The First Genus (Alphabetically)

Photo by Eric in SF licensed under CC BY-SA 3.0

One thing I love about orchids is that they are so diverse. One could spend their entire life studying these plants and never run out of surprises. Every time I sit down with an orchid topic in mind, I end up going down a rabbit hole of immeasurable depth. I love this because I always end up learning new and interesting facts. For instance, I only recently learned that there is a genus of orchids that has been given the unbelievably complex name of Aa.

No, that is not an abbreviation. The genus was literally named Aa. As far as I have been able to tell, it is pronounced “ah” rather than “ay,” but if any linguists are reading this and beg to differ, please chime in! Regardless, I was floored by this silly exercise in plant naming and had to learn more. I had never heard of this genus before and figured that it was so obscure that it probably contained, at most, only a small handful of species. This assumption was wrong.

Aa maderoi. Photo by Dr. Alexey Yakovlev licensed under CC BY-SA 2.0

Though by no means massive, the genus Aa contains at least 25 recognized species. A quick search of the literature even turned up a few relatively recent papers describing new species. Apparently we have a ways to go in understanding their diversity. Nonetheless, this is an interesting and pretty genus of orchids.

From what I gather, Aa are most often found growing at high elevations in the Andes, though at least one species is native to mountainous areas of Costa Rica. They are terrestrial orchids that prefer cooler temperatures and fairly moist soil. Some species are said to only be found in close proximity to mountain streams. Some of the defining features of the genus are a tall inflorescence jam packed with tiny inconspicuous, greenish-white flowers. The flowers are surrounded by semi-transparent sheaths that are surprisingly showy. All in all, they kind of remind me of a mix between Spiranthes and Goodyera.

Close up of an inflorescence of Aa maderoi showing the small, white flowers and large, semi-transparent sheaths. Photo by Dr. Alexey Yakovlev licensed under CC BY-SA 2.0

But what about the name? Why in the world was this genus given such a strange and abrupt moniker? The answer seems to be the silliest option I could think of: to be first. This genus was originally described in 1845 by German botanist Heinrich Gustav Reichenbach who recognized two species within the genus Altensteinia to be distinct enough to warrant their own genus.

According to most sources I could find, he coined this new genus Aa so that it would appear first on all taxonomic lists. There is at least one other report that the name was given in honor of a man by the name of Pieter van der Aa, but apparently this is “highly” disputed. However, all of this should be taken with a grain of salt. Though I can find plenty of literature describing various species within the genus, I could turn up no actual literature on the naming of the genus itself. All I could find is what has been repeated (almost verbatim) from Wikipedia.

So, there you have it. Not only does the genus Aa exist, it is still top of the list of all plant genera. If that truly was the goal Heinrich Gustav Reichenbach was aiming for, he certainly has succeeded!

Photos via Wikimedia Commons

Further Reading: [1]

A Newly Described Fungus That Mimics Flowers

(A) Young yellow-orange pseudoflower. (B) Mature pseudoflower. (C) Longitudinal section of an infected X. surinamensis inflorescence. (D) Healthy yellow flower of X. surinamensis shown for comparison. [SOURCE]

Imagine there was a fungus that was able to hijack human reproductive structures so that it could reproduce. Though this sounds like the basis of a strange science fiction story, a similar situation to this has just been described from Guyana between two species of yellow-eyed grass (Xyris setigera & X. surinamensis) and a newly described species of fungus called Fusarium xyrophilum.

Fungi that hijack plant reproductive systems are pretty rare in nature, especially when you consider the breadth of interactions between these two branches on the tree of life. What makes this newly described case of floral hijacking so remarkable is the complexity of the whole process. It all begins when an infected Xyris host begins to produce its characteristically lanky inflorescence.

At first glance, nothing would appear abnormal. The floral spike elongates and the inflorescence at the tip gradually matures until the flowers are ready to open. Even when the “flower” begins to emerge from between the tightly packed bracts the process seems pretty par for the course. Gradually a bright yellow, flower-like structure bursts forth, looking very much like how a bright yellow Xyris flower should look. However, a closer inspection of an infected plant would reveal something very different indeed.

Instead of petals, anthers, and a pistil, infected inflorescences produce what is called a pseudoflower complete with petal-like structures. This pseudoflower is not botanical at all. It is made entirely by the Fusarium fungus. Amazingly, these similarities are far from superficial. When researchers analyzed these pseudoflowers, they found that they are extremely close mimics of an actual Xyris flower in more than just looks. For starters, they produce pigments that reflect UV light in much the same way that actual flowers do. They also emit a complex suite of volatile scent compounds that are known to attract pollinating insects. In fact, at least one of those compounds was an exact match to a scent compound produced by the flowers of these two Xyris species.

So, why would a fungus go through all the trouble of mimicking its hosts flowers so accurately? For sex, of course! This species of Fusarium cannot exist without its Xyris hosts. However, Xyris don’t live forever and for the cycle to continue, Fusarium must go on to infect other Xyris individuals. This is where those pseudoflowers come in. Because they so closely match actual Xyris flowers in both appearance and smell, pollinating bees treat them just like flowers. The bees land on and investigate the fungal structure until they figure out there is no reward. No matter, they have already been covered in Fusarium spores.

As the bees visit other Xyris plants in the area, they inevitably deposit spores onto each plant they land on. Essentially, they are being coopted by the fungus in order to find new hosts. By mimicking flowers, the Fusarium is able to hijack plant-pollinator interactions for its own reproduction. It is not entirely certain at this point just how specific this fungus is to these two Xyris species. A search for other potential hosts turned up only a single case of it infecting another Xyris. It is also uncertain as to how much of an impact this fungus has on Xyris reproduction. Though the fungus effectively sterilizes its host, researchers did make a point to mention that Xyris populations may actually benefit from having a few infected plants as the pseudoflowers last much longer than the actual flowers and therefore could serve to attract more pollinators to the area over time. Who knows what further investigations into the ecology of this bizarre system will reveal.

Photo Credit: [1]

Further Reading: [1]

The Ancient Green Blobs of the Andes

Photo by Atlas of Wonders licensed under CC BY-NC-ND 2.0

Curious images of these strange green mounds make the rounds of social media every so often. What kind of alien life form is this? Is it a moss? Is it a fungus? The answer may surprise you!

These large, green mounds are comprised of a colony of plants in the carrot family! The Yareta, or Azorella compacta, hails from the Andes and only grows between 3,200 and 4,500 meters (10,500 - 14,750 ft) in elevation. Its tightly compacted growth habit is an adaptation to its high elevation lifestyle. Cushion growth like this helps these plants prevent heat and water loss in these cold, dry, windy environments.

Every so often, these mats erupt with tiny flowers, which must be a sight to behold! Photo by Lon&Queta licensed under CC BY-NC-SA 2.0

As you might imagine, these plants are extremely slow growers. By studying their growth rates over time, experts estimate that individual colonies expand at the rate of roughly 1.5 cm each year. By extrapolating these rates to the measurements of large colonies, we get a remarkable picture of how old some of these plants truly are. Indeed, some of the largest colonies are estimated at over 3000 years old, making them some of the oldest living organisms on the planet!

Sadly, the dense growth of the plant makes it highly sought after as a fuel source. Massive chunks of these plants are harvested with pick axes and burned as a source of heat. Due to their slow growth rate, overharvesting in recent years has caused a serious decline in Yareta populations. Local governments have since enacted laws to protect this species in hopes that it will give colonies the time they need to recover. Indeed, some recovery has already been documented, however, continued monitoring and management will be needed to ensure their populations remain viable into the foreseeable future.

Photo Credits: [1] [2]

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

Book Release Updates!

It’s February, which means In Defense of Plants: An Exploration into the Wonder of Plants comes out this month!! I just wanted to give you all an update on when orders will start shipping.

Due to shipping delays, physical book orders will not begin shipping until February 23rd from all retailers. I apologize for the week-long delay, but COVID has done a number on shipping logistics and the publisher is doing all they can. Stay patient and you will get it within that week.

Also, for those in Europe, North and South East Asia, Oceania, and Canada that are interested in purchasing a copy, In Defense of Plants will be available in those markets as well! Please stay tuned for more availability info.

That being said, anyone who pre-ordered the audio book or ebook version will receive their copy as scheduled on February 16th.

Finally, a massive thank you to everyone who has pre-ordered the book thus far. Your interest has skyrocketed In Defense of Plants to the top of multiple new release lists! For those of you interested in getting their hands on a copy, here are some links:

Amazon- https://amzn.to/3mBA1Ov

Bookshop- https://bit.ly/3lxih5B

Barnes and Noble- https://bit.ly/3qpE570

A Rare Succulent Member of the Milkweed Family

Photo by: Gennaro Re

Across nearly every ecosystem on Earth, biodiversity tends to follow a pattern in which there are a small handful of very common species and many, many more rare species. It would seem our knowledge of plants follows a similar pattern; we know a lot about a small group of species and very little to nothing about most others. Take, for example, a succulent relative of the milkweeds known to science as Whitesloanea crassa. Despite its occurrence in specialist succulent plant collections, we know next to nothing about the natural history of this species or if it even still exists in the wild at all.

Without flowers, one would be hard pressed to place this odd succulent within a family. Even when in bloom, proper analysis of its taxonomic affinity requires a close inspection of the floral morphology. What W. crassa exhibits is a highly derived morphology well-adapted to its xeric environment. Native to Somalia, it was said to grow on bare ground and its appearance supposedly matches the rocks that dominate its desert habitat. Never producing leaves or branches, the main body of W. crassa consists of a succulent, quadrangular stem that slowly grows upwards as it ages.

Flowers are produced in a dense inflorescence, which is most often situated near the base of the plant. Each flower is very showy at maturity, consisting of a fleshy, fused, 5-lobed corolla decorated in shades of pink and red. As far as I can tell, this is not one of stinkier members of the family. Though I have found pictures of flowers crawling with maggots, most growers fail to comment on any strong odors. In fact, aside from limited care instructions, detailed descriptions of the plant represent the bulk of the scientific information available on this odd species.

Maggots crawling around inside the flowers indicates this species mimics carrion as its pollination mechanism. Photo by: Flavio Agrosi

As I mentioned, it is hard to say whether this species still exists in the wild or not. The original mention of this plant in the literature dates back to 1914. A small population of W. crassa was found in northern Somalia and a few individuals were shipped overseas where they didn’t really make much of an impact on botanists or growers at that time. It would be another 21 years before this plant would receive any additional scientific attention. Attempts to relocate that original population failed but thanks to a handful of cultivated specimens that had finally flowered, W. crassa was given a proper description in 1935. After that time, W. crassa once again slipped back into the world of horticultural obscurity.

A few decades later, two additional trips were made to try and locate additional W. crassa populations. Botanical expeditions to Somalia in 1957 and again in 1986 did manage to locate a few populations of this succulent and it is likely that most of the plants growing in cultivation today are descended from collections made during those periods. However, trying to find any current information on the status of this plant ends there. Some say it has gone extinct, yet another species lost to over-collection and agriculture. Others claim that populations still exist but their whereabouts are kept as a closely guarded secret by locals. Though such claims are largely unsubstantiated, I certainly hope the latter is true and the former is not.

Photo by: Flavio Agrosi

Our knowledge of W. crassa is thus restricted to what we can garner from cultivated specimens. It is interesting to think of how much about this species will remain a mystery simply because we have been unable to observe it in the wild. Despite these limitations, cultivation has nonetheless provided brief windows into it’s evolutionary history. Because of its rock-like appearance, it was assumed that W. crassa was related to the similar-looking members of the genus Pseudolithos. However, genetic analysis indicates that it is not all that closely related to this genus. Instead, W. crassa shares a much closer relationship to Huernia and Duvalia.

This is where the story ends unfortunately. Occasionally one can find cultivated individuals for sale and when you do, they are usually attached to a decent price tag. Those lucky enough to grow this species successfully seem to hold it in high esteem. If you are lucky enough to own one of these plants or to have at least laid eyes on one in person, cherish the experience. Also, consider sharing said experiences on the web. The more information we have on mysterious species like W. crassa, the better the future will be for species like this. With any luck, populations of this plant still exist in the wild, their locations known only to those who live nearby, and maybe one day a lucky scientist will finally get the chance to study its ecology a little bit better.

Photo Credits: [1] & Flavio Agrosi [2] [3] [4]

Further Reading: [1] [2]

Krassilovia: An Amazing Cretaceous Conifer

Reconstructing extinct organisms based on fossils is no simple task. Rarely do paleontologists find complete specimens. More often, reconstructions are based on fragments of individuals found either near one another or at least in similar rock formations. This is especially true for plants as their growth habits frequently result in fragmentary fossilization. As such, fossilized plant remains of a single species are often described as distinct species until subsequent detective work pieces together a more complete picture.

Such was the case for the fossil remains of what were described as Krassilovia mongolica and Podozamites harrisii. Hailing from the Early Cretaceous (some 100-120 million years ago), Krassilovia was only known from oddly spiny cone scales and Podozamites was only known from strap-shaped leaves found in a remote region of Mongolia. Little evidence existed to suggest they belonged to the same plant. That is, until these structures were analyzed using scanning electron micrographs.

(A–C) Articulated seed cones, (D) Isolated cone axis, (E) Incomplete leafy shoot showing a cluster of three attached leaves, (F) Three detached strap-shaped leaves, G) Detail of A showing tightly imbricate interlocking bract-scale complexes, (H) Detail of leaf apex showing converging veins, (I) Three isolated bract-scale complexes showing abaxial (top) and adaxial (bottom) surfaces, (J) Two isolated seeds showing narrow wings. [SOURCE]

These fossilized plant remains were preserved in such detail that microscopic anatomical features such as stomata were visible under magnification. By studying the remains of these plants as well as others, scientists discovered some amazing similarities in the stomata of Krassilovia and Podozamites. Unlike other plant remains associated with those formations, the Krassilovia cone scales and Podozamites leaves shared the exact same stomate morphology. Though not without some uncertainty, the odds that these two associated structures would share this unique morphological trait by chance is slim and suggests that these are indeed parts of the same plant.

The amazing discoveries do not end with stomata either. After countless hours of searching, fully articulated Krassilovia cones were eventually discovered, which finally put the strange spiky cone scales into context. It turns out those spiked scales interlocked with one another, with the two bottom spikes of one scale interlocking with the three top spikes of the scale below it. In life, such interlocking may have helped protect the developing seeds within until they had matured enough to be released. Also, the sheer volume of cone scales coupled with other minute anatomical details I won’t go into here indicate that, similar to Abies and Cedrus cones, Krassilovia cones completely fell apart when fully ripe.

Though not related, the cone scales of the extinct Krassilovia (left) show similarities with the cone scales of modern day Cryptomeria species (right).

Interestingly, the ability to resolve microscopic structures in these fossils has also provided insights into some modern day taxonomic confusion. It turns out that Krassilovia shares many minute anatomical similarities with present day Gnetales. Gnetales really challenge our perception of gymnosperms and their superficial resemblance to angiosperms have led many to suggest that they represent a clade that is sister to flowering plants. However, more recent molecular work has placed the extant members of Gnetales as sister to the pines. Evidence of shared morphological features between extinct conifers like Krassilovia and modern day Gnetales add some interesting support to this hypothesis. Until more concrete evidence is described and analyzed, the true evolutionary relationships among these groups will remain the object of heated debate for the foreseeable fture.

What we can say is that Krassilovia mongolica was one remarkable conifer. Its unique morphology clearly demonstrates that conifers were once far more diverse in form and function than they are currently. Even the habitat in which Krassilovia once lived is not the kind of place you can find thriving conifer communities today. Krassilovia once grew in a swampy habitat. However, whereas only a few extant conifers enjoy swamps, Krassilovia once shared its habitat with a wide variety of conifer species, the likes of which we are only just beginning to appreciate. I for one am extremely excited to see what new fossil discoveries will uncover in the future.

LISTEN TO EPISODE 300 OF THE IN DEFENSE OF PLANTS PODCAST TO LEARN MORE ABOUT THIS FOSSIL AND THE ECOSYSTEM IN WHICH IT ONCE EXISTED.

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

Further Reading: [1]

Fraser Fir: A New Look at an Old Friend

Photo by James St. John licensed under CC BY 2.0

Growing up, Fraser fir (Abies fraseri) was a fairly common sight in our house. Each winter this species would usually win out over other options as the preferred tree for our living room during the holiday season. Indeed, its pleasing shape, lovely color, and soft needles have made it one of the most popular Christmas trees around the world. Amazingly, despite its popularity as a decoration, Fraser fir is so rare in the wild that it is considered an endangered species.

Fraser fir is native to only a handful of areas in the southern Appalachian Mountains. Together with red spruce (Picea rubens), this conifer makes up one of the rarest ecosystems on the continent - the southern Appalachian spruce-fir forest. Such forests only exist at elevations above 4,000 ft (1,200 m) from southwestern Virginia to western North Carolina and eastern Tennessee. The reason for this limited distribution is rooted in both modern day climate and North America’s glacial past.

USGS/Public Domain

Whereas anyone hiking through Appalachian spruce-fir forests could readily draw similarities to boreal forests found farther north, the Appalachian spruce-fir forests are nonetheless unique, hosting many species found nowhere else in the world. Indeed, these forests are holdovers from the Pleistocene when the southeast was much cooler than it is today. As glaciers retreated and the climate warmed, Appalachian spruce-fir forests “retreated” up the mountains, following their preferred climate zones until they hit the peaks of mountains and couldn’t go any further.

Indeed, Fraser fir is in large part limited in its distribution by temperature. This conifer does not perform well at high temperatures and is readily out-competed by other species under warmer conditions. Another factor that has maintained Appalachian spruce-fir forests at elevation is fog. The southern Appalachian Mountains host eastern North America’s only temperate rainforest and fog commonly blankets high elevation areas throughout the year. Research has shown that in addition to keeping these areas cool, fog also serves as an important source of water for Fraser fir and its neighbors. As fog condenses on its needles, these trees are able to absorb that water, keeping them hydrated even when rain is absent.

A view of an Appalachian spruce-fir forest from the Blue Ridge Parkway.

Due to its restricted habitat, Fraser fir has never been extremely common. However, things got even worse as Europeans colonized North America. Over the past two centuries, unsustainable logging and grazing practices have decimated southern Appalachian spruce-fir forests, fragmenting them into even smaller patches with no connectivity in between. In areas where thin, rocky soils were not completely washed away, Fraser fir seedlings did return, however, this was not always the case. In areas where soils were were lost, southern Appalachian spruce–fir forests were incapable of regenerating.

If the story ended there, Fraser fir and its habitat would still be in trouble but sadly, things only got worse with the introduction of the invasive balsam woolly adelgid (Adelges piceae) from Europe around 1900. Like the hemlock woolly adlegid, this invasive, sap-feeding insect has decimated Fraser fir populations throughout southern Appalachia. Having shared no evolutionary history with the adelgid, Fraser fir is essentially defenseless and estimates suggest that upwards of 90% of infect trees have been killed by the invasion. Although plenty of Fraser fir seedlings have sprung up in the wake of this destruction, experts fear that as soon as those trees grow large enough to start forming fissures in their bark, the balsam woolly adelgid will once again experience a massive population boom and repeat the process of destruction again.

Dead Fraser fir as seen from Clingman’s Dome. Photo by Brian Stansberry licensed under CC BY 3.0

The loss of Fraser fir from this imperiled ecosystem has had a ripple effect. Fraser fir is much sturdier than its red spruce neighbors and thus provides an important windbreak, protecting other trees from the powerful gusts that sweep over the mountain tops on a regular basis. With a decline in the Fraser fir canopy, red spruce and other trees are more susceptible to blowdowns. Also, the dense, evergreen canopy of these Appalachian spruce-fir forests produces a unique microclimate that fosters the growth of myriad mosses, liverworts, ferns, and herbs that in turn support species like the endangered endemic spruce-fir moss spider (Microhexura montivaga). As Fraser fir is lost from these areas, the species that it once supported decline as well, placing the whole ecosystem at risk of collapse.

The moss-dominated understory of an Appalachian spruce-fir forest supports species found nowhere else in the world. Photo by Miguel.v licensed under CC BY 3.0

Luckily, the plight of this tree and the habitat it supports has not gone unnoticed by conservationists. Numerous groups and agencies are working on conserving and restoring Fraser fir and southern Appalachian spruce-fir forests to at least a portion of their former glory. This is not an easy task by any means. Aside from lack of funding and human power, southern Appalachian spruce-fir forest conservation and restoration is hindered by the ever present threat of a changing climate. Fears that the life-giving fog that supports this ecosystem may be changing make it difficult to prioritize areas suitable for reforestation. Also, the continued threat from invasive species like the balsam woolly adelgid can hamper even the best restoration and conservation efforts. Still, this doesn’t mean we must give up hope. With continued collaboration and effort, we can still ensure that this unique ecosystem has a chance to persist.

Please visit the Central Appalachian Spruce Restoration Initiative (CASRI) website to learn more!

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

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

Insect Egg Killers

© Copyright Walter Baxter and licensed under CC BY-SA 2.0

Plants and herbivores are engaged in an evolutionary arms race hundreds of millions of years in the making. As plants evolve mechanisms to avoid being eaten, herbivores evolve means of overcoming those defenses. Our understanding of these dynamics is vast but largely focused on the actual act of an organism consuming plant tissues. However, there is growing evidence that plants can take action against herbivores before they are even born.

Taking out herbivores before they even have a chance to munch on a plant seems like a pretty effective means of defense. Indeed, for a growing number of plant species, this starts with the ability to detect insect eggs deposited on or in leaves and stems. As Griese and colleagues put it in their 2020 paper, “Every insect egg being detected and killed, is one less herbivorous larva or adult insect feeding on the plant in the near future.” Amazingly, such early detection and destruction has been found in a variety of plant lineages from conifers to monocots and eudicots.

Gumosis in cherries is a form of defense. Photo by Rosser1954/Public Domain

There are a few different ways plants go about destroying the eggs of herbivores. For instance, upon detecting eggs on their leaves, some mustards will begin to produce volatile compounds that attract parasitoid wasps that lay their eggs on or in the herbivore’s eggs. For other plants, killing herbivore eggs involves the production of special egg-killing compounds. Research on cherry trees (Prunus spp.) has shown that as cicadas push their ovipositor into a twig, the damage induces the production of a sticky gum that floods the egg chamber and prevents the eggs from hatching. Similarly, resin ducts full of insect-killing compounds within the rinds of mangoes will rupture when female flies insert their ovipositor, killing any eggs that are deposited within.

One of the coolest and, dare I say, most badass ways of taking out herbivore eggs can be seen in a variety of plants including mustards, beans, potatoes, and even relatives of the milkweeds and involves a bit of sacrifice on the plant end of things. Upon detecting moth or butterfly eggs, leaf cells situated directly beneath the eggs initiate a defense mechanism called the “hypersensitive response.” Though normally induced by pathogenic microbes, the hypersensitive response appears to work quite well at killing off any eggs that are laid.

“Leaves from B. nigra treated with egg wash of different butterfly species and controls inducing or not a HR-like necrosis. Pieris brassicae (P. b.), P. mannii, (P. m.), P. napi (P. n.), and P. rapae (P. r.) and Anthocharis cardamines (A. c.) induce a strong HR-like necrosis. Egg wash of G. rhamni (G. r.) and Colias sp. (C. sp.) induces a very faint response resembling a chlorosis and does not fit into the established scoring system (faintness indicates 1, but showing up on both sides of the leaf indicates 2).” [SOURCE]

Once eggs are detected, a signalling pathway within the leaf ramps up the production of highly reactive molecules called reactive oxygen species. These compounds effectively kill all of the cells upon which the butterfly eggs sit. The death of those plant cells is thought to change the microclimate directly around the eggs, causing them to either dry up or fall off. These forms of plant defense don’t stop once the eggs have been killed either. There is evidence to suggest that the hypersensitive response to insect eggs also induces these plants to begin producing even more anti-feeding compounds, thus protecting the plants from any herbivores that result from any eggs that weren’t killed.

Plants may be sessile but they are certainly not helpless. Defense mechanisms like these just go to show you how good plants can be at protecting themselves. Certainly, the closer we look at interactions like these, the more we will discover about the amazing world of plant defenses.

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

Further Reading: [1] [2]

Dwarf Sumac: North America's Rarest Rhus

James Henderson, Golden Delight Honey, Bugwood.org.

In honor of my conversation with Anacardiaceae specialist, Dr. Susan Pell, I wanted to dedicate some time to looking at a member of this family that is in desperate need of more attention. I would like you to meet the dwarf sumac (Rhus michauxii). Found only in a few scattered locations throughout the Coastal Plain and Piedmont regions of southeastern North America, this small tree is growing increasingly rare.

Dwarf sumac is a small species, with most individuals maxing out around 1 - 3 feet (30.5 – 91 cm) in height. It produces compound fuzzy leaves with wonderfully serrated leaflets. It flowers throughout early and mid-summer, with individuals producing an upright inflorescence that is characteristic of what one might expect from the genus Rhus. Dwarf sumac is dioecious, meaning individual plants produce either male or female flowers. Also, like many of its cousins, dwarf sumac is highly clonal, sending out runners in all directions that grow into clones of the original. The end result of this habit is large populations comprised of a single genetic individual producing only one type of flower.

Current range of dwarf sumac (Rhus michauxii). Green indicates native presence in state, Yellow indicates present in county but rare, and Orange indicates historical occurrence that has since been extirpated. [SOURCE]

Research indicates that the pygmy sumac was likely never wide spread or common throughout its range. Its dependence on specific soil conditions (namely sandy or rocky, basic soils) and just the right amount of disturbance mean it is pretty picky as to where it can thrive. However, humans have pushed this species far beyond natural tolerances. A combination of agriculture, development, and fire sequestration have all but eliminated most of its historical occurrences.

Today, the remaining dwarf sumac populations are few and far between. Its habit of clonal spread complicates matters even more because remaining populations are largely comprised of clonal offshoots of single individuals that are either male or female, making sexual reproduction almost non-existent in most cases. Also, aside from outright destruction, a lack of fire has also been disastrous for the species. Dwarf sumac requires fairly open habitat to thrive and without regular fires, it is readily out-competed by surrounding vegetation.

A female infructescence. Photo by Alan Cressler

Luckily, dwarf sumac has gotten enough attention to earn it protected status as a federally listed endangered species. However, this doesn’t mean all is well in dwarf sumac land. Lack of funding and overall interest in this species means monitoring of existing populations is infrequent and often done on a volunteer basis. At least one study pointed out that some of the few remaining populations have only been monitored once, which means it is anyone’s guess as to their current status or whether they still exist at all. Some studies also indicate that dwarf sumac is capable of hybridizing with related species such as whinged sumac (Rhus copallinum).

Another complicating factor is that some populations occur in some surprisingly rundown places that can make conservation difficult. Because dwarf sumac relies on disturbance to keep competing vegetation at bay, some populations now exist along highway rights-of way, roadsides, and along the edges of artificially maintained clearings. While this is good news for current population numbers, ensuring that these populations are looked after and maintained is a difficult task when interests outside of conservation are involved.

Some of the best work being done to protect this species involves propagation and restoration. Though still limited in its scope and success, out-planting into new location in addition to augmenting existing populations offers hope of at least slowing dwarf sumac decline in the wild. Special attention has been given to planting genetically distinct male and female plants into existing clonal populations in hopes of increasing pollination and seed set. Though it is too early to count these few attempts as true successes, they do offer a glimmer of hope. Other conservation attempts involve protecting what little habitat remains for this species and encouraging better land management via prescribed burns and invasive species removal.

The future for dwarf sumac remains uncertain, but that doesn’t mean all hope is lost. With more attention and research, this species just may be saved from total destruction. The plight of species like the dwarf sumac serve as an important reminder of why both habitat conservation and restoration are so important for slowing biodiversity loss.

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

Further Reading: [1] [2] [3]James Henderson, Golden Delight Honey, Bugwood.org.

In Defense of Plants Book Coming February 2021!

I am extremely excited to announce that I have written a book! In Defense of Plants: An Exploration Into the Wonder of Plants is slated for release on February 16th, 2021 wherever books are sold.

“In Defense of Plants changes your relationship with the world from the comfort of your windowsill.

The ruthless, horny, and wonderful nature of plants. Understand how plants evolve and live on Earth with a never-before-seen look into their daily drama. Inside, Candeias explores the incredible ways plants live, fight, have sex, and conquer new territory. Whether a blossoming botanist or a professional plant scientist, In Defense of Plants is for anyone who sees plants as more than just static backdrops to more charismatic life forms.

In this easily accessible introduction to the incredible world of plants, you'll find:

• Fantastic botanical histories and plant symbolism

• Passionate stories of flora diversity and scientific names of plant organisms

• Personal tales of discovery through the study of plants

If you enjoyed books like The Botany of Desire, What a Plant Knows, or The Soul of an Octopus, then you'll love In Defense of Plants.”

You can pre-order In Defense of Plants here:

Amazon- https://amzn.to/3mBA1Ov

Bookshop- https://bit.ly/3lxih5B

Barnes and Noble- https://bit.ly/3qpE570

Insect Killer, Plant Symbiont

There has been an uptick in conversations about plant-fungal interactions recently. News of trees communicating via a vast subterranean network of fungal threads has everyone looking at forests like one big commune. Though it feels nice to think of these relationships as altruistic, such simplified takes on the subject overlook the fact that plants and the mycorrhizal fungi they partner with have entered into a mutual exchange, allowing each player to gain from the interaction.

The reciprocity of these relationships are exquisitely illustrated in the partnering of fungi in the genus Metarhizium and their botanical hosts. Metarhizium are predominantly insect pathogens, invading the bodies of soil-dwelling insects, killing them, and absorbing nutrients like nitrogen that are locked up within their tissues. Though extremely good at obtaining compounds like nitrogen from insects, these fungi can not readily access the carbon they need to survive. That is where plants come in.

Plants are experts at producing carbon-based compounds. Via photosynthesis, they break apart CO2 molecules and turn them into carbon-rich sugars for food. However, they need nitrogen to do this. Unfortunately for plants, most of the nitrogen on our planet is locked up in forms they can’t readily access. It is likely that plants’ relative inefficiency at obtaining the nitrogen they need to survive is a major driving force for the partnering between plants and soil-dwelling fungi.

A beetle grub infected by a Metarhizium fungus. Photo by CSIRO (CC BY 3.0)

Over the last few years, scientists studying the relationship between Metarhizium and plants have discovered that a fascinating and ecologically important exchange has evolved among these organisms. When plants are presented with adequate nitrogen, many species will end up over-producing carbohydrates. Their fungal partners are the ones to benefit from this as those excess carbohydrates are fed to the fungi living on or in the plants’ roots. Indeed, via some complex experiments using isotopes of carbon and nitrogen, scientists were able to demonstrate that killing and eating insects isn’t the only way Metarhizium fungi make a living.

In addition to eating insects, Metarhizium also form mycorrhizal relationships with the roots of numerous plant species from grasses to beans. In doing so, they are able to obtain carbohydrates. However, the plants aren’t giving their photosynthates away for free. In exchange, the fungi are providing them with ample nitrogen that was obtained by infecting and digesting their insect prey. By tracing the path of carbon and nitrogen isotopes between fungi and plants, scientists found that the fungi were supplying the plants directly with insect-derived nitrogen.

This may not sound terribly surprising. After all, this is more or less how most mycorrhizal interactions work. However, the fact that an insect-killing fungus is transferring nitrogen from insect to plant directly, rather than from already decomposed materials in the soil reveals a rather novel pathway in the nitrogen cycle of our planet. Metarhizium is an extremely common and widespread genus of fungi and it is likely that these relationships are not unique to the plants used in these studies. The wide-spread nature of these relationships means that this way of cycling nitrogen and carbon through an ecosystem is also extremely common and wide spread.

It is important to remember that relationships like these are a benefit to plants and fungi alike (sorry insects). Both parties stand to gain from the mutualism. It isn’t that plants are plugging into this system and using it to help each other out. To me, it makes far more sense that fungi like Metarhizium benefit from keeping as many healthy plants in their network as possible. We can’t forget that like plants, fungi are organisms fighting to survive long enough to get their genes into the next generation. Mutualisms are not altruisms. They are mutual exchanges that benefit both parties.

Photo Credits: [1] [2]

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

A Tree That Makes Poisonous Rats

For many organisms, poisons are an effective means to keep from being eaten. However, making poisons can be costly. Depending on the compounds involved, poison synthesis can require a lot of nutrients that could be directed elsewhere. This is why some animals acquire poisons through their diet. Take, for instance, the monarch butterfly. As its caterpillars feed on milkweed, they sequester the milkweed toxins in their tissues, which makes them unpalatable into adulthood. Cases like this abound in the invertebrate world, but recently scientists have confirmed that at least one mammal has evolved a similar strategy.

Meet the African crested rat (Lophiomys imhausi). Its large size and bold color patterns make it look like the result of a passionate encounter between a porcupine and a skunk. However, it is 100% rat and it has a fascinating defense strategy that begins with a tree native throughout parts of eastern Africa aptly referred to as the poison arrow tree (Acokanthera schimperi).

An African crested rat displaying its crest of toxic hairs and aposematic color pattern. [SOURCE]

The poison arrow tree is a member of the milkweed family (Apocynaceae), and like many of its relatives, this species produces potent toxins that can cause heart failure. The toxic nature of this tree has not been lost on humans. In fact, the particular strain of toxin it produces is referred to as ouabaïne or “arrow poison” as indigenous peoples have been coating their arrows with its sap for millennia. It turns out that humans aren’t the only mammals to find use for this sap either. The African crested rat uses it too.

The African crested rat grows highly specialized crest of hairs along its back. These hairs are thick and porous and when the rat feels threatened, it erects the crest and shows off its stark black and white coloring. It has been noted in the past that predators such as dogs that try to eat the rat run the risk of collapsing into convulsions and dying so the idea was put forth that that crest of hairs was toxic. Only recently has this been confirmed.

By studying a group of these rodents, scientists observed an interesting behavior. Many of the rats in their study would chew and lick twigs and branches of the poison arrow tree and then chew and lick their crest. What this behavior does is transfer the plant toxins onto those specialized hairs. The high surface area of each hair means they can soak up a lot of the toxins. Surprisingly, the rats appear to be resistant to the sap’s toxic effects. Perhaps they possess modified sodium pumps in their heart muscles that counter the effects of the toxin. Or, they may possess a highly specialized gut flora that breaks down the toxins. Either way, the rats do not show any signs of poisoning from this behavior.

A close-up view of the African crested rat’s poison anointed hairs. Photo by Sara B. Weinstein

The rats don’t have to do this very often to remain poisonous. By talking with locals that still use the poison arrow tree sap on their arrows, researchers learned that the compounds are extremely stable. Once coated, arrows will remain toxic for years. As such, the African crested rat likely doesn’t need constant application for this defense mechanism to remain effective.

As far as we know, this is the first example of a mammal sequestering plant toxins as a form of defense. It is amazing to think that a defense strategy evolved by a plant to avoid being eaten can be co-opted by a rat so that it too can avoid being eaten. Sadly, it is feared that this unique relationship between rat and tree is starting to disappear. Though more research is needed to accurately assess their numbers, there is growing evidence that African crested rats are on the decline. Hopefully with a bit more attention, these trends can be properly assessed and conservation measures can be put into place. In the meantime, please avoid putting any and all rats in your mouth.

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

Further Reading: [1]

How Overharvesting is Changing an Alpine Plant in China

[Source]

We are increasingly becoming aware of the importance of camouflage in the plant kingdom. By blending in with their surroundings, some plants are able to avoid attention from hungry herbivores. Amazingly, a recent investigation in Hengduan Mountains of southwest China has revealed that it can also help plants avoid being harvested for the herbal trade.

Fritillaria delavayi is a tiny, alpine plant that grows among the rocky scree at high elevations in the Hengduan Mountains. It is a slow growing plant that can take upwards of 5 years to produce its first flower. It is also variable in its overall coloration. Some populations consist of plants with green leaves and bright yellow flowers, whereas other populations consist of plants with leaves and flowers in various shades of brown that cause them to blend in with the surrounding rock.

Variation in plant coloration is not terribly novel. Many plant populations can differ from one another in their overall appearance, however, there seems to be a pattern among F. delavayi. It would seem that plants growing in more accessible places tend to be brown whereas plants growing in less accessible places tend to be green and yellow. Interestingly, herbivores don’t seem to explain these differences. Indeed, F. delavayi is chock full of toxic alkaloids that deter what few herbivores exist at such high elevations. Nonetheless, it is the presence of those alkaloids that explain why populations differ so much from one area to the next.

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(A and B) Normal green individuals in populations with low harvest pressure. (C and D) Camouflaged individuals in populations with high harvest pressure [SOURCE]

Because of their purported medicinal value, the demand for F. delavayi bulbs has greatly increased over time. Each year more and more people are heading to these mountains to harvest the plants to sell them in herbal markets. This led a team of researchers to investigate if harvesting by humans could explain color variations among populations.

Amazingly, it did! By looking at ease of access and harvesting, researchers found that plants that were in hard to reach areas or places where harvesting is difficult were more likely to have bright green leaves and yellow flowers. By contrast, plants in easy to reach locations that were not difficult to harvest were more likely to be brown. The researchers even went the extra mile and tested how easily plants of each coloration could be found by humans. Not surprisingly, it took humans much longer to find brown plants that it did for them to find green plants.

Based on their findings, researchers have concluded that harvesting pressures are changing F. delavayi populations in the Hengduan Mountains. Because they are harder to detect and therefore less likely to be harvested, plants sporting the brown coloration are far more likely to survive and reproduce in highly trafficked areas, resulting in an increase in camouflaged offspring. Alternatively, populations growing in hard to reach areas do not experience such heavy selection pressures and can continue to safely sport bright green leaves and yellow flowers. It just goes to show you that human activities can often have unintended consequences for other species. This research also raises the question of how humans have shaped the defensive strategies of other highly sought after plant species.

Photo Credits: [1] [2]

Further Reading: [1]

A Remarkable Floral Radiation on Hawai'i

Ohaha (Brighamia rockii)

Hawai’i is home to so many interesting species of plants, many of which are found nowhere else in the world. One group however, stands out among the rest in that it represents the largest plant radiation not just in Hawai’i, but on any island archipelago!

I am of course talking about the Hawaiian lobelioids (Campanulaceae). Many of you will be familiar with members of the genus Lobelia, which include the lovely cardinal flower (Lobelia cardinalis) and the great blue lobelia (Lobelia siphilitica), but the 6 genera that comprise the Hawaiian radiation are something quite different altogether.

'Oha Wai (Clermontia samuelii). Photo by Forest and Kim Starr licensed under CC BY 2.0

Numbering roughly 125 species in total (in addition to many extinct species), it was long thought that the diversity of Hawaiian lobelioids were the result of at least 3 separate dispersal events. Thanks to recent DNA analysis, it is now believed that all 6 genera are the result of one single dispersal event by a lobelia-like ancestor. This may seem ridiculous but when you consider the fact that this invasion happened back when Gardner Pinnacles and French Frigate Shoals were actual islands and none of the extant islands even existed, then you can begin to grasp the time scales involved that produced such a drastic and varied radiation.

Delissea sp.

Sadly, like countless Hawaiian endemics, the invasion of the human species has spelled disaster. Hawaiian endemics are declining at an alarming rate due to threats like introduced pigs and rats that eat seeds, devour seedlings, and even go as far as to chew right through the stems of adult plants. To make matters worse, many species evolved to a specific suite of pollinators.

ʻŌlulu (Brighamia insignis)

Take, for instance, the case of the ʻŌlulu (Brighamia insignis). It is believed to have evolved a pollination syndrome with a species of sphinx moth known as the fabulous green sphinx moth (Tinostoma smaragditis), which is also believed to be extinct. Similarly, the ʻŌhā wai nui (Clermontia arborescens) evolved for pollination by the island's endemic honey creepers. Due to avian malaria and other human impacts, many honey creepers are endangered and some have already gone extinct. Without their pollinators, many of these lobelioids are doomed to slow extinction if they haven't disappeared already.

While it may be too late to bring back species that have likely gone extinct, that doesn’t mean conservation of these incredible plants is off the table. Indeed, many efforts are being put forth by institutions like the National Tropical Botanical Garden and the Chicago Botanic Gardens to help conserve and restore some of these species. Along the way, the Hawaiian lobelioids are teaching us important and timely lessons on the need for understanding and protecting all pieces of Earth’s ecosystems, rather than individual parts in isolation.

LISTEN TO EPISODE 291 OF THE IN DEFENSE OF PLANTS PODCAST TO LEARN MORE ABOUT LOBELIOID CONSERVATION IN HAWAI’I

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

Further Reading: [1] [2]

Why Plant Relationships Matter for Caterpillars

Photo by Judy Gallagher licensed under CC BY 2.0

When it comes to caterpillars, plant diversity matters. By studying nearly 30,000 plant-caterpillar interactions across three continents (Asia, North America, and Europe), scientists have uncovered important insights into lepidopteran biodiversity in temperate broadleaf forests.

Plants and the caterpillars they host are engaged in an evolutionary arms race. As plants evolve different defenses, caterpillars evolve new ways overcoming them. As you can imagine, studying these intricate relationships can be as fascinating as it is challenging. One could easily spend a lifetime trying to understand the relationships among only a handful of species. However, by taking a step back and asking bigger questions related to evolution and herbivory, scientists have found some interesting patterns than help describe the diversity of plant-caterpillar relationships.

As one might expect, they found that as plant diversity increases, so too does the diversity of caterpillars an ecosystem can support. Many caterpillars specialize on one or only a few different host plants and these are often (though not always) within the same plant family. The reason for this has to do with plant defenses. The more closely related plants are, the more likely they are to share similar defense strategies. For instance, most milkweeds (Asclepias spp.) produce toxic compounds called cardiac glycosides and many different members of the nightshade family (Solanaceae) produce similar suites of toxic alkaloids. As a result, insects that munch on their tissues have similar hurdles to overcome in an evolutionary sense.

The more closely related plants there are in an environment, the more likely it is that the caterpillars they host can jump from one plant species to another. As a result, ecosystems that boast relatively few plant lineages support relatively few caterpillar species in part because the caterpillars they do host can more easily jump from plant species to another. The same logic applies in the opposite direction as well. Ecosystems comprised of a diversity of plant lineages limit the likelihood that any given species of caterpillar can find multiple different hosts. Because each clade of plants produces their own brand of herbivore defenses, the caterpillars hosted by each are also more likely to be different. Thus, as plant diversity goes up, so too do the numbers of caterpillar species an ecosystem can support.

Though not tested by this research, this also provides yet another example of why invasive plants harm biodiversity. Plants from other areas of the world are more likely to present novel defenses to native herbivores. If the caterpillars do not have what it takes to overcome these defenses or simply don’t recognize the plant as food, the fewer caterpillars that ecosystem can support.

Of course, none of this should come as a surprise to those interesting in native plants and gardening. The more indigenous plants you grow in and around your landscape, the more insects you can support. I also firmly believe that the results of this research are not limited to caterpillars. The same pattern likely applies to any number of plant eaters, from microbes to mammals, no matter where you look. What this research gives us are some answers to questions like “why does biodiversity matter?”

Photo Credit: [1]

Further Reading: [1]

The Knife-Edge Economy of Panama's Trash-Basket Treelet

Trade-offs abound in nature. It would be impossible for any organism to evolve a combination of attributes that are ideal under all circumstances. This is especially true for plants. The botanical world’s need to obtain water and nutrients from roots while simultaneously maximizing photosynthetic area often means finding a balance between allocating resources to leaves and roots. This trade-off is made especially apparent in species like Panama’s basurera (Quadrella antonensis), whose name translates to trash basket.

The basurera is a rare treelet endemic to only a few highland locations in Panama where it grows in the dense shade of the rainforest canopy. It earned the name basurera because this tiny tree has adopted a litter trapping lifestyle. The few leaves it produces form a basket-like structure at the tip of its spindly stem. As debris falls from the canopy above, some of it is trapped by basurera’s leafy basket. The fact that basurera collects debris isn’t all that shocking. Many understory plants are saddled with a debris load to one degree or another. The most striking feature of its anatomy can be found by digging around in the litter trapped within its leafy basket.

Even “large” basurera are not that big. [SOURCE]

From its tiny stem and branches emerges numerous adventitious roots. These roots branch out into the humus as it builds up within the basket. Not only do the roots help the treelet to hold onto any litter that falls into the basket, they also function just like roots in the soil. As the roots branch and fork, they produce copious fine root hairs. These root hairs have even been found to associate with arbuscular mycorrhizal fungi! Indeed, the basurera is creating its own soil by trapping litter from above that it can use to obtain nutrients that it can’t get from the soil at its base. However, in using its leaves to do this, this treelet puts a damper on its potential photosynthetic capacity.

As humus develops within the basket, it blocks sunlight from hitting the leaves. As you can imagine, this creates a delicate knife-edge economy in this already shady habitat. By manipulating the amount of humus in the basket, scientists have shown that the basurera relies on that humus for sustenance. When the humus was selectively removed, basurera lack the nutrients needed to produce more leaves. However, as humus builds up, the plant photosynthesizes less and less. It would appear that this species has dealing with a trade-off in assimilating carbon and acquiring other forms of nutrients.

Adventitious roots emerging from the stem of a basurera. [SOURCE]

Research suggests that the shift towards litter trapping likely has to do with the nutrient-poor soils in which the basurera grows. Instead of relying on the ground to provide it with the nutrients it needs, the basurera simply produces its own supply of soil in its leaves. It seems that for this shade-tolerant treelet, obtaining nutrients is more pressing than maximizing photosynthesis. However, in doing so, it is sacrificing growth and reproduction. By studying 112 individuals over the course of a year, scientists found that only 30 basurera actually flowered and, out of those 30, only 10 fruits were produced. Such low reproductive output likely explains why this treelet can only be found in a few areas of Panama. It also makes the basurera extremely vulnerable to disturbance. With slow growth and even slower reproduction, the basurera is at high risk from anything that can reduce population numbers.

Despite its rarity in the highland forests of Panama, the basurera nonetheless offers a window into the economic balance plants must strike as they try to make a living. It just goes to show you that even small, obscure species have a lot to teach us about the evolution of life on our planet.

Photo Credits & Further Reading: [1]

Southern Beeches and Biogeography

If you spend any time learning about paleontology, you are bound to come across at least one reference to the southern beeches (genus Nothofagus). This remarkable and ecologically important group of trees can be found growing throughout the Southern Hemisphere at high latitudes in South America, Australia, New Zealand, New Guinea, and New Caledonia. Not only are they prominent players in the forests in which they grow, their fossil history has provided scientists with invaluable data on plate tectonics and biogeography.

Southern beeches may not be the tallest trees in any forest but that doesn’t mean they aren’t impressive. Numbering around 37 species, southern beeches have conquered a range of climate zones from temperate to tropical. Those living in lowland tropical forests tend to be evergreen, holding onto their leaves throughout the year whereas those living in temperate or montane habitats have evolved a deciduous habit. Some species of southern beech are also known for their longevity, with individuals estimated to be in excess of 500 years in age.

Nothofagus alpina

Anyone familiar with the true beeches (genus Fagus) will quickly recognize many similarities among these genera. From their toothy leaves to their triangular nuts, these trees are strikingly similar in appearance. Indeed, for much of their botanical history, southern beeches were included in the beech family (Fagaceae). However, recent molecular work has revealed that the southern beeches are genetically distinct enough to warrant their own family - Nothofagaceae.

The beech-like fruits of Nothofagus obliqua var. macrocarpa

As mentioned, the southern beeches, both extant and extinct, have been important players in our understanding of plate tectonics. Their modern day distribution throughout the Southern Hemisphere seems to hint at a more concentrated distribution at some point in the past. All of the continents and islands on which they are found today were once part of the supercontinent of Gondwana, which has led many to suggest that the southern beech family arose before Gondwana broke apart during the Jurassic, with ancestors of extant species riding the southern land masses to their modern day positions. Indeed, the paleo record seems to support this quite well.

Fall colors of Nothofagus cunninghamii.

The southern beeches have an impressive fossil record that dates back some 80 million years to the late Cretaceous. Their fossils have been found throughout many of the Southern Hemisphere continents including the now-frozen Antarctica. It would seem that the modern distribution of these trees is the result of plate tectonics rather than the movement of seeds across oceans. This is bolstered by lines of evidence such as seed dispersal. Southern beech nuts are fairly large and do not show any adaptations for long distance dispersal, leading many to suggest that they simply cannot ocean hop without serious help from other forms of life.

Nothofagus fusca

However, life is rarely so simple. Recent molecular work suggests that continental drift can’t explain the distribution of every southern beech species. By studying trees growing in New Zealand and comparing them to those growing in Australia and Tasmania, scientists have discovered that these lineages are far too young to have originated before the breakup of Gondwana. As such, the southern beeches of Austrialasia more likely got to their current distributions via long distance dispersal events. Exactly what allowed their seeds to cross the Tasman Sea is up for debate, but certainly not impossible given the expanse of time available for rare events to occur. Regardless of where anyone stands on this recent evidence, it nonetheless suggests that the biogeographic history of the southern beech family isn’t as clear cut as once thought.

Nothofagus fusca

Unfortunately, while southern beeches hold a prominent place in the minds of naturalists, the same cannot be said for the rest of the world. Little care has been given to their scientific and ecological importance and massive quantities of these trees are logged each and every year. Today it is estimated that 30% of all southern beech species are threatened with extinction. Luckily, large portions of the remaining populations for these trees are growing on protected lands. Also, because of their scientific importance, numerous southern beeches can be found growing in botanical collections and their seeds are well represented in seed banks. Still, southern beeches and the forests they comprise are worthy of respect and protection.

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

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

Floral Trickery of the Bat Plants

Photo by Geoff McKay licensed under CC BY 2.0

Bat plants (genus Tacca) are bizarre-looking plants. Their nondescript appearance when not in flower enshrouds the extravagant and, dare I say macabre appearance of their blooms. The inflorescence of this genus is something to marvel at. The flowers are borne above sets of large, conspicuous bracts and numerous whisker-like bracteoles. Despite their unique appearance and popularity among plant collectors, the pollination strategies utilized by the roughly 20 species of bat plants have received surprisingly little attention over the years.

Bat plants are most at home in the shaded, humid understories of tropical rainforests around the globe (though there are a couple exceptions to this rule). Amazingly, these plants are members of the yam family (Dioscoreaceae) and are thought to be closely related to the equally bizarre Burmanniaceae, a family comprised entirely of oddball parasites. Taxonomic affinities aside, there is no denying that bat plants produce truly unique inflorescences and many a hypotheses has been put forth to explain the function of their peculiar floral displays.

The white bat plant (Tacca integrifolia). Photo by MaX Fulcher licensed under CC BY-NC-SA 2.0

The black bat plant (Tacca chantrieri). Photo by Hazel licensed under CC BY-SA 2.0

The most common of these is that the flowers are an example of sapromyiophily and thus mimic a rotting corpse in both smell and appearance as a means of attracting carrion flies. However, despite plenty of speculation, such hypotheses have largely gone untested. It wasn’t until fairly recently that anyone put forth an attempt to observe pollination of these plants in their natural habitats.

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A) T. leontopetaloides; (B) T. plantaginea; (C) T. parkeri; (D) T. palmatifida; (E) T. palmata; (F) T. subflabellata; (G) T. integrifoliafrom; (H) T. integrifoliafrom; (I) T. ampliplacenta; (J) T. chantrieri. [SOURCE]

A 2005 study done in South Yunnan province, China found that almost nothing visited the flowers of Tacca chantrieri. Despite the presence of numerous potential pollinators, only a handful of small, stingless bees paid any attention to these obvious floral cues. This led the authors to suggest that most bat plants are self-pollinated. Indeed, genetic analysis of different populations of T. chantrieri helped bolster this conclusion by demonstrating that there is very little evidence of genetic transfer between T. chantrieri populations. Yet, this is far from a smoking gun. Strong genetic structuring among populations could simply mean that pollinators aren’t moving very far. Also, if most bat plants simply opt for fertilizing their own blooms, why has this genus maintained such elaborate floral morphology? Needless to say, more work was needed.

Luckily, a recent study from Malaysia has made great strides in our understanding of the sex lives of these plants. By observing 7 different species of bat plant in the wild, researchers were able to collect plenty of data on bat plant pollination. It turns out that the flowers of these 7 species are quite popular with insects. Bat plant floral visitors in their study included everything from tiny, stingless bees to ants, beetles, and weevils. However, the most common floral visitors for most bat plant species were small, biting midges. This is where things get very interesting.

(A–C) Female Forcipomyia biting midge. Arrows indicating pollen grains. [SOURCE]

As their common name suggests, biting midges are most famous for biting other animals. Though they will drink nectar, female biting midges need lots of protein to successfully produce eggs. They meet their protein needs by drinking the blood of insects and mammals. Of the biting midges that most frequently visited bat plant flowers, the most common hail from two groups known to feed exclusively on mammalian blood. Finding these biting midges in high numbers on bat plant flowers raises the question of what they stand to gain from these strange-looking blooms.

The conclusion the authors came to was that bat plant blooms are using a bit of trickery to lure in female midges. They hypothesize that the color patterns of the bracts and flickering motion of whisker-like bracteoles simulates the movements of mammals that the midges normally feed on. It is also possible that bat plant flowers emit volatile scents that enhance this mimicry, though more work is needed to say for sure. What the researchers do know is that the behavior of female biting midges upon visiting a flower is enough to pick up and deposit plenty of pollen as they search for a blood meal that doesn’t exist. How common this floral ruse is among the remaining species is yet to be determined but the similarities in inflorescence structure among members of this genus suggest similar tricks are being played on pollinators wherever bat plants grow.

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

Further Reading: [1] [2]

Floral Pigments in a Changing World

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

Flowers paint the world in a dazzling array of colors. Some of these we can see and others we cannot. Many plants paint their blooms in special pigments that absorb ultraviolet light, revealing intriguing patterns to pollinators like bees and even some birds that can see well into the UV part of the electromagnetic spectrum. UV absorbing pigments do more than attract pollinators. They can also protect sensitive reproductive organs from UV radiation. By studying these pigments, scientists are finding that many different plants are changing their floral displays in response to changes in their environment.

Growing up I heard a lot about the hole in the ozone layer. Prior to the 1980’s humans were pumping massive quantities of ozone-depleting chemicals such as halocarbon refrigerants, solvents, and chlorofluorocarbons (CFCs) into the atmosphere, creating a massive hole in the ozone layer. Though ozone depletion has improved markedly thanks to regulations placed on these chemicals, it doesn’t mean that life has not had to adapt. As you may remember from your grade school science class, Earth’s ozone layer helps protect life from the damaging effects of ultraviolet radiation. UV radiation damages sensitive biological molecules like DNA so it is in any organisms best interest to minimize its impacts.

UV absorbing pigments in floral tissues can do just that. In addition to attracting pollinators, these pigments act as a sort of sun screen, reducing the likelihood of damaging mutations. By studying 1,238 herbarium specimens collected between 1941 and 2017 representing 42 different species, scientists discovered a startling change in the amount of UV pigments produced in their flowers.

Exemplary images for a species with anthers exposed to ambient conditions, Potentilla crantzii (A–C) and a species with anthers protected by floral tissue Mimulus guttatus (D–F). Darker petal areas possess UV-absorbing compounds whereas lighter areas are UV reflective and lack UV-absorbing compounds. (B) and (E) display a reduced area of UV-absorbing pigmentation on petals compared to (C) and (F). Arrows in (E) and (F) highlight differences in pigment distribution on the lower petal lobe of M. guttatus. [SOURCE]

Across North America, Europe, and Australia, the amount of UV pigments produced in the flowers tended to increase by an average of 2% per year from 1941 to 2017. These increases in UV pigments occurred in tandem with decreases in the ozone layer. It would appear that, to protect their reproductive organs from harmful UV rays, many plants were increasing these protective pigments.

However, changes in UV pigments were not uniform across all the species they examined. Plants that produce saucer or cup-shaped flowers experienced the greatest increases in UV pigments. This makes complete sense as this sort of floral morphology exposes the reproductive organs directly to the sun’s rays. The pattern reversed when scientists examined flowers whose petals enclose the reproductive organs such as those seen in bladderworts (Utricularia spp.). UV pigments in flowers that conceal their reproductive organs actually decreased over this time period.

The reason for this comes down to a trade off inherent in UV pigments. Absorbing UV radiation is a great way to reduce its impact on sensitive tissues but it also leads to increased temperatures. For plants that enclose their reproductive organs within their petals, this can lead to overheating. Heat can also be very damaging to floral structures so it makes complete sense that species with this type of floral morphology would demonstrate the opposite pattern. By reducing the amount of UV absorbing pigments in their flowers, plants like bladderworts are able to minimize the effect of increased radiation and temperatures that occurred over this time period.

How changes in floral pigments are affecting pollination rates for these plants is another story entirely. Because UV pigments also help attract certain pollinators, there is always a chance that the appearance of some of these flowers may also be changing over time. Now that we know this is occurring across a wide range of unrelated plants, research can now be aimed at tackling questions like this.

Photo Credits: [1] [2]

Further Reading: [1]

Australia's Stinging Trees Use Animal-Like Venom to Protect Themselves

Photo by o2elot licensed under CC BY-SA 2.0

Australia’s stinging trees (genus Dendrocnide) are no ordinary members of the nettle family (Urticaceae). Whereas a physical encounter with most of their cousins will leave you with a mild burning sensation that usually subsides within a few hours, coming into contact with a stinging tree can leave you with excruciating pain that can last for days. Such a severe reaction to stinging trees has left scientists wondering what is going on chemically that makes these trees so darn painful.

It turns out that the stinging trees have evolved chemical defenses that are surprisingly similar to the venom produced by some spiders. The discovery of these chemicals within the stinging hairs of stinging trees is a first for the plant kingdom and likely represent a remarkable case of convergent evolution.

The structure model of stinging tree venom (left) and the stinging trichomes of D. excelsa (right). [SOURCE]

Stinging tree venom belongs to a class of compounds known as neurotoxins. Their molecular structure looks a lot like a 3D version of a frustrated scribble on a piece of paper. This convoluted structure just so happens to target mammalian pain receptors with high affinity. Once attached, they activate the sensory neurons, forcing them into overdrive. This is why the pain is so severe.

The petioles of D. excelsa are covered in stinging hairs (top). Scanning electron micrograph of trichome structure on the leaf of D. moroides (bottom). [SOURCE]

This neurotoxic venom is delivered into the body thanks to the amazing anatomy of nettle trichomes. These tiny hairs are hollow and attached to the top of a sac-like structure filled with the venom. When something brushes against the hairs, the tips break off, turning them into tiny hypodermic needles. As the victim brushes across a stem or leaf, thousands of these hairs inject minutes amount of venom into the skin. Pain is soon to follow.

Amazingly, not all animals seem to be affected by the stinging trees potent venom. Plenty of creatures from insects to birds and even some mammals will feed on the leaves and fruits of these trees, all of which are covered in venom-filled trichomes. As is always the case in biology, there is no surefire way to deter all potential predators. Inevitably some organism(s) will circumvent the deterrent through evolutionary means. Nonetheless, the discovery of animal-like venom being produced by plants is remarkable and opens up new doors into the world of chemical ecology and evolution.

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

Further Reading: [1]