A Wonderful Hill Prairie

In this episode, we explore a hill prairie situated along the Middle Fork River. Hill prairies are essentially what the sound like but often grow in drought-prone soils.

In this episode we get up close and personal with:

Cylindrical Blazingstar (Liatris cylindracea)

Prairie Dock (Silphium terebinthinaceum)

Whorled Milkwort (Polygala verticillata)

Sideoats Grama (Bouteloua curtipendula)

Producer, Writer, Creator, Host:
Matt Candeias (http://www.indefenseofplants.com)

Producer, Editor, Camera:
Grant Czadzeck (http://www.grantczadzeck.com)


Music by: 
Artist:Snowball II
Track: Hurry

Large Parrots And Their Influence On Amazonian Ecosystems

Parrots, especially the larger species, have long been thought to be a bane to plant reproduction. Anyone that has watched a parrot feed may understand why this has been the case. With their incredible beaks, parrots make short work of even the toughest seeds. However, this assumption is much too broad. In fact, recent research suggests that entire Amazonian ecosystems may have parrots to thank.

Bolivia's Amazonian savannas are remarkable and dynamic ecosystems. These seasonally flooded grasslands are dotted with forest islands dominated by the motacú palm (Attalea princeps). These forest patches are an integral part of the local ecology and have thus received a lot of attention both culturally and scientifically. The dominance of motacú palm poses an intriguing question - what maintains them on the landscape?

The fruits of this palm are quite large and fleshy. Some have hypothesized that this represents an anachronism of sorts, with the large fruit having once been dispersed by now extinct Pleistocene megafauna. Despite this assumption, these forest islands persist. What's more, motacú palms still manage to germinate. Obviously there was more to this story than meets the theoretical eye. As it turns out, macaws seem to be the missing piece of this ecological puzzle. 

Researchers found that three species of macaw (Ara ararauna, A. glaucogularis, and A. severus) comprised the main seed dispersers of this dominant palm species. What's more, they manage to do so over great distances. You see, the palms offer up vast quantities of fleshy fruits but not much in the way of a good perch on which to eat them. Parrots such as macaws cannot take an entire seed down in one gulp. They must manipulate it with their beak and feet in order to consume the flesh. To do this they need to find a perch.

Suitable perches aren't always in the immediate area so the macaws take to the wing along with their seedy meals. Researchers found that these three macaw species will fly upwards of 1,200 meters to perch and eat. Far from being the seed predators they were assumed to be, the birds are actually quite good for the seeds. The fleshy outer covering is consumed and the seed itself is discarded intact. This suggests that preferred perching trees become centers of palm propagation and they have the parrots to thank. 

Indeed, seedling motacú palms are frequently found within 1 - 5 meters of the nearest perching tree. No other seed disperser even came close to the macaws. What's more, introduced cattle (thought to mimic the seed dispersing capabilities of some extinct megafauna) had a markedly negative effect on palm seed germination thanks to issues such as soil compaction, trampling, and herbivory. Taken together, this paints a radically different picture of the forces structuring this unique Amazonian community.

Photo Credits: Wikimedia Commons

Further Reading: [1]

The Squirting Cucumber

Plants have gone to great lengths when it comes to seed dispersal. One of the most bizarre examples of this can be found in an ambling Mediterranean plant affectionately referred to as the squirting cucumber. As funny as this may sound, the name could not be more appropriate. 

Known scientifically as Ecballium elaterium, the squirting cucumber can be found growing along roadsides and other so-called "waste places" from the Mediterranean regions of western Europe and northern Africa all the way to parts of temperate Asia. It is the only member of its genus, which resides in the family Cucurbitaceae. It is a rather toxic species as well, with all parts of the plant producing a suite of chemicals called cucurbitacins. In total, it seems like a rather unassuming plant. It goes through the motions of growing and flowering throughout the summer months but the real show begins once its odd fruits have ripened. 

A cursory inspection would not reveal anything readily different about its fruit. Following fertilization, they gradually swell into modest sized version of the sorts you expect from this family of plants. It's what is going on within the fruit that is rather interesting. As the fruit reaches maturity, the tissues surrounding the seeds begin to break down. The breakdown of this material creates a lot of mucilaginous liquid, causing internal pressure to build. And I mean a lot of pressure. Measurements have revealed that at peak ripening, pressures within the fruit can reach upwards of 27 atm, which is 27 times the amount of atmospheric pressure we experience when standing at sea level!

A cross section of the fruit showing the weakened connection point.

A cross section of the fruit showing the weakened connection point.

At the same time, the attachment point of the stem or "peduncle" begins to weaken. With all that pressure building, it isn't long before something has to give. This is exactly the moment when the squirting cucumber earns its name. The stem breaks away from the fruit, revealing a small hole. Within a fraction of a second, all of that pressurized mucilage comes rocketing outward carrying the precious cargo of seeds with it. 


The result is pretty remarkable. Seeds are launched anywhere from 6 to 20 feet (1 - 6 m) away from the parent plant. This form of dispersal falls under the category of ballistic seed dispersal and it is incredibly effective. Getting away from the competitive environment immediately surrounding your parents is the first step in the success of any plant. The squirting cucumber does just that. It is no wonder then that this is an incredibly successful plant species. 

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

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

Tropical Ferns in Temperate North America

All plants undergo some form of alternation of generations. It is the process in which, through reproduction, they cycle between a haploid gametophyte stage and a diploid sporophyte stage. In ferns and lycophytes, this alternation of generations has been taken to the extreme. Instead of the sporophyte relying on the gametophyte for sustenance, the two generations are physically independent and thus separated from one another. In a handful of fern genera here in North America, this has led to some intriguing and, dare I say, downright puzzling distributions. The presence of a small handful of tropical fern genera in temperate North America has generated multiple scientific investigations since the early 1900's. However, as is constantly happening in science, as soon as we answer one question, seemingly infinite more questions arise. At the very least, the presence of these ferns in temperate regions offers us a tantalizing window into this continents ancient past.

To say any of these ferns offer the casual observer much to look at would be a bit of an exaggeration. They do not play out their lives in typical fern fashion. These out of place tropical ferns exists entirely as asexual colonies of gametophytes, reproducing solely by tiny bundles of cells called gemmae. What's more, you will only find them tucked away in the damp, sheltered nooks and crannies of rocky overhangs and waterfalls. Buffered by unique microclimates, it is very likely that these fern species have existed in these far away corners for a very, very long time. The last time their respective habitats approached anything resembling a tropical climate was over 60 million years ago. Some have suggested that they have been able to hang on in their reduced form for unthinkable lengths of time in these sheltered habitats. Warm, wet air gets funneled into the crevices and canyons where they grow, protecting them from the deep freezes so common in these temperate regions. Others have suggested that their spores blew in from other regions around the world and, through chance, a few landed in the right spots for the persistence of their gametophyte stages.

The type of habitat you can expect to find these gametophytes.

Aside from their mysterious origins, there is also the matter of why we never find a mature sporophyte of any of these ferns. At least 4 species in North America are known to exist this way - Grammitis nimbata, Hymenophyllum tunbridgense, Vittaria appalachiana, and a member of the genus Trichomanes, most of which are restricted to a small region of southern Appalachia. In the early 1980's, an attempt at coaxing sporophyte production from V. appalachiana was made. Researchers at the University of Tennessee brought a few batches of gametophytes into cultivation. In the confines of the lab, under strictly controlled conditions, they were able to convince some of the gametophytes to produce sporophytes. As these tiny sporophytes developed, they were afforded a brief look at what this fern was all about. It confirmed earlier suspicions that it was indeed a member of the genus Vittaria, or as they are commonly known, the shoestring ferns. The closest living relative of this genus can be found growing in Florida, which hints at a more localized source for these odd gametophytes, however, both physiology and subsequent genetic analyses have revealed the Appalachian Vitarria to be a distinct species of its own. Thus, the mystery of its origin remains elusive.

In order to see them for yourself, you have to be willing to cram yourself into some interesting situations. They really put the emphasis on the "micro" part of the microclimate phenomenon. What's more, you really have to know what you are looking for. Finding gametophytes is rarely an easy task and when you consider the myriad other bryophytes and ferns they share their sheltered habitats with, picking them out of a lineup gets all the more tricky. Your best bet is to find someone that knows exactly where they are. Once you see them for the first time, locating other populations gets a bit easier. The casual observer may not understand the resulting excitement but once you know what you are looking at, it is kind of hard not to get some goosebumps. These gametophyte colonies are a truly bizarre and wonderful component of North American flora.

Photo Credit: [1] [2]

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

In Search of the Orange Fringed Orchid

In Defense of Plants is finally back for another exciting botanical adventure! This week we explore another wonderful sand prairie in search of one of North America's most stunning terrestrial orchids - the orange fringed orchid (Platanthera ciliaris). Along the way, we meet a handful of great native plant species that are at home in these sandy soils.

Music by: 
Artist: Eyes Behind the Veil
Track: Folding Chair
Album: Besides

Herbarium Biases

Humans carry countless biases with them wherever they go. Even the logical mind of a scientist is no stranger to prejudice. Identifying such biases in the way we do science is key to improving the discipline and, as computing power and access to big data increases, we are gaining a better understanding of just how prevalent our biases really are. A recent study that looked at herbarium collections around the world aims to do just that.

With herbaria closing shop around the globe, the need to digitize collections has never been more urgent. Although more and more collections are finding their way into digital libraries, a vast majority of herbarium collections risk being lost forever. This alone represents a major bias. Such organismal science has sadly been scoffed at in recent decades. Still, enough collections have been entered into databases that interesting patterns are starting to emerge. A team of researchers recently took a closer look at roughly 5 million digitized floras representing the most complete digital floras from Australia, South Africa, and New England.

In doing so, the team was able to find some startling biases in these collections. They broke them down into a handful of categories with the hope that botanists and ecologists can start to improve on these gaps over the coming decades. Although the floras they examined by no means represent anything close to a complete picture of our floristic understanding of the world, they nonetheless mirror issues that are sure to crop up no matter where collections have been made.

The first major category is that of spatial or geographic bias. This occurs whenever specimens are collected at a higher frequency in one place over another. There are likely many reasons for this - ease of access, proximity to research institutions, just to name a few. The team found that herbarium collections tended to occur in the same areas through time. What's more, they tended to occur more often near roads with a surprising 50% of specimens collected within 2 km of a roadside. This can result in a highly skewed perspective of the kind of taxa represented in a region. Roadside vegetation is comprised of species capable of dealing with runoff, soil compaction, and pollution, and is likely depauperate of taxa less able to handle such conditions. They also found a elevational bias, with a majority of specimens having been collected below 500 meters. 

Maps demonstration spatial biases in herbarium collections. Those in red have more collections and those in blue have fewer collections.

Maps demonstration spatial biases in herbarium collections. Those in red have more collections and those in blue have fewer collections.

The second major category is that of temporal bias. This occurs whenever specimens are collected more frequently during certain parts of the year over others. The team found that collections disproportionately occurred during spring and summer months. As anyone who hikes can tell you, there is a lot of variation among plant communities from season to season and any good collection should sample a location multiple times a year. In addition to seasonal biases, the team also found extreme biases in terms of history. Collections in South Africa and Australia started to rise shortly after World War II and peaked in the 1980's and 1990's respectively. Compare this to New England where peak collections occurred nearly 100 years prior. If we are to track long term trends and changes in the flora of various regions, collections need to occur far more regularly. Obviously institutions have shied away from such investigations in recent decades. Only public interest and funding can reverse such trends, hopefully not before it is too late.

The third major bias they found is that of trait bias. This occurs whenever a collector specifically aims for species with a certain life history characteristic (annual vs. perennial, woody vs. herbacious) as well as species of conservation concern. Indeed, the team found that perennial species were over-represented in most herbarium collections. Also, gramminoids dominated herbarium collections in Australia and South Africa whereas herbs and trees were over-represented in New England. Another interesting pattern that emerged is that short plants had higher representation in harbaria than taller species. Obviously this has a lot to do with ease of collection.

Another pattern that emerged which is of conservation concern is that threatened or endangered species are severely under-represented in herbarium collections. Although care must be taken to not over-collect species whose numbers are dwindling, their lack of representation in herbarium collections can seriously hinder conservation efforts. Such under-represenation can lead to erroneous estimations of species abundances and distributions. It can also hinder our understanding of plant community dynamics.

The fourth major bias is that of phylogenetic bias. Certain clades are more sought after than others. This leads to a disproportionate amount of showy or valuable species turning up in herbaria around the globe. It also leads to an over-representation of potentially "useful" plant species in terms of things like medicines or dyes. This leaves a large portion of regional floras under-sampled. This in turn exacerbates issues relating to our understanding of plant community dynamics and the change in plant abundance and distribution through time.

Finally, the fifth major bias is that of collector bias. This pattern stems from the fact that in all the regions sampled for this study, a majority of the collections were made by only a handful of individuals. This means that all of these collections are the products of the habits and preferences of these collectors. Some collectors may favor sampling the entire flora of a region whereas others may favor certain clades over others. Similarly, some collectors may favor plants with interesting physiologies whereas other may favor plants with peculiar life-histories such as carnivores or succulents.

The use and importance of herbaria has changed a lot over the last two centuries. Whereas they largely started out as a tool for taxonomists, the utility of herbarium collections has since expanded into areas that were never thought possible. With the advent of new technologies, who knows what the future holds. Of course, this means nothing if interest and support for herbarium collections continues to decline. Their utility in the context of research and conservation cannot be understated. We need herbaria now more than ever. Understanding biases is a great step towards improving the discipline. We must aim to improve collections in these so-called cold spots and to avoid as many biases as possible in doing so.

Photo Credits: Wikimedia Commons

Further Reading: [1]


Closed on Account of Weather

Alpine and tundra zones are harsh habitats for any organism. Favorable conditions are fleeting and nasty weather can crop up in the blink of an eye. Whereas animals in these habitats can take cover, plants don't have that luxury. They are stuck in place and have to deal with whatever comes their way. Despite these challenges, myriad plant species have adapted to these conditions and thrive where other plants would perish. The intense selection pressures of these habitats have led to some fascinating evolutionary adaptations, especially when it comes to reproduction.

Take, for instance, the Arctic gentian (Gentianodes algida). This lovely plant can be found growing in alpine and tundra habitats in both North America and Asia. Like most plants of these habitats, the Arctic gentian has a low growth habit, forming a dense cluster of fleshy, narrow leaves that hug the ground. This protects the plant from blustering winds and extreme cold. From late July until early September, when the short growing season is nearly over, this wonderful plant comes into bloom. 

Clusters of white and blue speckled flowers are borne on short stems and, unlike other angiosperms that readily self-pollinate under harsh conditions, the Arctic gentian requires outcrossing to set seed. This can be troublesome. As you can imagine, pollinators can be in short supply in these habitats. What's more, with conditions changing on a dime, the flowers must be able to cope with whatever comes their way. The Arctic gentian is not helpless though. It has an interesting adaptation to these habitats and it involves movement.

Only a handful of plant species are known for their ability to move their various organs with relative rapidity. This gentian probably doesn't make that list very often. However, it probably should as its flowers are capable of responding to changes in weather by closing up shop. It is not alone in this behavior. Plenty of plant species will close their flowers on cold, dreary days. What is so special about the Arctic gentian is that it seems especially attuned to the weather. Within minutes of an incoming thunderstorm (a daily occurrence in the Rockies, for example) the Arctic gentian will close up its flowers. This is done via changes in turgor pressure within the cells. But what is the signal that cues this gentian in that a storm is fast approaching?

Researchers have investigated multiple stimuli in search of the answer. Plants don't seem to respond to changes in sunlight, wind, or humidity. Instead, temperature seemed to be the only signal capable of eliciting this response. When temperatures suddenly drop, the flowers will begin to close. Only when the temperature begins to rise will the flowers reopen. These movements are quite rapid too. Flowers will close completely within 6 - 10 minutes of a rapid decease in temperature. The reverse takes a bit longer, with most flowers needing 25 - 40 minutes to reopen.

So, why does the plant go through the trouble of closing up shop? It all has to do with sexual reproduction in these harsh conditions. Because this species doesn't self, pollen is at a premium. The plant simply can't afford the risk of rain washing it all away. The tightly closed flowers prevent that from happening. Also, wet flowers have been shown to discourage pollinators, even when favorable weather returns. Aside from interfering with pollen, rain also dilutes nectar, reducing its energy content and thus reducing the reward for any bee that would potentially visit the flower.

Being able to rapidly respond in changes in weather is important in these volatile habitats. Plants must be able to cope otherwise they risk extirpation. By closing up its flowers during inclement weather, the Arctic gentian is able to protect its vital reproductive resources.

Photo Credits: [1]

Further Reading: [1]


Meet The Compass Plant

Few prairie plants stand out more than the compass plant (Silphium laciniatum). With its uniquely lobed leaves and a flower stalk that rises well above the rest of the vegetation, it is nearly impossible to miss. It is also quite easy to identify. Seeing a population in full bloom is truly a sight to behold but the ecology of this species makes appreciating its splendor all the more enjoyable. Today I would like to introduce you to this wonderful member of the aster family.

Any discussion about this species inevitably turns to its common name. Why compass plant? It all has to do with those lovely lobed leaves. When they first develop, the leaves of the compass plant are arranged randomly. However, within 2 to 3 weeks, the leaves will orient themselves so that their flat surfaces face east and west. They also stand vertically. This is such a reliable feature of the plant that past generations have learned to use it as a reliable way in which to orient themselves.

Of course, helping humans find their way is not why this feature evolved. The answer to their orientation has to do with surviving in the open habitats in which they grow. Anyone who has ever spent time hiking around in prairie-like habitats will tell you that the sun can be punishing and temperatures get hot. What's more, the range of this species overlaps with much of the rain shadow produced by the Rocky Mountains meaning water can often be in short supply.

By orienting their leaves in a vertical position with the flat surfaces face east and west, the plants are able to maximize their carbon gain as well as their water use efficiency. At the same time, the vertical orientation limits the amount of direct solar radiation hitting the leaf. In essence, compass plant leaf orientation has evolved in response to the stresses of their environment. Research has shown that the sun's position in early morning is the stimulus that the plant cues in on during leaf growth.

Aside from its fascinating biology, the compass plant is also ecologically important. Myriad pollinators visit its large composite flowers and many different species of birds feed on their seeds. However, it is the insect community supported by the compass plant that is most impressive. Surveys have shown that nearly 80 different species of insect can be found living on or in it stems. Many of these are gall making wasps and their respective parasitoids. With individual plants producing up to 12 stems each, these numbers soon become overwhelming. Needless to say, this is one of the cornerstone plant species anywhere it grows naturally.

Photo Credit: [1]

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


An Orchid of Hybrid Origin

Hybridization is an often overlooked mechanism for evolution. We are taught in high school that hybrids such as mules and ligers are one-off's, evolutionary dead ends doomed to a life of sterility. Certainly this holds true in many instances. Species separated by great lengths of time and space are simply incompatible. However, there are instances throughout the various kingdoms of life in which hybrids do turn out viable.

If they are different enough from either parent, their creation may lead to speciation down the line. Such events have been found in ferns, butterflies, and even birds. One particular example of a hybrid species only recently came to my attention. While touring the Atlanta Botanical Garden I came across a fenced off bed of plants. Inside the fence were orchids standing about knee height. At the top of each plant was a brilliant spike of orange flowers. "Ah," I exclaimed, "the orange fringed orchid!" The reply I got was unexpected - "Sort of."

What I had stumbled across was neither the orange fringed orchid (Platanthera ciliaris) nor the crested yellow orchid (Platanthera cristata). What I was looking at were a small handful of the globally imperiled Chapman's fringed orchid (Platanthera chapmanii). Though there is some debate about the origins of this species, many believe it to be a naturally occurring hybrid of the other two. In many ways it is a perfect intermediate. Despite its possible hybrid origins, it nonetheless produces viable seed. What's more, it readily hybridizes with both parental species as well as a handful of other Platanthera with which it sometimes shares habitat.

Despite occasionally being found along wet roadside ditches, this species is rapidly losing ground. The wet meadows and pine savannas it prefers are all too quickly being leveled for housing and other forms of development. Although it once ranged from southeast Texas to northern Florida, and southeast Georgia, it has since been reduced to less than 1000 individuals scattered among these three states.

There is a light at the end of the tunnel though. Many efforts are being put forth to protect and conserve this lovely orchid. Greenhouse propagation in places like the Atlanta Botanical Garden are helping supplement wild populations while at the same time, maintaining genetic diversity. New populations have been located in Georgia and are now under protection. Though not out of the woods yet, this species serves as a reminder that a little bit of effort can go a long way.

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

How Plants Perceive Light

For all but a handful of plants, sunlight is vital to their existence. It provides the energy needed to break molecules of CO2 and water in order to synthesize carbohydrates. It is no wonder then that plants are incredibly attuned to their light environment. They grow towards it, they compete for it, they simply can't live without it. Exactly how plants (as well as many bacteria and even some fungi) perceive light is quite fascinating. It involves a small family of proteins called "phytochromes" whose chemical properties function like an on and off switch. Today I would like to briefly introduce you to this system. 

The activity of phytochrome proteins can be quite complex. In fact, many aspects of this system are still awaiting discovery. Still, we know pretty well how the phytochrome system functions with light and it all comes down to the color red. Pure sunlight is white light. It contains all of the wavelengths in the visible spectrum and then some. Phytochrome responds to two areas of this spectrum: red wavelengths of around 667 nm and far-red wavelengths around 730 nm. 

This range of the spectrum is quite useful when it comes to assessing whether or not there is enough light for photosynthesis. Unfiltered sunlight contains the most red light. As sunlight passes through the leaves of the canopy or as the sun sets, the ratio of far-red light increases. Far-red light is not conducive to photosynthesis. As such, the long-term survival of photosynthetic organisms is tied to figuring out the relative abundance of red and far-red light. 

This is where the phytochrome system comes in. It comes in two forms - an active form and an inactive form. When the inactive form absorbs red wavelengths, it is converted to its active form. This is the form that signals to the plant that there is enough light for physiological activity. When the ratio of wavelengths hitting the active form becomes dominated by far-red wavelengths (as it does when a plant is shaded or when the sun sets), the phytochrome is converted back into its inactive form. This in turn signals the plant to shut down many of the physiological activities within.

The structure of phytochrome in its inactive form (left) and active form (right).

The structure of phytochrome in its inactive form (left) and active form (right).

This on and off switch is how plants regulate everything from growth to flowering. The ratio of active to inactive forms can tell some plants what time of year it is. If there is more inactive form within its tissues, the plant "knows" that the days are growing shorter. Phytochrome is also involved in the number and the size of leaves that a plant will produce. Similarly, it is how plants know when they are being shaded out by their neighbors. The more neighboring plants there are, the more filtered the sunlight becomes and the ratio of far-red light increases. It is even involved in the process of seed germination. Small seeds that don't have enough food reserves (think lettuce seeds) will only germinate once their phytochrome is converted to its active form. In doing so, they ensure that they aren't germinating in an environment with too much shade or deep under the soil. 

Scientists are still working out exactly how the phytochrome system is able to regulate so many functions in plants. In some cases it can directly interact with molecules in the cytoplasm of plant cells. In other cases, it is transported into the nucleus where it can activate or deactivate particular genes. What we do know is that the phytochrome system is vitally important not just for the organisms that produce it, but for life as we know it. Without plants there could be no life on this planet.

Photo Credits: [1] [2]

Further Reading: [1] [2] [3] [4]

The Flowering Rush

Say the words "flowering rush" and many will picture some grass-like, pond vegetation. However, the plant I am talking about today is not a rush at all. Known scientifically as Butomus umbellatus, the flowering rush superficially resembles a patch of true rushes, especially when not in flower. However, it is actually quite a unique species and the sole member of the family Butomaceae. Native to parts of Europe and Asia, this beautiful aquatic plant can now be found invading wetlands throughout northern North America.

Growing quite tall and producing an umbel of beautiful pink flowers, it is no wonder that this plant came to North America as a horticultural curiosity. Its overall appearance suggests a relationship with the genus Allium but genetic analysis puts it somewhere near the water plantains - Alismataceae. The interesting thing about this plant is that here in North America, individual populations exhibit either diploid or triploid chromosome counts.

This is most likely a function of its horticultural past. Many commonly grown garden species have been selected for polyploidy in their chromosomes. Polyploid plants are often larger and more hardy than their diploid relatives, mostly due to the extra genetic material they harbor. It has been noted that there seems to be some reproductive differences between diploid and triploid flowering rush populations as a result. Diploids are more likely to reproduce sexually via seeds whereas triploids are usually sterile and reproduce vegetatively. Triploids are also less commonly found as escapees but they are more widely distributed than diploids. This is likely due to the fact that triploids are more commonly planted in gardens.

Whereas it seems that there is plenty of areas where people disagree on the invasive species issue, one thing we must keep in mind is that, no matter where you stand, biological invasions are one of the largest natural experiments this world has ever seen. We mustn't waste any opportunity to learn from these invasions and to gather as much data as we possibly can. Species like flowering rush offer us insights into how and why some species become invasive while others do not. The more we know, the better we can learn from the mistakes of the past.

Photo Credit: [1] [2]

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

The Stinging Nettles

We've all been there at some point. It's summer, it's a beautiful day, and you find yourself strolling along a trail. You are walking along, enjoying the sights, sounds, and smells of your environment when you harmlessly brush by a patch of waist-high plants. You don't think anything of it. They are herbaceous and don't readily catch the eye. A few steps later and the burning starts. It is mild at first but wherever your skin met the tissues of those plants an itchy, burning sensation starts to amplify. You have likely just encountered a species of stinging nettle. 

Nettles hail from a handful of genera. There are many different species of nettle but you are most likely to encounter either stinging nettle (Urtica dioica) or the wood nettle (Laportea canadensis), all of which belong to the nettle family (Urticaceae). A closer inspection of the plant reveals that the stems as well as the underside of the leaves are covered in tiny hairs. These hairs are called trichomes. A subset of these trichomes are what caused your discomfort. 

Anatomy of a stinging trichome

Anatomy of a stinging trichome

These trichomes have been honed by natural selection into a very effective defense. They are an elongated cell that sits atop of a multicellular pedestal. They are quite brittle and any contact with them causes their tips to break. They are also hollow and once they are broken, they essentially function like mini hypodermic needles. They penetrate the skin of any animal unlucky enough to brush up against them and inject an irritating fluid into the tissues of their "attacker." The fluid itself is quite interesting. Chemical analyses have revealed that it consists of a complex mixture of histamines, acetylcholine, serotonin, and even formic acid. Chemists are still working out the exact makeup of this chemical weapon and how much variation there is between different stinging species. 

As you might have deduced by this point, these stinging hairs are a defense mechanism. They protect the plant from herbivores. However, not all herbivores are deterred by this defense. It was found that invertebrates don't seem to have any issue navigating the stinging hairs. Instead, it is thought that the stinging nature of these plants evolved in response to large mammalian herbivores. This makes some sense as larger herbivores pose more of a threat to the entire plant than do invertebrates.

Stinging nettle (Urtica dioica) 

Stinging nettle (Urtica dioica

Even more interesting is the response of some nettles to varying levels of herbivory. It has been found that heavily damaged plants will regrow leaves and stems with higher densities of stinging hairs than those of plants that have experienced lower rates of herbivory. This too makes a lot of sense. Stinging hairs require resources to produce so plants that have not experienced high rates of herbivory do not bother allocating precious resources to their production.

Even more interesting is the fact that for stinging nettle (U. dioica), male and female plants tend to have differing densities of stinging hairs. Female plants produce more stinging hairs than males. It is thought that since females must invest more resources into producing seeds than males do into producing pollen, they must also invest in more protection for these valuable reproductive assets. 

These nettles are not alone in producing such stinging trichomes. Many other plant species have converged on this defensive strategy. If you have ever experienced this for yourself, you can really understand just how effective it can be. 

Wood nettle (Laportea canadensis)

Wood nettle (Laportea canadensis)

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

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

Got Herbivores? Turn Them Into Cannibals!

Plants have to deal with quite a lot in their day to day lives. They can't get up and move like animals can. Due to their sessile nature, plants rely on a suite of physical and chemical traits for defense. The world of plant chemistry is quite amazing and thanks to new research published in Nature Ecology & Evolution, it has gotten even more interesting. Under attack by herbivorous insects, some plant species are able to turn their vegetarian predators into cannibals. 

Cannibalism in insects is not unheard of, even among the herbivorous species. When the going gets tough, why not eat your sibling or your neighbor? Well, research using tomatoes and the army beetworm (Spodoptera exigua) suggests that plants might be able to induce this behavior in caterpillars long before it would happen naturally. It makes sense too. Plants that are able to induce cannibalistic behavior via chemical means not only reduce grazing pressures on their own tissues, they also reduce the number of herbivores in the system.

The chemical in question here is called methyl jasmonate. It is a volatile organic compound produced by a plethora of plant species and is thought to play in role in a diverse array of biological functions such as germination, root growth, fruit ripening, and defense. It is often released when a plant becomes damaged. Neighboring plants are able to pick up on this compound and will begin to beef up their own defenses in response. After all, if your neighbor is being attacked, there is a decent chance you will be too. 

Researchers investigating the effects of this chemical on the beetworm (a common aggricultural pest) found that plants that were treated with methyl jasmonate induced beetworms to turn on one another through cannibalism. Caterpillars hanging out on plants that were not treated with methyl jasmonate only turned to cannibalism after they had consumed all of the leaves available, if at all. 

The researchers are now gearing up to figure out whether inducing cannibalism also helps to spread disease among caterpillars. This exciting new form of plant defenses opens up doors to many new questions and potentially safer forms of pest control. Considering the near ubiquity of methyl jasmonate in the botanical world, it begs the question as to how common this form of defense really is. 

Photo Credits: [1] [2] 

Further Reading: [1] [2]

Meet The Powder Gun Moss

I get very excited when I am able to identify a new moss. This is mainly due to the fact that moss ID is one of my weakest points. I was sitting down on a rock the other day taking a break from vegetation surveys when I looked to my right and saw something peculiar. The area was pretty sloped and there was some exposed soil in the vicinity. Covering some of that soil was what looked like green fuzz. Embedded in that fuzz were these strange green urns.

I busted out my hand lens and got a closer look. This was definitely a moss but one I had never seen before. The urns turned out to be capsules. Later, a bit of searching revealed this to be a species of moss in the genus Diphyscium. This genus is the largest within the family Diphysciaceae and here in North America, we have two representatives - D. foliosum and D. mucronifolium.

These peculiar mosses have earned themselves the common name 'powder gun moss.' The reason for this lies in those strange sessile capsules. Unlike other mosses that send their capsules up on long, hair-like seta in order to disperse their spores on the faintest of breezes, the Diphyscium capsules remain close to the ground. In lieu of wind, a powder gun moss uses rain. In much the same way puffball mushrooms harness the pounding of raindrops, so too do the capsules of the powder gun moss. Each raindrop that hits a capsule releases a cloud of spores that are ejected into an already humid environment full of germination potential.

Luckily for moss lovers like myself, the two species of Diphyscium here in North America tend to enjoy very different habitats. This makes a positive ID much more likely. D. foliosum prefers to grow on bare soils whereas D. mucronifolium prefers humid rock surfaces. Because of this distinction, I am quite certain the species I encountered is D. foliosum. And what a pleasant encounter it was. Like I said, it isn't often I accurately ID a moss so this genus now holds a special place in my mind.

Further Reading: [1] [2]


Plant Architecture and Its Evolutionary Implications

I make it a point that during my field season I enjoy my breakfast out on the deck. It is situated about halfway up the canopy of the surrounding forest and offers a unique perspective that is hard to come by elsewhere. Instead of looking up at the trees, I am situated in a way that allows for a better understanding of the overall structure of the forest. Its this perspective that generates a lot of different questions about what it takes to survive in a forested system, especially as it relates to sessile organisms like plants.

Quite possibly my favorite plants to observe from the deck are the pagoda dogwoods (Cornus alternifolia). As this common name suggests, this wonderful small tree takes on a pagoda-like growth form with its stacked, horizontal branching pattern. It is unmistakable against the backdrop of other small trees and shrubs in the mid canopy. The fact that it, as well as many other plant species, can be readily recognized and identified on shape alone will not be lost on most plant enthusiasts.

The fact that diagrams like these exist in tree guides is proof of the utility of this concept.

The fact that diagrams like these exist in tree guides is proof of the utility of this concept.

Even without the proper vocabulary to describe their forms, anyone with a keen search image understands there is a gestalt to most species and that there is more to this than simply fodder for dichotomous keys. The overall form of plants has garnered attention from a variety of fields. Such investigations involve fields of study like theoretical and quantitative biology to engineering and biomechanics. It has even been used to understand how life may evolve on other planets. It is a fascinating field of investigation and one worth a deeper look. 

Some of the pioneering work on this subject started with two European botanists: Dr. Francis Hallé and Dr. Roelof Oldeman. Together they worked on conceptual models of tree architecture. Using a plethora of empirical studies on whether a tree branches or doesn't, where branches occurs, how shoots extend, how branches differentiate, and whether reproductive structures are terminal or lateral, they were able to reduce the total number of tree forms down to 23 basic architectural models (pictured above). Each model describes the overall pattern with which plants grow, branch, and produce reproductive structures. At the core of these models is the concept of reiteration or the repitition of form in repeatable sub-units. The models themselves were given neutral names that reflect the botanists that provided the groundwork necessary to understand them.  

Despite the fact that these models are based on investigations of tropical tree species, they are largely applicable to all plant types whether they are woody or herbaceous and whether they occur in the temperate zone or in the tropics. The models themselves do not represent precise categories but rather points on a spectrum of architectural possibilities. Some plants may be intermediate between two forms or share features of more than one model. It should also be noted that most trees conform to a specific model for only a limited time period during their early years of development. After some time, random or stochastic events throughout a trees life greatly influence its overall structure. The authors are careful to point out that a trees crown is the result of all the deterministic, opportunistic, and chance events in its lifetime.  

Despite these exceptions, the adherence of most plants to these 23 basic models is quite remarkable. Although many of the 23 models are only found in the tropics (likely an artifact of the higher number of species in the tropics than in the temperate zones), they provide accurate reference points for further study. For instance, the restriction of some growth forms to the tropics raises intriguing questions. What is it about tropical habitats that restricts models such as Nozeran's (represented by chocolate - Theobroma cacao) and Aubréville's (represented by the sea almond - Terminalia catappa) to these tropical environments? It likely has to do with the way in which lateral buds develop. In these models, buds develop without a dormancy stage, a characteristic that is not possible in the seasonal climates of the temperate zones. 

Reiteration is an important process in plant architectural development in which plants repeat their basic model. This is especially important in repairing damage. 

Another interesting finding borne from these models is that there doesn't seem to be strong correlations between architecture and phylogeny. Although species within a specific genus often share similar architecture, there are often many exceptions. What's more, the same form can occur in unrelated species. For instance, Aubréville's model occurs in at least 19 different families. Similarly, the family Icacinaceae, which contains somewhere between 300 and 400 species, exhibits at least 7 of the different models. Alternatively, some families are architecturally quite simple. For instance the gymnosperms are considered architecturally poor, exhibiting only 4 of the different models. Even large families of flowering plants can be architecturally simplistic. The Fabaceae, for instance, are largely made up of plants exhibiting Troll's model. 

So, at this point the question of what is governing these models becomes apparent. If most plants can be reduced to these growth forms at some point in their life then there must be some aspect of the physical world that has shaped their evolution through time. Additionally, how does plant architecture at the physical level scale up to the level of a forest? Questions such as this are fundamental to our understanding of not only plants as organisms, but the role they play in shaping the world around us. 

Although many scientists have attempted to tackle these sorts of questions, I want to highlight the work on one individual in particular - Dr. Karl Niklas. His work utilizes mathematics to explain plant growth and form in relation to four basic physical constraints:

1) Plants have to capture sunlight and avoid shading their own leaves.

2) Plants have to support themselves structurally.

3) Plants have to conduct water to their various tissues.

4) Plants must be able to reproduce effectively.

Using these basic constraints, Dr. Niklas built a mathematical simulation of plant evolution. His model starts out as a "universe" containing billions of possible plant architectures. The model then assesses each of these forms on how well it is able to grow, survive, and reproduce through time. The model is then allowed to change environmental conditions to assess how these various forms perform as well as how they evolve. 

An example of Niklas' model showing how simple branching pattern (bottom) can evolve over time into more complex, yet familiar, forms (top).

An example of Niklas' model showing how simple branching pattern (bottom) can evolve over time into more complex, yet familiar, forms (top).

The most remarkable part of this model is that it inevitably produces all sorts of familiar plant forms, such as those we see in lycophytes, ferns, as well as many of the tree architectural models mentioned above. What's more, later iterations of the model as well as others do an amazingly accurate job at predicting forest structure dynamics such as self-thinning, mortality, and realistic size/frequency distributions of various species. 

It would appear that the rules governing what we know as a plant are to some degree universal. Because constraints such as light capture and the passive movement of water are firmly grounded in the laws of physics, it makes sense that the successful plant architectures we know and love today (as well as those present through the long history of plant evolution on this planet) are in large part a result of these physical constraints. It also begs the question of what photosynthetic life would look like on other planets. It is likely that if life arose and made its living in a similar way, familiar "plant" architecture could very well exist on other planets.

Photo Credits: [1] [2] [3]

Further Reading: [1] [2] [3] [4] [5]

Meet Jones' Columbine

Meet Aquilegia jonesii. This interesting little columbine can be found growing in a narrow range along the northern Rockies. It only grows in alpine and sub-alpine zones, making it quite rare. It has a cushion-like growth form to shield it from the elements but disproportionately large flowers. It is a lucky day if one stumbles across this species! 

Fun Fact: Both the common name and generic name of the flowers referred to collectively as "columbines" have their origins in ornithology? 

That's right, the genus to which they belong, Aquilegia, can trace its origin to the word "aquila," which is Latin for "eagle." When the genus was being described, it was felt that the flower resembled the claw of an eagle. 

The word "columbine" has it's origins in the word "columba," which is Latin for "pigeon" or "dove." Early botanical enthusiasts felt that the nectar spurs resembled the heads of a group of doves. 

More and more I am coming on board with the idea that etymology can be quite fun.

Photo Credit: Steve (http://bit.ly/NbGbmz)

Further Reading: [1] [2] [3]

North America's Native Bamboos

I would like to introduce you to North America's native bamboos. There are three species, all hailing from the same genus - Arundinaria. Today they hardly get the attention they deserve but in the past, there were an incredibly important group of plants both ecologically and culturally. Today they occupy a mere shadow of this former glory so in keeping with the goal of In Defense of Plants, I am here to defend these plants. 

There are three species in the genus Arundinaria -- A. appalachiana, A. gigantea, and A. tecta -- and all of these are native to the southeast. There has been a whole lot of taxonomic debate over these plants ever since Thomas Walter first described the first of them in 1788. Since then, there have been many revisions. Whether or not any Asian bamboos belong in this genus is a story for another time but recent genetic work confirms that these three species are valid. 

Each differs slightly in its ecology. Giant or river cane (A. gigantea) is a denizen of alluvial forests and swamps as is switch cane (A. tecta), although switch cane seems to be a bit more obligate in its need for swamp-like habitats. Hill cane (A. appalachiana) was only described in 2006 and prefers dry to moist forested slopes and forest edges. One interesting things about hill cane is that it drops its leaves in the fall, an unusual trait for a bamboo. 

A majority of their reproduction is asexual via spreading rhizomes. All three species of cane rarely flower. When they do, plants usually die after setting seed. As such, a majority of canes you may encounter in the wild are clones connected by a vast network of large rhizomes. These rhizomes can persist for decades or even centuries meaning persistent patches are quite old. These rhizomes can lay dormant for some time as well, waiting for some form of canopy clearing disturbance to provide the conditions they need to grow again. 

Despite how common these canes may seem in some areas, they are nowhere near what they once were. European settlers wrote of vast stretches of rivers and swamps completely covered in cane. They called these "canebrakes" and they persisted as such due to the importance of Arundinaria to Native Americans. Regular burning created perfect conditions for cane to thrive and thrive it did. 

Because it was once so prolific, its ecological impacts were quite immense. Many animals relied on canebrakes for food, shelter, and a place to breed. Unfortunately, cane was also highly sought after as food for cattle. Unsustainable grazing took its toll, as did fire suppression. What's more, the rich soils and relatively flat topography in which these canes tend to grow was also the preferred spot for farming. In fact, settlers used canebrakes as an indicator of good soils. Vast acres of cane were cleared and plowed under. Unfortunately for cane and the habitat it created, when it disappeared, so did much of its function.

Once cleared, cane is slow to return. Its tendency to not flower frequently means few seeds are ever produced. Even clonal reproduction can be tedious if the right conditions are not present. Cane has lost most of the ground in which it once grew. With it went vital components of the southeastern ecosystem. It has even been suggested that the loss of canebrakes played a major role in the extinction of Bachman's warbler (Vermivora bachmanii) though it is hard to say for sure. 

Though all three species of cane still persist today, they are not the ecosystem builders they once were. It will take a lot of changes here in North America both ecologically and culturally before these three bamboos can ever regain much of their former range. Still, they are interesting plants to encounter and well worth taking some time to enjoy. 

Photo Credits: [1] [2]

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

Eastern North America's Temperate Rainforest

I have often remarked that working in the southern Appalachian Mountains during the summer feels more like working in a rainforest than it does an eastern deciduous forest. Lots of rain, high humidity, and a bewildering array of flora and fauna conjure up images of some far away jungle. Only winter can snap this view out of ones head. I recently learned, however, that these feelings are not misplaced. Indeed, this region of southern Appalachia is considered a temperate rainforest. 

These mountains are old. They arose some 480 million years ago and have been shaping life in this region of North America ever since. Another thing these mountains are quite good at is creating their own weather systems. Here in southern Appalachia, warm, wet air from the Gulf of Mexico and western Atlantic blows northward until it hits the Appalachian Mountains. The mountainous terrain comprising parts of Pisgah, Nantahala, and Chattahoochee National Forests has been referred to as "the Blue Wall" and is responsible for the unique conditions that created this temperate rainforest.

As this air rises over their peaks, it begins to cool. As it does, water in the air condenses. This results in torrents of rain. On average, this area receives anywhere from 60 to 100+ inches of rain every year. The Appalachian temperate rainforest is second only to the Pacific Northwest in terms of rainfall in North America. All of this water and heat coupled with the age and relative stability of this ecosystem over time has led to the explosion of biodiversity we know and love today. 

Life abounds in the southern Apps. The plant diversity can be rather intimidating as species from the north mix with those coming up from the south. For instance, there are more tree species in these mountains than in all of Europe.  Rates of endemism in these mountains, both in terms of flora and fauna, are remarkable. There are relics of bygone eras that never expanded their range following repeated glaciations. What's more, a multitude of species combinations can be found as you go from low to high elevations. 

At lower elevation, forests are dominated by American beech (Fagus grandifolia), yellow birch (Betula alleghaniensis), maple (Acer spp.), birch (Betula spp.), and oak (Quercus spp.). Magnolias cover the humid coves. Mid elevations boast birches, mountain ash (Sorbus americana), and mountain maple (Acer spicatum). High elevations contain fraser fir (Abies fraseri) and redspruce (Picea rubens). Both the understory and the the mountain balds are home to a staggering array of different Heaths (Ericaceae). From Rhododendrons to azaleas and mountain laurels, the colors are like those lifted from an abstract painting. The forest floor is where I focus most of my energy. It is hard to capture the diversity of this habitat in only a few paragraphs. What I can say is that I haven't even scratched the surface. It seems like there is something new to see around every corner. 

The point I am trying to make is that this region is quite special. It is something worth protecting. From development to mining and changes in temperature and precipitation, human activities are exacting quite a toll on the Appalachian Mountains. The system is changing and there is no telling what the future is going to look like. Conserving wild places is a must. There is no way around it. Luckily there is a reason people love this place so very much. There are a lot of dedicated folks out there working to protect and conserve everything that makes southern Appalachia what it is. Get out there, enjoy, and support your local land trust!

Further Reading:  [1] 

The Sterile Flowers of Hydrangea

Flowers are essentially billboards. They are saying to potential pollinators "hey, I'm full of energy-rich food and totally worth visiting." However, flowers are costly to produce and maintain. Reproduction isn't cheap, which has led some plants to take a more cost effective rout. In the genus Hydrangea, this means producing large, showy sterile flowers that draw attention to their smaller, less gaudy fertile flowers. 

These sterile flowers are technically colored up sepals. They don't produce reproductive structures or pollen. They are simply calling cards to insects that food is nearby. In the wild, Hydrangeas produce relatively few of these sterile flowers. Apparently it doesn't take much to draw insects in. The horticultural trade has shifted this balance to an obscene degree. When you look at a cultivated Hydrangea with its giant pom-pom looking corymb you are looking at a sterile structure that offers little if anything for pollinators. 


This is a shame really because wild Hydrangeas are quite a boon for insects. Everything from beetles to bees visit their flowers. From the moment they open until the last one is fertilized, these shrubs are buzzing with activity. If you have the choice of a native Hydrangea over a cultivar, consider planting the native instead. You and you local pollinators will be happy you did. Here in North America there are at least four to choose from - the smooth Hydrangea (Hydrangea arborescens), the ashy Hydrangea (Hydrangea cinerea), the oakleaf Hydrangea (Hydrangea quercifolia), and the silverleaf Hydrangea (Hydrangea radiata). All of these occur east of the Mississippi and are largely denizens of the southeast. 

Further Reading: [1]

The White Walnut

I must admit, I am not very savvy when it comes to trees. I love and appreciate them all the same, however, my attention is often paid to the species growing beneath their canopy. last summer changed a lot of that. I was very lucky to be surrounded by people that know trees quite well. Needless to say I picked up a lot of great skills from them. Despite all of this new information knocking around in my brain, there was one tree that seemed to stand out from the rest and that species is Juglans cinerea.

Afternoons and evenings at the research station were a time for sharing. We would all come out of the field each day tired but excited. The days finds were recounted to eager ears. Often these stories segued into our goals for the coming days. That is how I first heard of the elusive "white walnut." I had to admit, it sounded made up. Its as if I was being told a folktale of a tree that lived in the imagination of anyone who spent too much time in the forest. 

Only a handful of people knew what it was. I listened intently for a bit, hoping to pick up some sort of clue as to what exactly this tree was. Finally I couldn't take it any longer so I chimed in and asked. As it turns out, the white walnut is a tree I was already familiar with, though not personally. Another common name for this mysterious tree is the butternut. Ah, common names. 

I instantly recalled a memory from a few years back. A friend of mine was quite excited about finding a handful of these trees. He was very hesitant to reveal the location but as proof of his discovery he produced a handful of nuts that sort of resembled those of a black walnut. These nuts were more egg shaped and not nearly as large. Refocusing on the conversation at hand, I now had a new set of questions. Why was this tree so special? Moreover, why was it so hard to find?

The white walnut has quite a large distribution in relation to all the excitement. Preferring to grow along stream banks in well-drained soils, this tree is native from New Brunswick to northern Arkansas. Its leaflets are downy, its bark is light gray to almost silver, and it has a band of fuzzy hairs along the upper margins of the leaf scars. Its a stunning tree to say the least. 

Sadly, it is a species in decline. As it turns out, the excitement surrounding this tree is due to the fact that finding large, robust adults has become a somewhat rare occurrence. Yet another casualty of the global movement of species from continent to continent, the white walnut is falling victim to an invasive species of fungus known scientifically as Sirococcus clavigignenti-juglandacearum

The fungus enters the tree through wounds in the bark and, through a complex life cycle, causes cankers to form. These cankers open the tree up to subsequent infections and eventually girdle it. The fungus was first discovered in Wisconsin but has now spread throughout the entire range of the tree. The losses in Wisconsin alone are staggering with an estimated 90% infection rate. Farther south in the white walnuts range, it is even worse. Some believe it is only a matter of time before white walnut becomes functionally extinct in areas such as the Carolinas. No one knows for sure where this fungus came from but Asia is a likely candidate.

A sad and all too common story to say the least. It was starting to look like I was not going to get a chance to meet this tree in person... ever. My luck changed a few weeks later. My friend Mark took us on a walk near a creek and forced us to keep our eyes on the canopy. We walked under a tree and he made sure to point out some compound leaves. With sunlight pouring through the canopy we were able to make out a set of leaves with a subtle haze around the leaf margins. We followed the leaves to the branches and down to the trunk. It was silvery. There we were standing under a large, healthy white walnut. The next day we stumbled across a few young saplings in some of our vegetation plots. All is not lost. I can't speak for the future of this species but I feel very lucky to have seen some healthy individuals. With a little bit of luck there may be hope of resistance to this deadly fungus. Only time will tell. 

Photo Credit: Dan Mullen (http://bit.ly/2br2F0Z)

Further Reading: