evidence would come in the form of some sort of physiological response to the feeding treatments. If teasel really is obtaining nutrients from its insect victims, it stands to reason that those nutrients would be allocated to either growth or reproduction.

The resulting data offers the first evidence that teasel may in fact be benefiting from the insect carcasses. Although the team found no evidence that plants supplemented with insects were increasing in overall biomass, they did see a positive effect on not only the number of seeds produced but also their size. In other words, when fed a diet of insects, the plants weren't growing any larger but they were producing larger amounts of heavier seeds. This is a real boon for a plant with a biennial life cycle like teasel. The more healthy seeds they can produce, the better.

As exciting as these finds are, one must temper their expectations. As the authors themselves state in their paper, these findings must be replicated in order to say for certain that the effects they measured were due to the addition of insect prey. Second, no chemical analyses were made to determine if the plants are actively digesting these insects or even how available nutrients may be absorbed. Simply put, more work is needed. Perhaps teasel is a species that, evolutionary speaking, is on its way to becoming a true carnivore. We still can't say for sure. Nonetheless, they have given us the first evidence in support of a theory that went more than a century without testing. It is interesting to think that there is a strong possibility that if someone wants to see a carnivorous plant, they need go no further than a fallow field.

Photo Credits: [1] [2]

Further Reading: [1]

Red or White?

Photo by Msact at English Wikipedia licensed under CC BY-SA 3.0

Who doesn't love a nice oak tree? One cannot overstate their importance both ecologically and culturally. Although picking an oak tree out of a lineup is something many of us are capable of doing, identifying oaks to species can be a bit more challenging. This is further complicated by the fact that oaks often hybridize. Still, it is likely you have come across some useful tips and tricks for narrowing down your oak choices. One such trick is distinguishing between the red oaks and the white oaks. If you're anything like me, this is something you took for granted for a while. Is there anything biologically or ecologically meaningful to such a split?

In short, yes. However, a true appreciation of these groups requires a deeper look. To start with, oaks are members of the genus Quercus, which belongs in the family Fagaceae. Globally there are approximately 400 species of oak and each falls into one of three categories - the red oaks (section Lobatae), the white oaks (section Quercus), and the so-called "intermediate" oaks (section Protoblanus). For the sake of this article, I will only be focusing on the red and white groups as that is where most of the oak species reside. The intermediate oak group is made up of 5 species, all of which are native to the southwestern United States and northwestern Mexico.

As is common with oak identification, reliable techniques for distinguishing between the two groups can be tricky. Probably the most reliable feature is located on the inner surface of the acorn cap. In white oaks, it is hairless or nearly so, whereas in red oaks, it is covered in tiny hairs. Another useful acorn feature is the length of time it takes them to germinate. White oak acorns mature in one season and germinate in the fall. As such, they contain lower levels of tannins. Red oak acorns (as well as those of the intermediate group) generally take at least two seasons to mature and therefore germinate the following spring. Because of this, red oak acorns have a much higher tannin content. For more information on why this is the case, read this article.

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Tyloses in white oak xylem. Photo by Dr. Michael Rosenthal, Technische Universität Dresden via Rosenthal, M.; Bäucker, E. (2013): Zur Anatomie des Holzes der Weiß-Eichen. Rasterelektronenmikroskopische Bildtafeln zu den drei holzanatomischen Schnittrichtungen. licensed under CC BY-SA 3.0

Less apparent than acorns is the difference in the wood of red and white oaks. The wood of white oaks contains tiny structures in their xylem tissues called tyloses. These are absent from the wood of red oaks. The function of tyloses are quite interesting. During extreme drought or in the case of some sort of infection, they cut off regions of the xylem to stop the spread of an embolism or whatever may be infecting the tree. As such, white oaks tend to be more rot and drought resistant. Fun fact, tyloses are the main reason why white oak is used for making wine and bourbon barrels as it keeps them from leaking their contents.

More apparent to the casual observer, however, is leaf shape. In general, the white oaks produce leaves that have rounded lobes, whereas the red oaks generally exhibit pointed lobes with a tiny bristle on their tips. At this point you may be asking where an unlobed species like shingle oak (Quercus imbricaria) fits in. Look at the tip of its leaf and you will see a small bristle, which means its a member of the red oak group. Similarly, the buds of these two groups often differ in their overall shape. White oak buds tend to be smaller and often have blunted tips whereas the buds of red oaks are generally larger and often pointed.

Tricky leaves of the shingle oak (Quercus imbricaria). Note the bristle tip! Photo by Greg Blick licensed under CC BY-NC-ND 2.0

Despite this broad generalizations, exceptions abound. This is further complicated by the fact that many species will readily hybridize. Quercus is, after all, a massive genus. Regardless, oaks are wonderful species chock full of ecological and cultural value. Still, oak appreciation is something we all need more of in our lives. I encourage you to try some oak identification of your own. Get outside and see if you can use any of these tricks to help you identify some of the oaks in your neighborhood.

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

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

More to Tall Boneset Than Meets the Eye

For most of the growing season, tall boneset (Eupatorium altissimum) is largely overlooked. When it comes time to flower, however, it is impossible to miss. Contrasted against a sea of goldenrods, its bright white flowers really stand out. This is a hardy species, tolerating lots of sun and dry soils. It is also a boon for pollinators and is usually humming with attention. To the naked eye, it would seem that there is nothing strange going on with this species. It grows, flowers, and sets seed year after year. However, a gene’s eye view of tall boneset tells a vastly different story. 

A population-wide study revealed that the vast majority of the tall boneset plants we encounter are made up entirely of females. In fact, only populations found in the Ozark Mountains were found to produce sexually viable flowers with male and female organs. This is fascinating considering how wide spread this species is in North America. A close examination of the genome revealed that sexual plants were genetically diploid whereas the female-only plants were genetically triploid. These triploid plants produce sterile male parts that either have highly deformed pollen grains or produce no pollen at all. 

Sexual populations of tall boneset do not reproduce vegetatively. They must be cross pollinated in order to set seed. Such is not the case for the female-only populations. These plants set seed on their own without any pollen entering into the equation. The seeds they produce are essentially clones of the mother plant. Such asexual reproduction seems to be very advantageous for these plants. For starters, they produce considerably more seed than their sexually reproducing relatives. The offspring produced from those seeds, having the same genetic makeup as their mothers, are inherently well-adapted to whatever conditions their mothers were growing in. As such, populations can readily colonize and expand, which goes a long way in explaining the female-only dominance. 

Although tall boneset really hits its stride in midwestern North America, it can be found growing throughout the eastern portion of this continent. Casual observation would never reveal such interesting population dynamics which is why single species studies are so important. Not only do we learn that much more about a beloved plant, we also gain an understanding of how plants evolve over time as well as factors one must consider should conservation measures ever need to be considered. 

Further Reading: [1] 

Understanding the Cocklebur

Photo by Dinesh Valke from Thane, India licensed under CC BY-SA 2.0

Spend enough time in disturbed areas and you will certainly cross paths with a cocklebur (Xanthium strumarium). As anyone with a dog can tell you, this plant has no problems getting around. It is such a common occurrence in my life that I honestly never stopped long enough to think about its place on the taxonomic tree. I always assumed it was a cousin of the amaranths. You can imagine my surprise then when I recently learned that this hardy species is actually a member of the sunflower family (Asteraceae). 

Cocklebur doesn't seem to fit with most of its composite relatives. For starters, its flowers are not all clustered together into a single flower head. Instead, male and female flowers are borne separately on the same plant. Male flower clusters are produced at the top of the flowering stem. Being wind pollinated, they quickly dump mass quantities of pollen into the air and wither away. The female flowers are clustered lower on the stem and consist of two pistillate florets situated atop a cluster of spiny bracts. 

After fertilization, these bracts swell to form the burs that so many of us have had to dig out of the fur of our loved ones. Inside that bur resides the seeds. Cocklebur is a bit strange in the seed department as well. Instead of producing multiple seeds complete with hairy parachutes, the cocklebur produces two relatively large seeds within each bur. There is a "top" seed, which sits along the curved, convex side of the bur, and a "bottom" seed that sits along the inner flat surface of the bur. Studies performed over a century ago demonstrated that these two seeds are quite important in maintaining cocklebur on the landscape. 

Photo by Dinesh Valke from Thane, India licensed under CC BY-SA 2.0

You see, cocklebur is an annual. It only has one season to germinate, grow, flower, and produce the next generation. We often think of annual plants as being hardy but in reality, they are often a bit picky about when and where they will grow. For that reason, seed banking is super important. Not every year will produce favorable growing conditions so dormant seeds lying in the soil act as an insurance policy. 

Whereas the bottom seed germinates within a year and maintains the plants presence when times are good, the top seed appears to have a much longer dormancy period. These long-lived seeds can sit in the soil for decades before they decide to germinate. Before humans, when disturbance regimes were a lot less hectic, this strategy likely assured that cocklebur would manage to stick around in any given area for the long term. Whereas fast germinating seeds might have been killed off, the seeds within the seed bank could pop up whenever favorable conditions finally presented themselves. 

Today cocklebur seems to be over-insured. It is a common weed anywhere soil disturbance produces bare soils with poor drainage. The plant seems equally at home growing along scoured stream banks as it does roadsides and farm fields. It is an incredibly plastic species, tuning its growth habit to best fit whatever conditions come its way. As a result, numerous subspecies, varieties, and types have been described over the years but most are not recognized in any serious fashion. 

Sadly, cocklebur can become the villain as its burs get hopelessly tangled in hair and fur. Also, every part of the plant is extremely toxic to mammals. This plant has caused many a death in both livestock and humans. It is an ironic situation to consider that we are so good at creating the exact kind of conditions needed for this species to thrive. Love it or hate it, it is a plant worth some respect. 

Photo Credits: [1] [2] 

Further Reading: [1] [2]

So Many Goldenrods, So Little Time

Nothing says late summer quite like the blooming of the goldenrods. These conspicuous members of the aster family get a bad rap because many folks blame them for causing hay fever. This is simply not true! In this video we take a closer look at a small handful of goldenrods as a way of celebrating this ecologically important group.

Music by: Artist: Ampacity

Track: Encounter One

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