Your string of pearls (and its cousins) are all members of the daisy family

Photo by LynnK827 licensed by CC BY-NC-ND 2.0

I love the spike in popularity of houseplants. The more popular indoor gardening becomes, the more plants become available for obsessive growers such as myself. If you are like me, then learning about the ecological and evolutionary history of the plants you keep makes them all the more special. Take, for instance, a small group of scrambling succulents affectionately referred to as “string of pearls,” “string of bananas,” and “string of tears.” These all make incredible houseplants if given the proper care, but they become all the more interesting when you realize that they are distant cousins of the dandelions growing in your yard.

That’s right, each of these species are highly derived members of the daisy family (Asteraceae). Their taxonomy has been a bit wonky over the years. When I first took interest in these succulents, they resided in the genus Senecio. Some authors have suggested moving them into the genus Kleinia or Cacalia, but current systematics suggests they belong in a genus of their own - Curio. Inspection of the relationships within this group reveals that closely related species have evolved slightly different growing habits. The plants I will be focusing on for this article each resemble creeping vines but many of their close relatives are less vine-like but nonetheless still creep along the ground. For the sake of this piece, I am going to stick with the genus Senecio because, regardless of their taxonomic placement, the “sting of” clade is super fascinating from an ecological standpoint.

Senecio citriformis photo by Salchuiwt licensed by CC BY-SA 2.0

Senecio radicans photo by KENPEI licensed by CC BY-SA 3.0

All of these stringy plants hail from arid regions of South Africa. In the wild, they mostly scramble over rocks and bushes, often emerging out of cracks in rock in search of the right microclimate. Their oddly shaped, succulent leaves are an evolutionary adaptation to the tough conditions in which they evolved. The most leaf-like anatomy belongs to that of the string of bananas (S. radicans). Each leaf of S. radicans is shaped like a tiny green banana. More extreme versions of leaf morphology are found in the string of tears (S. citriformis) and string of pearls (S. rowleyanus & S. herreianus). The leaves of these three species resemble peas in shape, size and color. The leaves of S. rowleyanus are more spherical in shape (pearls), whereas the leaves of S. citriformis taper towards the tip (tears).

Senecio herreianus photo by Frank Vincentz licensed by CC BY-SA 3.0

Though all of these species grow in dry habitats, the more spherical shaped leaves of S. rowleyanus and S. citriformis are thought to be best adapted for drought. In growing spherical leaves, these plants are taking advantage of the surface area to volume ratio of a sphere. The benefit of this is that these species are able to maximize water storage while minimizing the amount of leaf surface exposed to the blistering sun. This way the leaves are able to maintain high levels of photosynthesis without overheating, all the while reducing leaf temperature.

In each of these species, the surface or adaxial side of the leaf exhibits a translucent window that runs the length of the leaf. It has long been hypothesized that leaf windows allow light to transmit into deep into the interior of the leaf where the photosynthetic machinery resides. More recent experiments on window-leaved succulents suggests that reality is not that simple. Instead, these windowed surfaces appear to allow the plant to maintain healthy levels of photosynthesis without the damaging their leaves via overheating.

Photo by Frank Vincentz licensed by CC BY-SA 3.0

When plants reach maturity, flowering can be prolific. Thin stems topped with tiny composite heads of cream-colored flowers erupt from the mat of vegetation. Then and only then do these plants readily reveal their placement within the daisy family. The inflorescence is made up entirely of discoid flowers. There are no rays like that of a sunflower. The flowers themselves are said to produce a pleasant odor frequently described as sweet and spicy. After pollination, the flowers give way to seeds topped with a parachute-like pappus that will carry them far and wide on the wind.

Learning about the natural history of these plants has given me a whole new appreciation of these strange, succulent members of the daisy family. What’s more, there is a whole world of succulent asters out there (a post for a later time) and many of them are equally as fascinating and beautiful.

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

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

Twinflower

Here is a short story about my first encounter with twinflower (Linnaea borealis) back in fall of 2014.

"Summer and occasionally fall" is all I needed to read. So, I had a chance after all. After a few days of sitting in a kayak, musing over various wetland plants, I was excited to get my feet back on solid ground. The Adirondack Mountains offer seemingly endless opportunities for botanizers (and all nature nuts really) to meet new and exciting species that aren't often seen. For me, Linnaea borealis is such a species.

Commonly referred to as twinflower, this small plant is technically a dwarf shrub. In fact, it is a member of the honeysuckle family, Caprifoliaceae. Unlike its larger, more aggressive cousins, twinflower would be an easy plant to miss for most. It behaves much like partridge berry as it ambles over rocks and logs, never leaving the damp forest floor. Out of those who would pay it any mind, even fewer would consider this nondescript plant much to fuss about but those people have never seen this plant in flower.

During the warmer summer months, L. borealis puts on an unbelievable display. Each sprig of stem and leaves throws up a pair of bell-like flowers that will knock your socks off. Each flower is permanently aimed at the ground like tiny lampshades. The flowers are small and dressed in a mixture of white and pink but a large population in full bloom would be impossible to miss. There is something to be said about the beauty of small plants like this. Unlike larger, gaudy flowers, L. borealis forces its admirers to get down on its level to enjoy its full beauty. I like that in a plant.

Twinflower ambling over a rock in the company of some Cladonia lichen.

The genus name "Linnaea" was given to this species in honor of the Swedish botanist, physician, and zoologist, Carl Linnaeus, who invented the binomial nomenclature naming scheme that we still use today. L. borealis has been said to be his favorite plant. As the specific epithet suggests, this species is circumboreal in its distribution. It is found in the northern forested regions of every continent in the northern hemisphere. It can also be found farther south but only at high elevation. These southern populations are disjunct relicts of the Pleistocene Epoch.

Pushed south by advancing ice sheets, boreal species like L. borealis took refuge at high elevation where climates were more similar to the far north. After the glaciers retreated, these populations were able to hang on in small pockets atop mountains. The most interesting thing about this is that L. borealis is not self compatible. It needs genetically different individuals to successfully set seed. In areas where only a small group of individuals represent an entire population, L. borealis has a hard time reproducing sexually. Such populations populations only persist via vegetative cloning. In places like Scotland, this has lead to some concern over genetic stagnation. Throughout the world, at the edges of its range, L. borealis has taken a hit from this genetic stagnation and its range is shrinking. As favorable climates continue to change, the relict populations atop mountains have nowhere to go and thus risk extirpation.

Despite all of this, L. borealis is one tough cookie. If you live where this plant is native, make sure to keep a watchful eye out for it when you are hiking. All too often it is trampled over by unwary hikers. If you are lucky enough to find a patch in bloom, get down on your hands and knees and really get to know this species. You will certainly be happy that you did.

Further Reading: [1] [2]

An Intriguing Way of Presenting One's Pollen

Photo by Monteregina (Nicole) licensed by CC BY-NC-SA 2.0

Getting pollen from one flower to another is the main reason why flowers exist in the first place. It makes sense then why pollen is often made readily available to pollinators. For many flowering plants, this means directing the pollen-filled anthers outward where they are ready to take advantage of floral visitors. The sunflower family (Asteraceae) does this a bit differently than most. They utilize a technique called secondary pollen presentation.

Though secondary pollen presentation is not unique to the sunflower family, their abundance on the landscape makes it super easy to observe. For the sunflower family, what looks like a single flower is actually an inflorescence made up of dense clusters of individual flowers. Each individual flower is roughly tubular in shape and, oddly enough, the anthers are tucked inside the tube facing the interior of the flower. It may seem odd to hide the anthers and their pollen inside of a tube until you see the blooming process sped up.

Photo by László Németh licensed by CC BY-SA 3.0

The sunflower family actually relies on the female parts of the flower to bring the pollen out from the floral tube and into the environment where pollinators can access it. Members of the sunflower family are protandrous, meaning the male parts mature before the female parts. What this means is that the style of the flower can be involved in presenting pollen before it becomes receptive to pollen. This allows enough time for pollen presentation and reduces the likelihood of self pollination.

As the style elongates within the floral tube, one of two things can happen with the pollen inside. In some cases, the style acts like a tiny piston, literally pushing the pollen out into the world. In other cases, the style is covered in tiny, brush-like hairs that rake the pollen from the sides of the floral tube and carry it out as it emerges. In both cases, the style remains closed until enough time has passed for pollen to be taken away from the inflorescence.

Watch _asteraceae GIF on Gfycat. Discover more Timelapse, aster, awesome, back, background, bloom, cool, flower, ground, grow, lapse, out, relax, slender, slow, time, visuals, white, wood, zone GIFs on Gfycat

After a period of time (which varies from species to species), the style splits at the tip and each side curls back on itself to reveal the stigmatic surface. Only at this point in time is are the female parts of the flower mature and ready to receive pollen. With any luck, much of the flowers own pollen would have been collected and taken away to other plants.

The combination of sequential blooming of individual flowers and protandry mean that members of the sunflower family both maximize their chances of pollination and reduce the likelihood of inbreeding. Add to that their ability to disperse their seeds great distances and myriad defense strategies and it should come as no surprise that this family is so darn successful. Get outside and try to witness secondary pollen presentation for yourself. Armed with a hand lens, you will unlock a world of evolutionary wonders!

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

Further Reading: [1] [2]

Let's Talk About Recruitment

Photo by --Tico-- licensed by CC BY-NC-ND 2.0

For any species to be considered successful, it must replace itself generation after generation. We call this process recruitment and it is very important. After all, reproduction is arguably the most fundamental aspect of life in a Darwinian sense. For plants, this can be done either vegetatively or sexually via seeds and spores. Though vegetative reproduction is a fundamental process for many plants around the globe, seed or spore germination is arguably the most important. To truly understand what a plant needs, we have to understand its germination requirements.

Recruitment is a considerable limiting factor for plant populations. In fact, it is the first major bottleneck plants must pass through. It is estimated that a majority of plant mortality occurs during the germination and seedling stages. However, not all plants are equal in this way. Some plants are considered seed or propagule limited whereas others are habitat limited.

If a plant is seed limited, it means that its ability to expand its population or colonize new habitats its limited by the ability of seeds (or spores) to make it to a new location. Once there, nature takes its course and germination occurs with little impediment. If a plant is habitat limited, however, things get a bit more tricky. For habitat limited plants, simply getting seeds to a new location is not enough. Some other aspect of the environment (soil moisture, texture, temperature, disturbance, etc.) limit successful germination. Only when the right conditions are present can habitat limited plants germinate and begin to grow.

Habitat limitation is probably the most common limit to plant establishment. Simply put, not all plants will be successful everywhere. Even the successful growth and persistence of adult plants can be poor predictors of seedling success. Many plants can live for decades or even centuries and the conditions that were present when they germinated may have long since changed. Even the presence of the adults themselves can make a site unsuitable for germination. Think of all of those fire adapted species out there that require the entire community to burn before their seeds will ever germinate.

In reality, it is likely that most plants are habitat limited to some degree. These are not binary categories after all, rather they are aligned along a spectrum of possibilities. The fact that most plants don’t completely take over an area once seeds or spores arrive is proof of the myriad limits to plant establishment. As such, recruitment limitation is extremely important to study. It can make a huge difference in the context of conservation and restoration. Even the successful establishment of adult plants is no guarantee that seedlings stand a chance. Without successful recruitment, all you have left is a nice garden that is doomed to run its course. By understanding the limits to plant recruitment, we can do much more than just improve on our ability to protect and bolster plant populations, we can also gain insights into why so many plants remain rare on the landscape and so few ever rise to dominance.

Photo Credits: [1]

Further Reading: [1] [2]

The Round Leaved Orchid

In the northern temperate regions of North America, late June marks the beginning of what I like to call orchid season. If you're lucky you may stumble across one of these rare beauties in full bloom. Their diversity in shape and size are mainly a result of the intricate evolutionary relationships they have formed with their pollinators. I spend much of my time botanizing trying to locate and photograph these botanical curiosities and any time I get to meet a new species is a very special time indeed. 

Take the round leaved orchid (Platanthera orbiculata) for example. For years I have only known this species as two round leaves that are slightly reminiscent of the phaleanopsis orchids you see for sale in nurseries and grocery stores. The leaves can be quite large too. With their glossy appearance, they are the easiest way to locate this plant.

When conditions are right and the plants have enough stored energy they will begin to flower. Rising from the middle of the pair of leaves is a decent sized inflorescence loaded with greenish white flowers. The flowers are interesting structures. Not particularly colorful, they have a long white lip and considerable green nectar spurs. There are said to be two varieties of this species, each being characterized by the length of the nectar spur. Unlike many orchids that offer no reward to pollinators, P. orbiculata produces nectar. The flowers are pollinated by noctuid moths, which is probably why they are white in color. Whereas most lepidopteran pollinated orchid attach their pollinia to the proboscis of the butterfly or moth, P. orbiculata attaches its pollinia to the eyes of visiting moths. 

If this isn't strange enough, the pollinia themselves have some of their own intriguing adaptations. Visiting moths take a certain amount of time to successfully access the nectar from the nectar spur. If the plant is to avoid wasting precious pollen on itself, then it must find a way to delay this process. The pollinia are the solution to this. When first attached to the eyes, the pollinia stick straight up. This keeps them away from the female parts of the plant as the moth feeds. Only after enough time has elapsed will the stalks of the pollinia begin to bend forward. At this point the moth will hopefully have moved on to the flowers of an unrelated individual. Pointing straight forward, they are now perfectly positioned to transfer pollen. 

Like all orchids, P. orbiculata relies on specialized mycorrhizal fungi for germination and survival. At the beginning of its life, P. orbiculata relies solely on the fungi for sustenance. Once it has enough energy to produce leaves it will repay the fungi by providing carbohydrates. However, the relationship is not over at this point. Every spring, P. orbiculata produces a new set of leaves as well as a whole new root system. The fungi supply a lot of energy for this process and if the plant is disturbed (ie. dug up by greedy poachers) or browsed upon, it is likely that it will not recover from the stress and it will die. The mycorrhizal fungi it relies on live on rotting wood so finding well rotted logs is a good place to start searching for this species. With declining populations throughout much of its range, it is important to remember to enjoy it where it grows. Leave wild orchids in the wild!

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

An Introduction to Hornworts

Anthoceros sp. Photo by Bramadi Arya licensed under CC BY-SA 4.0

When was the last time you thought about hornworts? Have you ever thought about hornworts? If you answered no, you aren’t alone. Despite their global distribution, these tiny plants receive hardly any attention and that is a shame. Hornworts (Anthocerotophyta) have been around for a very long time. In fact, it is likely that they were some of the first plants to colonize the land roughly 300 - 400 million years ago.

To be fair, hornworts aren’t known for their size. They are generally small plants, though their colonies can form impressive mats. To find them, one must try looking in and among rocks, bare patches of soil, or pretty much anywhere enough moisture builds up to supply their needs. They tend to enjoy nutrient-poor substrates but I would hesitate to say that with any certainty. No matter where you live, from the tundra to the tropics, there is probably a hornwort native to your neck of the woods.

Dendroceros sp. Photo by J.Ziffer licensed under public domain

How many different species of hornwort there are is apparently the subject of some debate. Some authors recognize upwards of 300 species whereas others suggest the real number hangs somewhere around 150. Regardless of the exact numbers, hornworts belong to one of six genera: Anthoceros, Dendroceros, Folioceros, Megaceros, Notothylas and Phaeoceros. Fun fact, the suffix ‘ceros’ at the end of each genus is derived from the Latin word for ‘horn.’

The reason they are called hornworts is because of their reproductive structures or “sporophytes.” Similar to their moss and liverwort cousins, hornworts undergo an alternation of generations in order to reproduce sexually. The green gametophytes house the sexual organs - antheridia if they are male and archegonia if they are female. After fertilization, a sporophyte begins to grow, which will go on to produce and disseminate spores. However, the way in which the hornwort sporophyte forms is a bit different from what we see in mosses and liverworts.

Alternation of generations in hornworts. Photo by Mariana Ruiz (LadyofHats) licensed under public domain

Upon fertilization, the zygote begins to divide into a bulbous mass of cells affectionately referred to as "the foot.” This foot remains within the gametophyte throughout the lifetime of the hornwort, depending on the gametophyte for water and nutrients. Even more peculiar is the the fact that the growing point of the sporophyte is at the base rather than the tip. As such, the horn of each hornwort could continue to grow upwards until it is damaged in some way.

The horn itself is an amazing structure. Whereas the outside layers of tissue are merely structural, the internal tissues differentiate into two different types - spores and pseudo-elaters. Pseudo-elaters expand and contract as humidity fluctuates so as the sporophyte splits to release the spores, the pseudo-elaters dehydrate and snap like tiny spore catapults, thus aiding in their dispersal.

Megaceros flagellaris. Photo by Dr. Scott Zona licensed under CC BY-NC 2.0

Of course, reproduction is the main goal but to get to that point, hornworts must grow and mature. How they manage to survive is incredible because it is a reminder that what are often thought of as “primitive” plants are actually far more advanced than we give them credit for. The main body of the hornwort gametophyte is a thin layer of cells that spread out to form a tiny, green mat. This is the structure you are most likely to encounter.

Inside each cell is a single chloroplast. In most hornworts, the chloroplast does not exist in isolation. Instead, it is fused with other organelles into a structure called a “pyrenoid.” The pyrenoid functions as both a center for photosynthesis and a food storage organ. This is unique as it relates to terrestrial plants but quite common in algae. Another odd fact about hornwort anatomy are the presence of tiny cavities scattered throughout their tissues. These cavities form as clusters of hornwort cells die. They then fill with a special mucilage that appears to invite colonization by nitrogen-fixing cyanobacteria. The cyanobacteria set up shop within the cavities and provides the hornwort with supplemental nitrogen in return for a place to live.

Anthoceros agrestis photo by BerndH licensed under CC BY-SA 3.0

Cyanobacteria aren’t the only organisms to have partnered with hornworts either. Mycorrhizal fungi also enter into the picture. A study done back in 2013 actually found that a wide variety of fungi will partner with hornworts which suggests that this symbiotic relationship is much more ancient and versatile than we once thought. Fungi cluster around parts of the gametophyte that produce root-like structures called “rhizoids,” offering nutrients in return for carbohydrates.

All in all, I think it is safe to say that hornworts are remarkable little plants. Though they can sometimes be difficult to find and properly identify, they nonetheless offer plenty of inspiration for the botanically inclined mind. We can all do better by tiny plants like the hornworts. They have been on land for an incredible amount of time and they definitely deserve our respect and admiration.

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

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

Meet the Fire Lily

Photo by Callan Cohen licensed under CC BY-SA 3.0

The flora of the South African fynbos region is no stranger to fire. Many species have adapted to cope with and even rely on fire to complete their lifecycles. There is one species, however, that takes this to the extreme. It is a tiny member of the Amaryllidaceae aptly named the fire lily (Cyrtanthus ventricosus).

The fire lily is not a big plant by any means. Mature individuals can top out around 9 inches (250 mm) and for most of the year consist of a nothing more than a small cluster of narrow, linear leaves. As the dry months of summer approach, the leaves senesce and the plant more or less disappears until its time to flower. However, unlike other plants in this region that flower more regularly, the fire lily lies in wait for a very specific flowering cue - smoke.

It has been noted that fire lilies only seem to want to reproduce after a fire. No other environmental factor seems to trigger flowering. This has made them quite frustrating for bulb aficionados. Only after a fire burns over the landscape will a scape emerge topped with anywhere from 1 to 12 tubular red flowers.

This dependence on fire for flowering has garnered the attention of a few botanists concerned with conservation of pyrophytic geophytes. Obviously if we care about conserving species like the fire lily, it is extremely important that we understand their reproductive ecology. The question of fire lily blooming is one of triggers. What part of the burning process triggers these plants to bloom?

By experimenting with various burn and smoke treatments, researchers were able to deduce that it wasn’t heat that triggered flowering but rather something in the smoke itself. Though researchers were not able to isolate the exact chemical(s) responsible, at least we now know that fire lilies can be coaxed into flowering using smoke alone. This is a real boon to growers and conservationists alike.

Photo by Callan Cohen licensed under CC BY-SA 3.0

Seeing a population of fire lilies in full bloom must be an incredible sight. Within only a few days of a fire, huge patches of bright red flowers decorate the charred landscape. They are borne on hollow stalks which provide lots of structural integrity while being cheap to produce. The flowers themselves are not scented but they do produce a fair amount of nectar. The bright red inflorescence mainly attracts the Table Mountain pride butterfly as well as sunbirds.

Once flowering is complete, seeds are produced and the plants return to their dormant bulbous state until winter when leaves emerge again. Flowering will not happen again until fire returns to clear the landscape. This strategy may seem inefficient on the part of the plant. Why not attempt to reproduce every year? The answer is competition. By waiting for fire, this tiny plant is able to make a big impact despite being so small. It would be impossible to miss their enticing floral display when all other vegetation has been burned away.

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

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

Meet the Pygmy Clubmoss

Photo by Leon Perrie licensed under CC BY 4.0

No, these are not some sort of grass or rush. What you are looking at here is actually a member of the clubmoss family (Lycopodiaceae). Colloquially known as the pygmy clubmoss, this odd little plant is the only species in its genus - Phylloglossum drummondii. Despite its peculiar nature, very little is known about it.

The pygmy clubmoss is native to parts of Australia, Tasmania, and New Zealand but common it is not. From what I can gather, it grows in scattered coastal and lowland sites where regular fires clear the ground of competing vegetation. It is a perennial plant that makes its appearance around July and reaches reproductive size around August through to October.

Reproduction for the pygmy clubmoss is what you would expect from this family. In dividual plants will produce a reproductive stem that is tipped with a cone-like structure. This cone houses the spores, which are dispersed by wind. If a spore lands in a suitable spot, it germinates into a tiny gametophyte. As you can probably imagine, the gametophyte is small and hard to locate. Indeed, little is known about this part of its life cycle. Nonetheless, like all gametophytes, the end goal of this stage is sexual reproduction. Sperm are released and with any luck will find a female gametophyte and fertilize the ovules within. From the fertilized ovule emerges the sporophytes we see pictured above.

As dormancy approaches, this strange clubmoss retreats underground where it persists as a tiny tuber-like stem. Though it is rather obscure no matter who you ask, there has been some scientific attention paid to this odd little plant, especially as it relates to its position on the tree of life. Since it was first described, its taxonomic affinity has moved around a bit. Early debates seemed to center around whether it belonged in Lycopodiaceae or its own family, Phylloglossaceae.

Recent molecular work put this to rest showing that genetically the pygmy clubmoss is most closely related to another genus of clubmoss - Huperzia. This was bolstered by the fact that it shares a lot of features with this group such as spore morphology, phytochemistry, and chromosome number. The biggest difference between these two genera is the development of the pygmy clubmoss tuber, which is unique to this species. However, even this seems to have its roots in Lycopodiaceae.

If you look closely at the development of some lycopods, it becomes apparent that the pygmy clubmoss most closely resembles an early stage of development called the “protocorm.” Protocorms are a tuberous mass of cells that is the embryonic form of clubmosses (as well as orchids). Essentially, the pygmy clubmoss is so similar to the protocorm of some lycopods that some experts actually think of it as a permanent protocorm capable of sexual reproduction. Quite amazing if you ask me.

Sadly, because of its obscurity, many feel this plant may be approaching endangered status. There have been notable declines in population size throughout its range thanks to things like conversion of its habitat to farmland, over-collection for both novelty and scientific purposes, and sequestration of life-giving fires. As mentioned, the pygmy clubmoss needs fire. Without it, natural vegetative succession quickly crowds out these delicate little plants. Hopefully more attention coupled with better land management can save this odd clubmoss from going the way of its Carboniferous relatives.

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

Gymnosperms and Fleshy "Fruits"

Fleshy red aril surrounding the seeds of Taxus baccata. Photo by Frank Vincentz licensed under the GNU Free Documentation License.

Many of us were taught in school that one of the key distinguishing features between gymnosperms and angiosperms is the production of fruit. Fruit, by definition, is a structure formed from the ovary of a flowering plant. Gymnosperms, on the other hand, do not enclose their ovules in ovaries. Instead, their unfertilized ovules are exposed (to one degree or another) to the environment. The word “gymnosperm” reflects this as it is Greek for “naked seed.” However, as is the case with all things biological, there are exceptions to nearly every rule. There are gymnosperms on this planet that produce structures that function quite similar to fruits.

Internal anatomy of a Ginkgo ovule with red arrow showing the integument.

Photo copyright Bruce Kirchoff, Licensed under CC BY 2.0

The key to understanding this evolutionary convergence lies in understanding the benefits of fruits in the first place. Fruits are all about packing seeds into structures that appeal to the palates of various types of animals who then eat said fruits. Once consumed, the animals digest the fruity bits and will often deposit the seeds elsewhere in their feces. Propagule dispersal is key to the success of plants as it allows them to not only to complete their reproductive cycle but also conquer new territory in the process. With a basic introduction out of the way, let’s get back to gymnosperms.

“Fruits” of Cephalotaxus fortunei (Cephalotaxaceae)

There are 4 major gymnosperm lineages on this planet - the Ginkgo, cycads, gnetophytes, and conifers. Each one of these groups contains members that produce fleshy structures around their seeds. However, their “fruits” do not all develop in the same way. The most remarkable thing to me is that, from a developmental standpoint, each lineage has evolved its own pathway for “fruit” production.

Ginkgo “fruits” are full of butyric acid and smell like rotting butter or vomit. Photo by H. Zell licensed under CC BY-SA 3.0

For instance, consider ginkgos and cycads. Both of these groups can trace their evolutionary history back to the early Permian, some 270 - 280 million years ago, long before flowering plants came onto the scene. Both surround their developing seed with a layer of protective tissue called the integument. As the seed develops, the integument swells and becomes quite fleshy. In the case of Ginkgo, the integument is rich in a compound called butyric acid, which give them their characteristic rotten butter smell. No one can say for sure who this nasty odor originally evolved to attract but it likely has something to do with seed dispersal. Modern day carnivores seem to be especially fond of Ginkgo “fruits,” which would suggest that some bygone carnivore may have been the main seed disperser for these trees.

“Fruits” contained within the female cone of a cycad (Lepidozamia peroffskyana). Photo by Tony Rodd licensed under CC BY-NC-SA 2.0

The Gnetophytes are represented by three extant lineages (Gnetaceae, Welwitschiaceae, and Ephedraceae), but only two of them - Gnetaceae and Ephedraceae - produce fruit-like structures. As if the overall appearance of the various Gnetum species didn’t make you question your assumptions of what a gymnosperm should look like, its seeds certainly will. They are downright berry-like!

Berry-like seeds of Gnetum gnemon. Photo by gbohne licensed under CC BY-SA 2.0

The formation of the fruit-like structure surrounding each seed can be traced back to tiny bracts at the base of the ovule. After fertilization, these bracts grow up and around the seed and swell to become red and fleshy. As you can imagine, Gnetum “fruits” are a real hit with animals. In the case of some Ephedra, the “fruit” is also derived from much larger bracts that surround the ovule. These bracts are more leaf-like at the start than those of their Gnetum cousins but their development and function is much the same.

Red, fleshy bracts of Ephedra distachya. Photo by Le.Loup.Gris licensed under CC BY-SA 3.0

Whereas we usually think of woody cones when we think of conifers, there are many species within this lineage that also have converged on fleshy structures surrounding their seeds. Probably the most famous and widely recognized example of this can be seen in the yews (Taxus spp.). Ovules are presented singly and each is subtended by a small stalk called a peduncle. Once fertilized, a group of cells on the peduncle begin to grow and differentiate. They gradually swell and engulf the seed, forming a bright red, fleshy structure called an “aril.” Arils are magnificent seed dispersal devices as birds absolutely relish them. The seed within is quite toxic so it usually escapes the process unharmed and with any luck is deposited far away from the parent plant.

The berry-like cones of Juniperus communis. Photo by Piero Amorati, ICCroce - Casalecchio di Reno, Bugwood.org licensed under Creative Commons Attribution 3.0 License.

Another great example of fleshy conifer “fruits” can be seen in the junipers (Juniperus spp.). Unlike the other gymnosperms mentioned here, the junipers do produce cones. However, unlike pine cones, the scales of juniper cones do not open to release the seeds inside. Instead, they swell shut and each scale becomes quite fleshy. Juniper cones aren’t red like we have seen in other lineages but they certainly garnish the attention of many a small animal looking for food.

I have only begun to scratch the surface of the fruit-like structures in gymnosperms. There is plenty of literary fodder out there for those of you who love to read about developmental biology and evolution. It is a fascinating world to uncover. More importantly, I think the fleshy “fruits” of the various gymnosperm lineages stand as a testament to the power of natural selection as a driving force for evolution on our planet. It is amazing that such distantly related plants have converged on similar seed dispersal mechanisms by so many different means.

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

Further Reading: [1] [2] [3] [4] [5] [6] [7]

Arctic Vegetation is Growing Taller & Why That Matters

The Arctic ecosystem is changing and it is doing so at an alarming rate. Indeed, the Arctic Circle is warming faster than most other ecosystems on this planet. All of this change has implications for the plant communities that call this region home. In a landmark study that incorporated thousands of data points from places like Alaska, Canada, Iceland, Scandinavia, and Russia, researchers have demonstrated that Arctic vegetation is, on average, getting taller.

Imagine what it is like to be a plant growing in the Arctic. Extreme winds, low temperatures, a short growing season, and plenty of snow are just some of the hardships that characterize life on the tundra. Such harsh conditions have shaped the plants of this region into what we know and love today. Arctic plants tend to hug the ground, hunkering down behind whatever nook or cranny offers the most respite from their surroundings. As such, plants of Arctic-type habitats tend to be pretty small in stature. As you can probably imagine, if these limits to plant growth become less severe, plants will respond accordingly.

That is part of what makes this new paper so alarming. The vegetation that comprise these Arctic communities is nearly twice as tall today as it was 30 years ago. However, the increase in height is not because the plants that currently grow there are getting taller but rather because new plants are moving northwards into these Arctic regions. New players in the system are usually cause for concern. Other studies have shown that it isn’t warming necessarily that hurts Arctic and alpine plants but rather competition. They simply cannot compete as well with more aggressive plant species from lower latitudes.

Taller plants moving into the Arctic may have even larger consequences than just changes in species interactions. It can also change ecosystem processes, however, this is much harder to predict. One possible consequence of taller plants invading the Arctic involves carbon storage. It is possible that as conditions continue to favor taller and more woody vegetation, there could actually be more carbon storage in this system. Woody tissues tend to sequester more carbon and shading from taller vegetation may slow decomposition rates of debris in and around the soil.

It is also possible that taller vegetation will alter snowpack, which is vital to the health and function of life in the Arctic. Taller plants with more leaf area could result in a reduced albedo in the surrounding area. Lowering the albedo means increased soil temperatures and reduced snowpack as a result. Alternatively, taller plants could also increase the amount of snowpack thanks to snow piling up among branches and leaves. This could very well lead (counterintuitively) to warmer soils and higher decomposition rates as snowpack acts like an insulating blanket, keeping the soil slightly above freezing throughout most of the winter.

It is difficult to make predictions on how a system is going to respond to massive changes in the average conditions. However, studies looking at how vegetation communities are responding to changes in their environment offer us one of the best windows we have into how ecosystems might change moving into the uncertain future we are creating for ourselves.

Photo Credits: [2]

Further Reading: [1]

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]

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]

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?

Big Things Come In Small Packages

Meet Blossfeldia liliputana, the smallest species of cactus in the world. With a maximum diameter of only 12 mm, this wonderful succulent would be hard to spot tucked in among the nooks and crannies of rock outcrops. Its species name "liliputana" is a reference to the fictional island of Liliput (Gulliver's Travels) whose inhabitants were said to be rather small. If its size alone wasn't interesting in and of itself, the biology of B. liliputana is also downright bizarre.

Blossfeldia liliputana is native to arid regions between southern Bolivia and northern Argentina. It appears to prefer growing wedged between cracks in rock as these are usually the spots where just enough soil builds up to put down its roots. Root formation, however, does not happen for quite some time. Most often new individuals bud off from the parent plant. They emerge not from the base, but rather from apical tissues, yet another unique feature of this cactus. What's more, this cactus produces no spines. Instead, its numerous areoles are covered in a dense layer of trichomes that are felt-like to the touch.

As you can clearly see, this species is small. It only ever becomes conspicuous when it comes time to flower. Imagine a bunch of tiny white to pink cactus flowers poking out of a crevice. It must be a remarkable sight to see in person. Despite their showy appearance, its is believed that most are self-fertilized.

Photo by Mats Winberg licensed under CC BY-SA 2.5

As mentioned, the size of this cactus isn't the only interesting thing about its biology. B. liliputana is categorized as a poikilohydric organism, meaning it doesn't have the ability to regulate its internal water content. Researchers have found that individual plants can lose up to 80% of their weight in water and can maintain that state for as long as two years without any negative effects. As such, colonies of these tiny cacti often appear shrunken or squished. Once the rains arrive, however, it springs back to its original rounded shape with seemingly no issues. Amazingly, a significant amount of water uptake happens via the fuzzy areoles that cover its surface, hence it does not harm the plant to hold off growing roots for quite some time. 

Photo by AstroKaktus at Slovenian Wikipedia licensed under the GNU Free Documentation License

Speaking of water regulation, B. liliputana holds another record for having the lowest density of stomata of any terrestrial autotrophic vascular plant. Stomata are the pores in which plants regulate water and gas exchange so having so few may have something to do with why this species loses and gains water to such a degree that would kill most other vascular plant species.

Another peculiar quality of this cactus are its seeds. Unlike all other cacti whose seeds are hard and relatively smooth, the seeds of B. liliputana are hairy. Attached to each seed is a small fleshy structure called an aril, which aids in seed dispersal. As it turns out, B. liliputana relies on ants as its main seed dispersers. Ants attracted to the fleshy aril drag the seeds back to their nests, remove and eat the aril, and then discard the seed. This is often good news for the cactus because its seeds end up in nutrient-rich ant middens protected from both the elements and seed predators, often in much more suitable conditions for germination.

Photo by Michael Wolf licensed under CC BY-SA 3.0

Needless to say, B. liliputana is a bit of an oddball as far as cacti are concerned. Its highly derived features coupled with its bizarre biology have made it difficult for taxonomists to elucidate its relationship to the rest of the cactus family. It certainly deserves its own genus, to which it is the only member, however, it has been added to and removed form a handful of cactus subfamilies over the years. The most recent genetic analyses suggests that it is unique enough to warrant its own tribe within Cactaceae - Blossfeldieae.

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

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

How Aroids Turn Up the Heat

Photo by Jörg Hempel licensed under CC BY-SA 2.0

A subset of plants have evolved the ability to produce heat, a fact that may come as a surprise to many reading this. The undisputed champions of botanical thermogenesis are the aroids (Araceae). Exactly why they do so is still the subject of scientific debate but the means by which heat is produced is absolutely fascinating.

The heat producing organ of an aroid is called the spadix. Technically speaking, a spadix is a spike of minute flowers closely arranged around a fleshy axis. All aroid inflorescences have one and they come in a wide variety of shapes, colors, and textures. To produce heat, the spadix is hooked up to a massive underground energy reserve largely in the form of carbohydrates or sugars. The process of turning these sugars into heat is rather complex and surprisingly animal-like.

Cross section of a typical aroid inflorescence with half of the protective spathe removed. The spadix is situated in the middle with a rings of protective hairs (top), male flowers (middle), and female flowers (bottom). Photo by Kristian Peters -- Fabelfroh licensed under CC BY-SA 3.0

It all starts with a compound we are rather familiar with - salicylic acid - as it is the main ingredient in Aspirin. In aroids, however, salicylic acid acts as a hormone whose job it is to initiate both the heating process as well as the production of floral scents. It signals the mitochondria packed inside a ring of sterile flowers located at the base of the spadix to change their metabolic pathway.

In lieu of their normal metabolic pathway, which ends in the production of ATP, the mitochondria switch over to a pathway called the "Alternative Oxidase Metabolic Pathway." When this happens, the mitochondria start burning sugars using oxygen as a fuel source. This form of respiration produces heat.

Thermal imaging of the inflorescence of Arum maculatum.

As you can imagine, this can be a costly process for plants to undergo. A lot of energy is consumed as the inflorescence heats up. Nonetheless, some aroids can maintain this costly level of respiration intermittently for weeks on end. Take the charismatic skunk cabbage (Symplocarpus foetidus) for example. Its spadix can reach temperatures of upwards of 45 °F (7 °C) on and and off for as long as two weeks. Even more incredible, the plant is able to do this despite freezing ambient temperatures, literally melting its way through layers of snow.

For some aroids, however, carbohydrates just don't cut it. Species like the Brazilian Philodendron bipinnatifidum produce a staggering amount of floral heat and to do so requires a different fuel source - fat. Fats are not a common component of plant metabolisms. Plants simply have less energy requirements than most animals. Still, this wonderful aroid has converged on a fat-burning metabolic pathway that puts many animals to shame. 

The inflorescence of Philodendron bipinnatifidum can reach temps as high as 115 °F (46 °C). Photo by Tekwani licensed under CC BY-SA 3.0

P. bipinnatifidum stores lots of fat in sterile male flowers that are situated between the fertile male and female flowers near the base of the spadix. As soon as the protective spathe opens, the spadix bursts into metabolic action. As the sun starts to set and P. bipinnatifidum's scarab beetle pollinators begin to wake up, heat production starts to hit a crescendo. For about 20 to 40 minutes, the inflorescence of P. bipinnatifidum reaches temperatures as high as 95 °F (35 °C) with one record breaker maxing out at 115 °F (46 °C)! Amazingly, this process is repeated again the following night.

It goes without saying that burning fat at a rate fast enough to reach such temperatures requires a lot of oxygen. Amazingly, for the two nights it is in bloom, the P. bipinnatifidum inflorescence consumes oxygen at a rate comparable to that of a flying hummingbird, which are some of the most metabolically active animals on Earth.

The world's largest inflorescence belongs to the titan arum (Amorphophallus titanum) and it too produces heat. Photo by Fbianh licensed under CC0 1.0

Again, why these plants go through the effort of heating their reproductive structures is still a bit of a mystery. For most, heat likely plays a role in helping to volatilize floral scents. Anyone that has spent time around blooming aroids knows that this plant family produces a wide range of odors from sweet and spicy to downright offensive. By warming these compounds, the plant may be helping to lure in pollinators from a greater distance away. It is also thought that the heat may be an attractant in and of itself. This is especially true for temperate species like the aforementioned skunk cabbage, which frequently bloom during colder months of the year. Likely both play a role to one degree or another throughout the aroid family.

What we can say is that the process of plant thermogenesis is absolutely fascinating and well worth deeper investigation. We still have much to learn about this charismatic group of plants.

LEARN MORE ABOUT AROID POLLINATION HERE



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

Further Reading: [1] [2] [3] [4] [5] [6] [7] [8]

Of Bluebells and Fungi

Photo by Christophe Couckuyt licensed under CC BY 2.0

Whether in your garden or in the woods, common bluebells (Hyacinthoides non-scripta) are a delightful respite from the dreary months of winter. It should come as no surprise that these spring geophytes are a staple in temperate gardens the world over. And, as amazing as they are in the garden, bluebells are downright fascinating in the wild.

Bluebells can be found growing naturally from the northwestern corner of Spain north into the British Isles. They are largely a woodland species, though finding them in meadows isn't uncommon. They are especially common in sites that have not experienced much soil disturbance. In fact, large bluebell populations are used as indicators of ancient wood lots.

Photo by RX-Guru licensed under CC BY-SA 3.0

Being geophytes, bluebells cram growth and reproduction into a few short weeks in spring. We tend to think of plants like this as denizens of shade, however, most geophytes get going long before the canopy trees have leafed out. As such, these plants are more accurately sun bathers. On warm days, various bees can be seen visiting the pendulous flowers, with the champion pollinator being the humble bumble bees.

The above ground beauty of bluebells tends to distract us from learning much about their ecology. That hasn't stopped determined scientists though. Plenty of work has been done looking at how bluebells make their living and get on with their botanical neighbors. In fact, research is turning up some incredible data regarding bluebells and mycorrhizal fungi.

Photo by Mick Garratt licensed under CC BY-SA 2.0

Bluebell seeds tend not to travel very far, most often germinating near the base of the parent. Germination occurs in the fall when temperatures begin to drop and the rains pick up. Interestingly, bluebell seeds actually germinate within the leaf litter and begin putting down their initial root before the first frosts. Often this root is contractile, pulling the tiny seedling down into the soil where it is less likely to freeze. During their first year, phosphorus levels are high. Not only does the nutrient-rich endosperm supply the seedling with much of its initial needs, abundant phosphorus near the soil surface supplies more than enough for young plants. This changes as the plants age and change their position within the soil.

Photo by MichaelMaggs licensed under CC BY-SA 3.0

Over the next 4 to 5 years, the bluebell's contractile roots pull it deeper down into the soil, taking it out of the reach of predators and frost. This also takes them farther away from the nutrient-rich surface layers. What's more, the roots of older bluebells are rather simple structures. They do not branch much, if at all, and they certainly do not have enough surface area for proper nutrient uptake. This is where mycorrhizae come in.

Bluebells partner with a group of fungi called arbuscular mycorrhiza, which penetrate the root cells, thus greatly expanding the effective rooting zone of the plant. Plants pay these fungi in carbohydrates produced during photosynthesis and in return, the fungi provide the plants with access to far more nutrients than they would be able to get without them. One of the main nutrients plants gain from these symbiotic fungi is phosphorus.

Photo by Oast House Archive licensed under CC BY-SA 2.0

For bluebells, with age comes new habitat, and with new habitat comes an increased need for nutrients. This is why bluebells become more dependent on arbuscular mycorrhiza as they age. In fact, plants grown without these fungi do not come close to breaking even on the nutrients needed for growth and maintenance and thus live a shortened life of diminishing returns. This is an opposite pattern from what we tend to expect out of mycorrhizal-dependent plants. Normally its the seedlings that cannot live without mycorrhizal symbionts. It just goes to show you that even familiar species like the bluebell can offer us novel insights into the myriad ways in which plants eke out a living.

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

Further Reading: [1] [2]

One Mustard, Many Flavors

Photo by Kurt Kulac licensed under CC BY-SA 3.0

What do kale, broccoli, cauliflower, Brussel sprouts, and cabbage have in common? They are all different cultivars of the same species!

Wild cabbage (Brassica oleracea) is native to coastal parts of southern and western Europe. In its native habitat, wild cabbage is very tolerant of salty, limey soils but not so tolerant of competition. Because of this, it tends to grow mainly on limestone sea cliffs where few other plants can dig their roots in.

Despite their popularity as delicious, healthy vegetables, as well as their long history of cultivation, there is scant record of this plant before Greek and Roman times. Some feel that this is one of the oldest plants in cultivation. Along with the countless number of edible cultivars, the wild form of Brassica oleracea can be found growing throughout the world, no doubt thanks to its popularity among humans.

I am always amazed by how little we know about crop wild relatives. Despite the popularity of its many agricultural cultivars, relatively little attention has been paid to B. oleracea in the wild. What we do know is that at least two subspecies have been identified - B. oleracea ssp. bourgeaui and B. oleracea L. ssp. oleracea. As far as anyone can tell, subspecies 'oleracea' is the most wide spread in its distribution whereas subspecies 'bourgeaui'  is only known from the Canary Islands. 

© Copyright Evelyn Simak licensed under CC BY-SA 2.0

B. oleracea's long history with humans confuses matters quite a bit. Because it has been cultivated for thousands of years, identifying which populations represent wild individuals and which represent ancient introductions is exceedingly difficult. Such investigations are made all the more difficult by a lack of funding for the kind of research that would be needed to elucidate some of these mysteries. We know so little about wild B. oleracea that the IUCN considers is a species to be "data deficient."

It seems to appreciate cool, moist areas and will sometimes escape from cultivation if conditions are right, thus leading to the confusion mentioned above. It is amazing to look at this plant and ponder all the ways in which humans have selectively bred it into the myriad shapes, sizes, and flavors we know and love (or hate) today! However, we must pay more attention to the wild progenitors of our favorite crops. They harbor much needed genetic diversity as well as clues to how these plants are going to fare as our climates continue to change.

Photo Credit: [1] [2]

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

North America's Pachysandra

Photo by Salicyna licensed under CC BY-SA 4.0

In the interest of full disclosure, I have never been a fan of garden variety Pachysandra. Long before I had any interest in plants or gardening, there was something about this groundcover that simply did not appeal to me. Fast forward more than a decade and my views on the use of Asian Pachysandra in the garden have not changed much. You can imagine my surprise then when I learned that North America has its own representative of this genus - the Allegheny spurge (Pachysandra procumbens).

My introduction to P. procumbens happened during a tour of the Highlands Botanical Garden in Highlands, North Carolina. I recognized its shape and my initial reaction was alarm that a garden specializing in native plants would showcase a non-native species. My worry was quickly put to rest as the sign informed me that this lovely groundcover was in fact indigenous to this region. Indeed, P. procumbens can be found growing in shady forest soils from North Carolina down to Florida and Texas.

Photo by David J. Stang licensed under CC BY-SA 4.0

This species is yet another representative of a curious disjunction in major plant lineages between North America and eastern Asia. Whereas North America has this single species of Pachysandra, eastern Asia boasts two, P. axillaris and P. terminalis. Such a large gap in the distribution of this genus (as well as many others) seems a bit strange until one considered the biogeographic history of the two continents.

Many thousands of years ago, sea levels were much lower than they are today. This exposed land bridges between continents which today are hundreds of feet under water. During favorable climatic periods, Asia and North America likely shared a considerable amount of their respective floras, a fact we still find evidence of today. The Pachysandra are but one example of a once connected distribution that has been fragmented by subsequent sea level rise. Fossil records of Pachysandra have been found in regions of British Columbia, Washington, Oregon, Wyoming, and North and South Dakota and provide further confirmation of this.

As a species, P. procumbens is considered a subshrub. It is slow growing but given time, populations can grow to impressive sizes. In spring, numerous fragrant, white flower spikes emerge that are slowly eclipsed by the flush of spring leaf growth. The flowers themselves are intriguing structures worthy of close inspection. Their robust form is what gives this genus its name. "Pachys" is Greek for thick and "andros" is Greek for male, which refers to the thickened filaments that support the anthers.

It is hard to say for sure why this species is not as popular in horticulture as its Asian cousins. It tolerates a wide variety of soil types and does well in shade. What's more, it is mostly ignored by all but the hungriest of deer. And, at the end of the day, it took this species to change my mind about Pachysandra. After all, each and every species has a story to tell.

Photo Credits: [1] [2]

Further Reading: [1] [2]

Apocynaceae Ant House

Bullate leaves help the vine clasp to the tree as well as house ant colonies. Photo by Richard Parker licensed under CC BY-NC-SA 2.0

The dogbane family, Apocynaceae, comes in many shapes, sizes, and lifestyles. From the open-field milkweeds we are most familiar with here in North America to the cactus-like Stapeliads of South Africa, it would seem that there is no end to the adaptive abilities of this family. Being an avid gardener both indoors and out, the diversity of Apocynaceae means that I can be surrounded by these plants year round. My endless quest to grow new and interesting houseplants was how I first came to know a genus within the family that I find quite fascinating. Today I would like to briefly introduce you to the Dischidia vines.

The genus Dischidia is native to tropical regions of China. Like its sister genus Hoya, these plants grow as epiphytic vines throughout the canopy of warm, humid forests. Though they are known quite well among those who enjoy collecting horticultural curiosities, Dischidia as a whole is relatively understudied. These odd vines do not attach themselves to trees via spines, adhesive pads, or tendrils. Instead, they utilize their imbricated leaves to grasp the bark of the trunks and branches they live upon.

The odd, bulb-like leaves of the urn vine (Dischidia rafflesiana) Photo by Bernard DUPONT licensed under CC BY-SA 2.0

One thing we do know about this genus is that most species specialize in growing out of arboreal ant nests. Ant gardens, as they are referred to, offer a nutrient rich substrate for a variety of epiphytic plants around the world. What's more, the ants will visciously defend their nests and thus any plants growing within.

The flowers of Dischidia ovata Photo by Krzysztof Ziarnek, Kenraiz licensed under CC BY-SA 4.0

Some species of Dischidia take this relationship with ants to another level. A handful of species including D. rafflesiana, D. complex, D. major, and D. vidalii produce what are called "bullate leaves." These leaves start out like any other leaf but after a while the edges stop growing. This causes the middle of the leaf to swell up like a blister. The edges then curl over and form a hollow chamber with a small entrance hole.

Photo by Krzysztof Ziarnek, Kenraiz licensed under CC BY-SA 4.0

These leaves are ant domatia and ant colonies quickly set up shop within the chambers. This provides ample defense for the plant but the relationship goes a little deeper. The plants produce a series of roots that crisscross the inside of the leaf chamber. As ant detritus builds up inside, the roots begin to extract nutrients. This is highly beneficial for an epiphytic plant as nutrients are often in short supply up in the canopy. In effect, the ants are paying rent in return for a place to live.

Growing these plants can take some time but the payoff is worth. They are fascinating to observe and certainly offer quite a conversation piece as guests marvel at their strange form.

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

Further Reading: [1]

The Giant Genomes of Geophytes

Canopy plant (Paris japonica) Photo by Radek Szuban licensed under CC BY-NC 2.0

A geophyte is any plant with a short, seasonal lifestyle and some form of underground storage organ ( bulb, tuber, thick rhizome, etc.). Plants hailing from a variety of families fall into this category. However, they share more than just a similar life history. A disproportionate amount of geophytic plants also possess massive genomes. 

As we have discussed in previous posts, life isn't easy for geophytes. Cold temperatures, a short growing season, and plenty of hungry herbivores represent countless hurdles that must be overcome. That is why many geophytes opt for rapid growth as soon as conditions are right. However, they don't do this via rapid cell division. 

Dutchman's breeches (Dicentra cucullaria) emerging with preformed buds.

Instead, geophytes spend the "dormant" months pre-growing all of their organs. What's more, the cells that make up their leaves and flowers are generally much larger than cells found in non-geophytes. This is where that large genome comes into plant. If they had to wait until the first few weeks of spring to start their development, a large genome would only get in the way. Their dormant season growth means that these plants don't have to worry about streamlining the process of cellular division. They can take their time. 

As such, an accumulation of genetic material isn't detrimental. Instead, it may actually be quite beneficial for geophytes. Associated with large genomes are things like larger stomata, which helps these plants better regulate their water needs. The large genomes may very well be the reason that many geophytic plants are so good at taking advantage of such ephemeral growing conditions. 

When the right conditions present themselves, geophytes don't waste time. Pre-formed organs like leaves and flowers simply have to fill with water instead of having to wait for tissues to divide and differentiate. Water is plentiful during the spring so geophytes can rely on turgor pressure within their large cells for stability rather than investing in thick cell walls. That is why so many spring blooming plants feel so fleshy to the touch. 

Taken together, we can see how large genomes and a unique growth strategy have allowed these plants to exploit seasonally available habitats. It is worth noting, however, that this is far from the complete picture. With such a wide variety of plant species adopting a geophytic lifestyle, we still have a lot to learn about the secret lives of these plants.

Photo Credits: [1] [2]

Further Reading: [1]