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. 

IMG_1914.jpg

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:
http://bit.ly/2b8GiMV

http://bit.ly/2aLUdMD

Pitcher's Thistle and the Dunes It Calls Home

Sand dunes are harsh habitats for any organism to make a living. They are hot, they are low in nutrients, water doesn't stick around for very long, and they can be incredibly unstable. Despite these obstacles, dunes around the world host rather unique floras comprised of plants well suited to these conditions. Sadly, we humans have been pretty good at destroying many of these dune habitats. This is especially true along the shores of the Great Lakes. To put this in perspective, I would like us to take a closer look at a special Great Lakes dune denizen. 

Meet Pitcher's thistle (Cirsium pitcheri). It is a true dune plant and is endemic to the shores of the upper Great Lakes. Its a rather lanky plant, often looking as if it is having a hard time supporting its own weight. Despite its unkempt look, adult plants can reach heights of 3 feet, which is quite impressive given where it lives. It is covered in silvery hairs, giving the plant a shiny appearance. These hairs likely protect the plant from the onslaught of sun, abrasive wind-blown sand, and desiccation. One of the benefits of growing in such inhospitable places is that historically speaking, Pitcher's thistle could grow with little competition. Individual plants grow for roughly 5 to 8 years before flowering. After seeds are produced, the plant dies. The seedlings are then free to develop without being shaded out. 

The last century or so have not been good to Pitcher's thistle. Shoreline development, altered disturbance regimes, and isolation of various populations have fragmented its range and reduced its genetic diversity. To make matters worse, its remaining habitat is still shrinking. Shoreline development has altered wave action that is vital to these dune habitats. Waves that once brought in new sediments and built dunes are largely carving away what's left. They are eroding at an alarming rate that even dune-adapted plants like Pitcher's thistle can't keep up with. Recreational use of these habitats adds another layer as heavy foot traffic carves deep scars into these dunes, furthering their demise. 

One silver lining in all of this is that dedicated researchers are paying close attention to the natural history of this species. They have discovered some fascinating things that will help in the recovery of this special plant. For instance, it has been observed that although trampling doesn't necessarily kill Pitcher's thistle, it does damage sensitive buds. This often results in plants developing multiple flower heads. Although this sounds like a benefit, researchers discovered that these damaged plants actually produce fewer viable seeds despite producing more flowers. 

Also, they have found that American goldfinches are playing a considerable role in its reproductive success. Despite the tightly clasping, spiny bracts that protect the seeds, goldfinches have been found to reduce seed production by 90% as they forage for food and the fluffy seed hairs for nest building. Evidence suggests that goldfinches are more likely to target small, isolated populations of Pitcher's thistle rather than large, contiguous patches. The reason for this is anyone's guess but it does suggest that they way around this issue is to supplement dwindling populations with new plants grown from seed. 

Without intervention, it is very likely that Pitcher's thistle would go extinct in the near future. Luckily, researchers and federal officials are teaming up to make sure that doesn't happen. Long term population monitoring is in place throughout its range and a sandbox technique has been developed for germinating and growing up new individuals to supplement wild populations. Through habitat restoration efforts, supplementing of existing and the creation of new populations, the future of this charismatic dune thistle has gotten a little bit brighter. It isn't out of the metaphorical woods but there is reason for hope. 

Photo Credit: [1] 

Further Reading: [1]

A Unique Case of Floral Mimicry

Pollination is one of the major advantages flowering plants have over the rest of the botanical tree. With a few exceptions, flowers have cornered this market. It no doubt has played a significant role in their rise to dominance on the landscape. The importance of flowers is highlighted by the fact that they are costly structures. Because they don't photosynthesize, all plants take a hit on energy reserves when it comes time to flower. Sepals, petals, pollen, nectar, all of these take a lot of energy to produce which is why some plants cheat the system a bit. 

Sexual mimicry is one form of ruse that has evolved repeatedly. The flowers of such tricksters mimic receptive female insects waiting for a mate. The evolution of such a strategy taps into something far deeper in the mind of animals than food. It taps into the need to reproduce and that is one need animals don't readily forego. As such, sexually deceptive flowers usually do away with the production of costly substances such as nectar. They simply don't need it to attract their pollinators. 

By and large, the world of sexual mimicry in plants is one played out mainly by orchids. However, there exists an interesting exception to this rule. A daisy that goes by the scientific name Gorteria diffusa has evolved a sexually deceptive floral strategy of its own. Native to South Africa, this daisy is at home in its Mediterranean climate. It produces stunning orange flowers that very much look like those of a daisy. On certain petals of the ray florets, one will notice peculiar black spots. From region to region there seems to be a lot of variation in the expression of these spots but all are textured thanks to a complex of different cell types. 

The spots may seem like random patterns until the flowers are visited by their pollinator - a tiny bee-fly known scientifically as Megapalpus nitidus. With flies present, one can sort of see a resemblance. This would not be a mistake on the observers part. Indeed, when researchers removed or altered these spots, bee-fly visitation significantly decreased. Although this didn't seem to influence seed production, it nonetheless suggests that those spots are there for the flies. 

When researchers painted spots on to non-textured petals, the bee-flies ignored those as well. It appears that the texture of the spots makes a big difference to visiting flies. What's more, although female flies visited the flowers, a majority of the visits were by males. It appears that the presence of these spots is keying in on the mate-seeking and aggregation behavior of their bee-fly pollinators. Further investigation has revealed that the spots even reflect the same kind of UV light as the flies themselves, making the ruse all the more accurate. This case of sexual mimicry is unique among this family. No other member of the family Asteraceae exhibits such reproductive traits (that we know of). Although it doesn't seem like seed production is pollinator limited, it certainly increases the chance of cross pollination with unrelated individuals.

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

Further Reading: [1] [2]

Parasitic Protection

Strangler figs are remarkable organisms. Germinating in the canopy of another tree, their roots gradually wrap around the host, growing down towards to forest floor. Once in the soil, the interwoven structure of the fig begins to grow and swell. Over time, the strangler fig does what its name suggests, it strangles the host tree. Strangling is bad news for the host, however, new research suggests that strangler figs may actually provide some benefit to larger host trees, at least for part of its life. 

Cyclones are a force to be reckoned with. Their punishing winds can quickly topple even the sturdiest of trees. This is exactly what happened in 2013 when Cyclone Oswald struck Lamington National Park in Australia. Many trees fell victim to this storm but not all. Survival was not random and an interesting pattern started to emerge when researchers began surveying the damage. 

The hollow center of an ancient strangler fig where its host tree once grew and has long since rotted away.  

The hollow center of an ancient strangler fig where its host tree once grew and has long since rotted away.  

They found that large trees hosting strangler figs survived the storm whereas those without were more likely to be uprooted. It appears that hosting these parasitic figs just might have some benefits after all. There are a handful of mechanisms with which strangler figs could be helping their hosts. First is that figs spanning multiple trees may provide stability for the host and its neighbors. Another could come in the form of additional leaf area. The canopy of both the fig and its host tree may help reduce the impact of the cyclone winds. Additionally, once they make it to the soil, the roots of the strangler fig may act as guy-wires, keeping the host tree from uprooting. Finally, The interwoven roots of the strangler fig may act as scaffolding, providing additional structural integrity to the host tree. 

More work will be needed to see which of these are the most likely mechanisms. The mere fact that this parasitic relationship might not be so one-sided after all is quite interesting. What's more, by keeping large tree species alive through devastating cyclone events, the figs are essentially keeping legacy trees alive that can then reseed the surrounding forest. This could explain why host trees have not evolved any obvious mechanism to avoid strangler fig infestation. 

Further Reading: [1]

The Enemy of My Enemy is My Friend

Spotted Knapweed (Centaurea maculosa)

Spotted Knapweed (Centaurea maculosa)

Plants produce a lot of chemicals. I mean a lot. Some of these are involved in day to day functions like growth and reproduction. The function of others can be a bit less obvious. These are often referred to as secondary compounds as they are not directly involved in growth or reproduction. Some of these chemicals are toxic to other plants. We call these compounds allelochemicals. Producing allelochemicals can give some plants a competitive advantage by knocking back their neighbors. However, like most things in ecology, this situation isn't always that simple. 

Take the example of spotted knapweed (Centaurea maculosa). This nasty invader is wreaking havoc on plant communities throughout western North America. It wages its war under the soil where it releases a chemical from its roots called "catechin." This chemicla kills native plants, especially native grasses growing nearby. This competitive advantage can lead to total dominance of spotted knapweed in many areas where it quickly rises to monoculture status. 

Silky lupine (Lupinus sericeus)

Silky lupine (Lupinus sericeus)

Not all native plants are equally susceptible to spotted knapweeds effects. Two native forbs stand out above the rest in being able to cope with the allelochemicals released by spotted knapweed. Enter silky lupine (Lupinus sericeus) and blanketflower (Gaillardia grandiflora). Where these plants occur alongside spotted knapweed, other natives seem to do a bit better. This made researchers curious. What was it about these two species?

Blanketflower (Gaillardia grandiflora)

Blanketflower (Gaillardia grandiflora)

As it turns out, both of these natives secrete their own chemicals. These don't act as allelochemicals though. Instead, it was found that they neutralize the detrimental effects of the catechin. In doing so, both the lupine and the blanketflower create a safe zone for other natives to reestablish. This could be good news as it hints at new ways of approaching certain plant invasions. More work needs to be done to see how well this situation plays out in a natural setting but the evidence is tantilizing to say the least!

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

Further Reading: [1]

Who Pollinates the Flame Azalea?

By and large, one of the most endearing aspects of doing research in Southern Appalachia are the myriad Ericaceous species you inevitably encounter. Throughout the growing season, their flowers paint the mountainsides in a symphony of color. One of my favorite species to encounter is the flame azalea (Rhododendron calendulaceum).

This shrubby spectacle is a common occurrence where I work and its flowers, which range from bright yellows to deep orange and even red, put on a show that lasts a couple of weeks. It's not just me who enjoys the flowers either. Countless insects can be seen flitting to and from each blossom, sucking up rich reserves of nectar and pollen. It is interesting to watch a bee visit these flowers. Their outlandishly long anthers and style seem to be mostly out of reach for these smaller pollinators.

Bees attempting to grab some pollen look outlandishly clumsy in their attempts. What's more, small insects only seem to be able to get either nectar or pollen on any given visit. Rarely if ever do they make contact with the right floral parts that would result in effective pollination. Indeed, I am not the only person to have noticed this. Despite being visited by a wide array of insect species, only large butterflies seem capable to pollinating the flame azaleas stunning blooms.

The mechanism by which this happens is quite interesting. The reason small insects do not effectively pollinate these flowers has to do with the position of the anthers and style. Sticking far out from the center of the flower, they are too widely spaced to be contacted by small insect visitors. Instead, the only insects capable to transferring pollen from anthers to stigma are large butterflies. What is most strange about this relationship is that it all hinges on the size of the butterflies wings.

Only two species of butterfly, the eastern tiger swallowtail and the orange spangled fritillary, were observed to possess the right wing size and placement to achieve effective pollination for the flame azalea (though I suspect other larger species do so as well). This is quite unique as this is the only report of wing-mediated pollen transfer in northern temperate regions. The research team that discovered this noted that pollen transfer was greatest with the eastern tiger swallowtail, which is a voracious nectar hunter during the summer months.

Despite their popularity in pollinator gardens, butterflies are often considered poor pollinators. That being said, pollen transfer via wing surfaces has been a largely overlooked mechanism of pollination. Coupled with a handful of reports from tropical regions, this recent finding suggests that we must take a closer look at plant pollinator interactions, especially for plants that produce flowers with highly exerted anthers and stigmas. As the authors of the study put it, "transfer of pollen by butterfly wings may not be a rare event."

Photo Credit: [1]

Further Reading: [1]

Taxonomic Discoveries: My Version of the Butterfly Effect

Witnessing a giant swallowtail (Papilio cresphontes) in flight is an incredible experience. It is the largest species of butterfly found in the US and Canada and with its yellow and black wings, it is impossible not to take pause and watch it flutter around the canopy. I will never forget the first time I saw one as a child. It was one of those moments that solidified my obsession with the natural world. Fast forward a few decades and now I can't help but ponder what kind of gardening I would need to do to attract these incredible insects to my yard. What I discovered surprised me to say the least. I had to plant something in the citrus family. 

We are all familiar with the fruits of various Rutaceae. This family contains the genus Citrus, providing humanity with oranges (C. × sinensis), lemons (C. × limon), grapefruits (C. × paradisi), and limes (mostly C. aurantifolia). These are largely tropical and subtropical trees, struggling to hang on anywhere temperatures dip below freezing regularly. How on Earth was a butterfly whose larva specialize on this family flitting around in temperate North America? What's more, reports place this species as far north as southern Quebec. I was obviously out of the loop on the taxonomic affinities of this family.

A little detective work turned up some surprising results. Temperate North America does in fact have some representatives of the citrus family. They are a far cry from an orange tree but they are nonetheless relatives. This inquiry actually solved a bit of trouble I was having with some riparian trees in my neck of the woods. As some of you probably know, trees are not a strong point of mine. I had encountered a few small woody things with compound leaves of three and dense clusters of greenish flowers. At first I thought I had found a rather robust poison ivy specimen but closer inspection revealed that wasn't the case.

Instead I had stumbled across something new for me - a common hoptree (Ptelea trifoliata). This cool looking tree is one of the giant swallowtails larval host trees, making it a member of -(you guessed it)- the citrus family. More often this small tree grows like a shrub with its tangle of multiple branches but they can reach some impressive heights, relatively speaking of course. Trees topping out at a height of 5 meters are not unheard of. Another common name of this tree - wafer ash - hints at its superficial similarity to a Fraxinus. Its compound leaves and wafer-like samaras are a bit of a curve ball for northerners like myself. It has a rather wide and patchy distribution throughout North America, and many subspecies/varieties have been named.

Common Hoptree (Ptelea trifoliata )

Common Hoptree (Ptelea trifoliata )

The other bit of this taxonomic journey involves another small tree, although this time I was better acquainted. Another host for the giant swallowtail is the prickly ash (Zanthoxylum americanum). It is interesting to note that both of these northern host trees superficially resemble ashes but I digress. The prickly ash is also small in stature and is most often found in thickets consisting of its own kind. As its common name suggests, you wouldn't want to go barreling through said thickets unless you wanted to donate some blood. It is well defended by sharp prickles on its stems. It does produce fruit but they are rather small and berry-like (technically follicles) and are distributed far and wide by birds.

Prickly Ash ( Zanthoxylum americanum )

Prickly Ash ( Zanthoxylum americanum )

Both trees are rather aromatic. They produce volatile oily compounds like most of the family, making them smell quite pleasant. Their small size makes them interesting specimen trees for anyone looking for something unique to put in a native landscape. What's more, they host a variety of other larvae as well, including those of the spicebush swallowtail butterfly (P. troilus).

Together, these two species are the most northerly representatives of the citrus family, making them quite special indeed. I am happy that my interest in attracting giant swallowtails to my property resulted in a fascinating dive into the geography of this interesting family.

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


Further Reading: [1] [2]

The Grasstree of Southwestern Australia

Southwestern Australia is home to one of the world's most unique floras. A combination of highly diverse, nutrient-poor soil types, bush fires, and lots of time have led to amazing adaptive radiations, the result of which are myriad plant species found nowhere else in the world. One of the most unique members of southwestern Australia's flora is the grassplant (Kingia australis). Like all plants of this region, it is one hardy species.

The taxonomic history of the grassplant has been a bit muddled. As its common name suggests, it was once thought to be a member of the genus Xanthorrhoea, however, its resemblance to this group is entirely superficial. It has since been placed in the family Dasypogonaceae. Along with three other genera, this entire family is endemic to Australia. Growing in southwestern Australia presents lots of challenges such as obtaining enough water and nutrients to survive and for the grassplant, these were overcome in some fascinating ways.

The way in which the grassplant manages this is quite incredible. Its trunk is not really a true trunk but rather a dense cluster of old leaf bases. Within this pseudotrunk, the grassplant grows a series of fine roots. Research has shown this to be an adaptation to life in a harsh climate. Because water can be scarce and nutrients are in short supply, the grassplant doesn't take any chances. Water hitting the trunk is rapidly absorbed by these roots as are any nutrients that come in the form of things like bird droppings.

Coupled with its underground roots, the grassplant is able to eek out a living. That being said, its life is spent in the slow lane. Plants are very slow growing and estimates place some of the larger individuals at over 600 years in age. Its amazing how some of the harshest environments can produce some of the longest lived organisms.

As you can probably imagine, reproduction in this species can also be a bit of a challenge. Every so often, flower clusters are produced atop long, curved stems. Their production is stimulated by fire but even then, with nutrients in poor supply, it is not a frequent event. Some plants have been growing for over 200 years without ever producing flowers. This lifestyle makes the grassplant sensitive to disturbance. Recruitment is limited, even in good flowering years and plants take a long time to mature. That is why conservation of their habitat is of utmost importance.

Photo Credits: [1] [2]

Further Reading: [1] [2]

The Mighty 'Ama'u

We tend to think of ferns as fragile plants, existing in the shaded, humid understories of forests. This could not be farther from the truth. Their lineage arose on this planet some 360 million years ago and has survived countless extinctions. In truth, they exhibit a staggering array of lifestyles, each with its own degree of adaptability. Take the Hawaiian tree fern, Sadleria cyatheoides for example.

Known in Hawai'i as the 'Ama'u, this tree fern is one of the first species to colonize the barren lava flows that make the Big Island so famous. This is an incredibly harsh landscape and many challenges must be overcome in order to persist. This does not seem to be an issue for the 'Ama'u. It is just as much at home in these water-starved habitats as it is in wetter forests. It is easily the most successful species in this genus, having colonized every island in the archipelago.

Much of its success has to due with a part of its life cycle that is much less obvious to us - the gametophyte stage. The tree fern we see is only half of the story. It is the spore-producing phase conveniently referred to as the sporophyte. When a spore finds a suitable site for germination, it grows into the other half of the life cycle, the gametophyte. This minute structure looks like a tiny green heart and it houses the reproductive organs of the plant. When water is present, male gametophytes release their flagellated sperm, which swim around until they find a female gametophyte to fertilize. Once fertilized, the resulting embryos will then grow into a new tree fern and start the cycle anew.

What sets the 'Ama'u apart from its rarer cousins is the fact that its gametophyte appears to be quite capable of both outcrossing and self-fertilization. Outcrossing, of course, promotes genetic diversity, however, the ability to self-fertilize means that a new plant can grow from only a single spore. This is super advantageous when it comes to colonizing new habitats. Its cousins seem to lack this ability to self-fertilize successfully, restricting them to more localized areas. Taken together, I think it's safe to say that the 'Ama'u is one tough cookie. 

Photo Credits: [1] [2]

Further Reading: [1] [2]

 

A Fern Unchanged

Ferns are old. Arising during the late Devonian period, some 360 million years ago, ferns once dominated the land. These ancient ferns were a bit different than the ferns we know today. It wasn't until roughly 145 million years ago, during the late Cretaceous period, that many extant fern families started to appear. However, a recent fossil discovery shows that at least one familiar fern was hanging out with dinosaurs as far back as 180 million years ago!

A team of scientists in Sweden recently unearthed an exquisitely preserve fossil of a fern from some early Jurassic deposits. Usually the fossilization process does not preserve very fine details, especially not at the cellular level, but that is not the case for this fossil. Falling into volcanic hydrothermal brine, the fern quickly mineralized. The speed at which the tissues of the fern were replaced by minerals preserved details that scientists usually only dream about. Clearly visible in the fossilized stem are subcellular structures like nuclei and even chromosomes in various stages of cell division!

 

source

source

Using sophisticated microscopy techniques, the team was able to analyze the properties of the nuclei undergoing division. What they discovered is simply amazing. The number of chromosomes as well as other properties of the DNA matched a fern that is quite common in eastern North America and Asia today. This fossilized fern, as far as the team can tell, is a cinnamon fern (Osmundastrum cinnamomeum). Based on the fossil evidence, cinnamon ferns were not only around during the early Jurassic, they have remained virtually unchanged for 180 million years. Talk about a living fossil!

Further Reading: [1]

1,730 New Plant Species Were Described in 2016

Manihot debilis

Manihot debilis

The discovery of a new animal species is celebrated the world over. At the same time, plants are lucky to ever make headlines. This is a shame considering that plants form the backbone of all terrestrial ecosystems. The conversation is starting to change, however, as more and more people are waking up to the fact that plants are fascinating organisms in their own right. In a recent addition of Kew Garden's State of the World's Plants, they report on 1,730 newly described plant species from all over the world.

Begonia rubrobracteolata

The discovery of these new plants species is truly a global event. Central and South America, Africa, tropical Asia, and Madagascar saw the addition of many intriguing taxonomic novelties. For instance, Malaysia can now add 29 new species of Begonia to their flora. Africa can now boast to be the home of the largest species of Bougainvillea in the world. Standing at 3 meters in height, it is an impressive sight to behold. Madagascar was particularly fruitful (pun intended), adding 150 new species, subspecies, and varieties of Croton all thanks to the diligent work of the late Alan Radcliffe-Smith. 

Commicarpus macrothamnum Photo Credit: Ib Friis

Commicarpus macrothamnum Photo Credit: Ib Friis

One of the most exciting finds from Madagascar was a new genus of climbing bamboos named Sokinochloa. So far only 7 species have been named. The key to unlocking the diversity of this new genus lies in their flowers, which are not produced on a regular basis. Like many bamboos, the Sokinochloa produce flowers at intervals of 10 to 50+ years. The new discoveries did not consist entirely of small understory herbs either. Some of those 1,730 plants were massive forest trees.

Sokinochloa australis

Sokinochloa australis

One of these new tree species is Africa's first endemic species of Calophyllum (Calophyllaceae). They were discovered during a survey for a uranium mine and, with fewer than 10 mature individuals, are considered critically endangered. Expeditions in Central America and the Andes turned up 27 new tree species in the genus Sloanea (Elaeocarpaceae) as well as 10 new species Trichilia, a genus of trees belonging to the mahogany family (Meliaceae).

The list could go on and on. Even more exiting is the fact that 2016 wasn't a particularly exceptional year for new plant discoveries. An estimated 2,000 new plant species are discovered on an annual basis. We aren't even close to grasping the full extent of plant diversity on this planet. What plants desperately need, however, is more attention. More attention leads to more scrutiny, more scrutiny leads to better understanding, and better understanding leads to improved conservation efforts. We could be doing a lot better with conservation efforts if we considered the plants whose very existence is essential for all life as we know it.

Barleria mirabilis Photo Credit: Quentin Luke

Barleria mirabilis Photo Credit: Quentin Luke

Tibouchina rosanae Photo Credit: W Milliken

Tibouchina rosanae Photo Credit: W Milliken

Englerophytum paludosum Photo Credit: Xander van der Burgt

Englerophytum paludosum Photo Credit: Xander van der Burgt

You can download your own copy of the State of the World's Plants by clicking here

All photos thanks to the Royal Botanical Gardens at Kew unless otherwise noted.

Can Plants "Hear" Running Water?

A recently published study suggests that some plants are capable of using sound to locate water. That's right, sound. Although claims of plants liking or disliking certain types of music still belong in the realm of pseudoscience, this research does suggest that plants may be capable of detecting vibrations in an interpretable way. 

To test this idea, Dr. Monica Gagliano of the University of Western Australia germinated pea seeds in specially designed mazes. Each maze looked like an upside-down Y. At the end of each arm, she devised a series of treatments that would force the pea seedlings to "choose" their desired rooting direction. In some treatments she used standing water coupled with water running through a tube. In others she simply played the sounds of running water against the sound of white noise.

The peas were allowed to grow for five days and afterwards were checked to see which direction their roots were growing. Amazingly, the peas seemed to be able to distinguish the sound of actual running water even when there was no moisture gradient present. Peas given the option of sitting or running water in a tube grew their roots towards the tube a majority of the time. Again, this was in the absence of any sort of water gradient in order to eliminate the chances that the peas were simply honing in on humidity.

Interestingly, plants that were played the sound of running water and white noise through speakers seemed to do what they could to avoid the noise. Although the research did not investigate why the peas had an aversion to the recordings, Dr. Gagliano suspects that it might have something to do with the low frequency magnetic currents emitted by the speakers. Previous research has shown that even weak localized magnetic fields are enough to disrupt the structure of developing root cells. 

All of this taken together paints a fascinating picture of plant sensory capabilities. One should take note, however, that the sample sizes used in this experiment were quite small. More, larger experiments will be needed to fully understand these patterns as well as the mechanisms behind them. Still, these findings shed light on cases in which tree roots seem to be so adept at finding sewer pipes, even in the absence of leaks. It also lends to the findings that the roots of trees such as scrub oaks and box elders will often opt for more stable and reliable sources of ground water over the fluctuating uncertainty of nearby stream sources. Finally, there is something to be said that we share as many as 10 of the 50 genes involved in human hearing with plants.

Our understanding of plant sensory capabilities is really starting to blossom (pun intended). Plants aren't the static, sessile organisms so many make them out to be. They are living, breathing organisms fighting for survival. I, for one, am excited for what new discoveries await. 

Photo Credits: [1] [2]

Further Reading: [1] [2]