How Trees Fight Disease

Plants do not have immune systems like animals. Instead, they have evolved an entirely different way of dealing with infections. In trees, this process is known as the "compartmentalization of decay in trees" or "CODIT." CODIT is a fascinating process and many of us will recognize its physical manifestations.

In order to understand CODIT, one must know a little something about how trees grow. Trees have an amazing ability to generate new cells. However, they do not have the ability to repair damage. Instead, trees respond to disease and injury  by walling it off from their living tissues. This involves three distinct processes. The first of these has to do with minimizing the spread of damage. Trees accomplish this by strengthening the walls between cells. Essentially this begins the process of isolating whatever may be harming the living tissues.

This is done via chemical means. In the living sapwood, it is the result of changes in chemical environment within each cell. In heartwood, enzymatic changes work on the structure of the already deceased cells. Though the process is still poorly understood, these chemical changes are surprisingly similar to the process of tanning leather. Compounds like tannic and gallic acids are created, which protect tissues from further decay. They also result in a discoloration of the surrounding wood. 

The second step in the CODIT process involves the construction of new walls around the damaged area. This is where the real compartmentalization process begins. The cambium layer changes the types of cells it produces around the area so that it blocks that compartment off from the surrounding vascular tissues. These new cells also exhibit highly altered metabolisms so that they begin to produce even more compounds that help resist and hopefully stave off the spread of whatever microbes may be causing the injury. Many of the defects we see in wood products are the result of these changes.

The third response the tree undergoes is to keep growing. New tissues grow around the infected compartment and, if the tree is healthy enough, will outpace further infection. You see, whether its bacteria, fungi, or a virus, microbes need living tissues to survive. By walling off the affected area and pumping it full of compounds that kill living tissues, the tree essentially cuts off the food supply to the disease-causing organism. Only if the tree is weakened will the infection outpace its ability to cope.

Of course, CODIT is not 100% effective. Many a tree falls victim to disease. If a tree is not killed outright, it can face years or even decades of repeated infection. This is why we see wounds on trees like perennial cankers. Even if the tree is able to successfully fight these repeat infections over a series of years, the buildup of scar tissues can effectively girdle the tree if they are severe enough.

CODIT is a well appreciated phenomenon. It has set the foundation for better tree management, especially as it relates to pruning. It is even helping us develop better controls against deadly invasive pathogens. Still, many of the underlying processes involved in this response are poorly understood. This is an area begging for deeper understanding.

Photo Credits: kaydubsthehikingscientist & Alex Shigo

Further Reading: [1]

The Strangest Wood Sorrel

Photo by Yastay licensed under CC BY-SA 4.0

For me, wood sorrels are a group of plants I usually have to look down to find. This is certainly not the case for Oxalis gigantea. Native to the coastal mountains of northern Chile, this bizarre Oxalis has forgone the traditional herbaceous habit of its cousins in exchange for a woody shrub-like growth form.

Photo by Jardín Botánico Nacional, Viña del Mar, Chile licensed under CC BY-NC 2.0

When I first laid eyes on O. gigantea, I thought I was looking at some strange form of Ocotillo. In front of me was a shrubby plant consisting of multiple upright branches that were covered in a dense layer of shiny green leaves occasionally interrupted by yellow flowers. You would think that at this point in my life, aberrant taxa would not longer surprise me. Think again. 

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

O. gigantea is one of the largest of the roughly 570 Oxalis species known to science. Its woody branches can grow to a height of 2 meters (6 feet)! The branches themselves are quite interesting to look at. They are covered in woody spurs from which clusters of traditional Oxalis-style leaves emerge. Each stem is capable of producing copious amounts of flowers all throughout the winter months. The flowers are said to be pollinated by hummingbirds but I was not able to find any data on this. 

Photo by Claudio Alvarado Solari licensed under CC BY-NC 2.0

This shrub is but one part of the Atacama Desert flora. This region of Chile is quite arid,  experiencing a 6 to 10 month dry season every year. What rain does come is often sparse. Any plant living there must be able to cope. And cope O. gigantea does! This oddball shrub is deciduous, dropping its leaves during the dryer months. During that time, these shrubs look pretty ragged. You would never guess just how lush it will become once the rains return. Also, it has a highly developed root system, no doubt for storing water and nutrients to tide them over.  

Photo by Jardín Botánico Nacional, Viña del Mar, Chile licensed under CC BY-NC 2.0

O. gigantea has enjoyed popularity as a horticultural oddity over the years. In fact, growing this shrub as a container plant is said to be quite easy. Despite its garden familiarity, O. gigantea is noticeably absent from the scientific literature. In writing this piece, I scoured the internet for any and all research I could find. Sadly, it simply isn't there.

This is all too often the case for unique and interesting plant species like O. gigantea. Like so many other species, it has suffered from the disdain academia has had for organismal research over the last few decades. We humans can and must do better than that. For now, what information does exist has come from horticulturists, gardeners, and avid botanizers from around the world. 

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

Further Reading: [1] [2] 

On the Ecology of Krameria

Photo by Stan Shebs licensed under CC BY-SA 3.0

There is something satisfying about saying "Krameria." Whereas so many scientific names act as tongue twisters, Krameria rolls of the tongue with a satisfying confidence. What's more, the 18 or so species within this genus are fascinating plants whose lifestyles are as exciting as their overall appearance. Today I would like to give you an overview of these unique parasitic plants.

Commonly known as rhatany, these plants belong to the family Krameriaceae. This is a monotypic clade, containing only the genus Krameria. Historically there has been a bit of confusion as to where these plants fit on the tree of life. Throughout the years, Krameria has been placed in families like Fabaceae and Polygalaceae, however, more recent genetic work suggests it to be unique enough to warrant a family status of its own. 

Regardless of its taxonomic affiliation, Krameria is a wonderfully specialized genus of plants with plenty of offer the biologically curious among us. All 18 species are shrubby, though at least a couple species can sometimes barely qualify as such. They are a Western Hemisphere taxon with species growing native as far south as Paraguay and Chile and as far north as Kansas and Colorado. They generally inhabit dry habitats.

Photo by Stan Shebs licensed under CC BY-SA 3.0

As I briefly mentioned above, most if not all of the 18 species are parasitic in nature. They are what we call "hemiparasites" in that despite stealing from their hosts, they are nonetheless fully capable of photosynthesis. It is interesting to note that no one (from what I have been able to find) has yet been able to raise these plants in captivity without a host. It would seem that despite being able to photosynthesize, these plants are rather specialized parasites. 

That is not to say that they have evolved to live off of a specific host. Far from it actually. A wide array of potential hosts, ranging from annuals to perennials, have been identified. What I find most remarkable about their parasitic lifestyle is the undeniable advantage it gives these shrubs in hot, dry environments. Research has found that despite getting a slow start on growing in spring, the various Krameria species are capable of performing photosynthesis during extremely stressful periods and for a much longer duration than the surrounding vegetation. 

Photo by mlhradio licensed under CC BY-NC 2.0

The reason for this has everything to do with their parasitic lifestyle. Instead of producing a long taproot to reach water reserves deep in the soil, these shrubs invest in a dense layer of lateral roots that spread out in the uppermost layers of soil seeking unsuspecting hosts. When these roots find a plant worth parasitizing, they grow around its roots and begin taking up water and nutrients from them. By doing this, Krameria are not limited by what water or other resources their roots can find in the soil. Instead, they have managed to tap into large reserves that would otherwise be locked away inside the tissues of their neighbors. As such, the Krameria do not have to worry about water stress in the same way that non-parasitic plants do. 

Photo by Stan Shebs licensed under CC BY-SA 3.0

By far the most stunning feature of the genus Krameria are the flowers. Looking at them it is no wonder why they have been associated with legumes and milkworts. They are beautiful and complex structures with a rather specific pollination syndrome. Krameria flowers produce no nectar to speak of. Instead, they have evolved alongside a group of oil-collecting bees in the genus Centris.

One distinguishing feature of Krameria flowers are a pair of waxy glands situated on each side of the ovary. These glands produce oils that female Centris bees require for reproduction. Though Centris bees are not specialized on Krameria flowers, they nonetheless visit them in high numbers. Females alight on the lip and begin scraping off oils from the glands. As they do this, they inevitably come into contact with the stamens and pistil. The female bees don't feed on these oils. Instead, they combine it with pollen and nectar from other plant species into nutrient-rich food packets that they feed to their developing larvae.  

Photo by João Medeiros licensed under CC BY 2.0

Following fertilization, seeds mature inside of spiny capsules. These capsules vary quite a bit in form and are quite useful in species identification. Each spine is usually tipped in backward-facing barbs, making them excellent hitchhikers on the fur and feathers of any animal that comes into contact with them.  

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

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

The Bladderwort Microbiome Revealed

Photo by Stefan.lefnaer licensed under CC BY-SA 3.0

The bladderworts (Utricularia spp.) are among the most cosmopolitan groups of carnivorous plants on this planet. Despite their popularity, their carnivorous habits have been subject to some debate. Close observation reveals that prey capture rates are surprisingly low for most species. This has led some to suggest that the bladderworts may be benefiting from more passive forms of nutrient acquisition. To better understand how these plants utilize their traps, a team of researchers decided to take a closer look at the microbiome living within. 

The team analyzed the trap fluid of a handful of floating aquatic bladderwort species - U. vulgaris, U. australis, and U reflexa. In doing so, they uncovered a bewildering variety of microorganisms perfectly at home within the bladderwort traps. Thanks to sophisticated genetic tools, they were able to classify these microbes in order to investigate what exactly they might be doing inside the traps. 

Their findings were quite astonishing to say the least. The traps of these plants harbor extremely rich microbial communities, far richer than the microbial diversity of other carnivorous plant traps. In fact, the richness of these microbial communities were more akin to the richness seen in the rooting zone of terrestrial plants or the gut of a cow. In terms of the species present, the microbial communities of bladderwort traps most closely resembled that of the pitchers of Sarracenia species as well as the guts of herbivorous iguanas.

Photo by Michal Rubeš - http://www.darwiniana.cz/vamr/?page=obrazek&id=914 licensed under CC BY 4.0

The similarities with herbivore guts is quite remarkable. Its not just coincidental either. The types of microbes they found weren't new to science but their function was a bit of a surprise. A large percentage of the bacteria living within the fluid are famously known for producing enzymes that digest complex plant tissues. Similarly, the team found related microbe groups that specialize on anaerobic fermentation. These types of microbes in particular are largely responsible for the breakdown of plant materials in the rumen of cattle.

As it turns out, the microbes living within the traps of these bladderworts are serving a very important purpose for the plant - they are breaking down plant and algae cells that find their way into the traps each time they open and close. In doing so, they give off valuable nutrients that the bladderworts can then absorb and utilize. Let me say that again, the bacteria living in bladderwort traps are digesting algae and other plant materials that these carnivorous plants can then absorb.

Now these bacteria are also responsible for producing a lot of methane in the process. Interestingly enough, the team was not able to detect measurable levels of methane leaving the traps. This would be odd if it wasn't for the community of methane-feeding microbes also discovered living within the traps. The team believes that these organisms metabolize all of the methane being produced before it can escape the traps. 

As remarkable as these findings are, I don't want to give the impression that these carnivorous plants have taken up a strict vegetarian lifestyle. The team also found myriad other microorganisms within the bladder traps, many of them being carnivores themselves. The team also found a rich protist community. A majority of these were euglenids and ciliates. 

These sorts of protists are important microbial predators and the numbers recorded within the traps suggest that they are a rather significant component of these trap communities. As they chase down and consume bacteria and other protists, they release valuable nutrients that the plants can absorb and utilize. Numbers of these predatory protists were much higher in older traps, which have had much more time to accumulate a diverse microbiome. Astonishingly, it is estimated that the protist communities can cycle the entire contents of the bladderwort traps upwards of 4 or 5 times in a 24 hour period. That is some serious turnover of nutrients!

The protists weren't the only predators found within the traps either. There are also a considerable amount of bacterial predators living there as well. These not only cycle nutrients in similar ways to the protist community, it is likely they also exhibit strong controls on the biodiversity within this miniature ecosystem. In other words, they are considered keystone predators of these microcosms.

Also present within the traps were large amounts of fungal DNA. None of the species they found are thought to actually live within the traps. Rather, it is thought that they are taken up as spores blown in from the surrounding environment. Exactly how these organisms find themselves living inside bladderwort traps is something worth considering. The plants themselves are known for being covered in biomfilms. It is likely that many of the organisms living within the traps were those found living on the plants originally. 

Taken together, the remarkable discovery of such complex microbial communities living on and within these carnivorous plants shows just how complex the ecology of such systems really are. Far from the active predators we like to think of them as, the bladderworts nonetheless rely on a mixture of symbiotic orgnaisms to provide them with the nutrients that they need. The fact that these plants are in large part digesting plant and algae materials is what I find most astonishing.

Essentially, one can almost think of bladderworts as plants adorned with tiny, complex cow stomachs, each utilizing their microbial community to gain as much nutrients as they can from their living environment. The bladderworts gain access to nutrients and the microbes get a place to live. The bladderworts really do seem to be cultivating a favorable habitat for these organisms as well. Analysis of the bladder fluid demonstrated that the plants actively regulate the pH of the fluid to maintain their living community of digestive assistants. In doing so, they are able to offset the relative rarity of prey capture. Keep in mind that this research was performed on only three species of bladderwort originating from similar habitats. Imagine what we will find in the traps of the multitude of other Utricularia species.

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

Further Reading: [1]

This Isn't Even My Final Form! A Pothos Story

Photo by Forest and Kim Starr licensed under CC BY 2.0

Pothos might be one of the most widely cultivated plants in modern history. These vining aroids are so common that I don't think I can name a single person in my life that hasn't had one in their house at some point or another. Renowned for their hardy disposition and ability to handle extremely low light conditions, they have become famous the world over. They are so common that it is all too easy to forget that they have a wild origin. What's more, few of us ever get to see a mature specimen. The plants living in our homes and offices are mere juveniles, struggling to hang on as they search for a canopy that isn't there.

Trying to find information on the progenitors of these ubiquitous houseplants can be a bit confusing. To do so, one must figure out which species they are talking about. Without a proper scientific name, it is nearly impossible to know which plant to refer to. Common names aside, pothos have also undergone a lot of taxonomic revisions since their introduction to the scientific community. Also, what was thought to be a single species is actually a couple.

Photo by Forest and Kim Starr licensed under CC BY 2.0

To start with, the plants you have growing in your home are no longer considered Pothos. The genus Pothos seemed to be a dumping ground for a lot of nondescript aroid vines throughout the last century. Many species were placed there until proper materials were thoroughly scrutinized. Today, what we know as a "Pothos" has been moved into the genus Epipremnum. This revision did not put all controversies to rest, however, as the morphological changes these plants go through as they age can make things quite tricky.

Photo by Tauʻolunga licensed under CC BY-SA 3.0

As I mentioned, the plants we keep in our homes are still in their juvenile form. Like all plants, these vines start out small. When they find a solid structure in a decent location, they make their bid for the canopy. Up in a tree in reach of life giving sunlight, these vines really hit their stride. They quickly grow their own version of a canopy that consists of massive leaves nearing 2 feet in length! This is when these plants begin to flower. 

As is typical for the family, the inflorescence consists of a spadix covered by a leafy spathe. The spadix itself is covered in minute flowers and these are the key to properly identifying species. When pothos first made its way into the hands of botanists, all they had to go on were the small, juvenile leaves. This is why their taxonomy had been such a mess for so long. Materials obtained in 1880 were originally named Pothos aureus. It was then moved into the genus Scindapsus in 1908.

Controversy surrounding a proper generic placement continued throughout the 1900's. Then, in the early 1960's, an aroid expert was finally able to get their hands on an inflorescence. By 1964, it was established that these plants did indeed belong in the genus Epipremnum. Sadly, confusion did not end there. The plasticity in forms and colors these vines exhibit left many confusing a handful of species within the group. At various times since the late 1960's, E. aureum and E. pinnatum have been considered two forms of the same species as well as two distinct species. The latest evidence I am aware of is that these two vines are in fact distinct enough to warrant species status. 

Photo by Mokkie licensed under CC BY-SA 3.0

The plant we most often encounter is E. aureum. Its long history of following humans wherever they go has led to it becoming an aggressive invader throughout many regions of the world. It is considered a noxious weed in places like Australia, Southeast Asia, India, Pakistan, and Hawai'i (just to name a few). It does so well in these places that it has been a little difficult to figure out where these plants originated. Thanks to some solid detective work, E. aureum is now believed to be native to Mo'orea Island off the west coast of French Polynesia. 

Epipremnum pinnatum is similar until you see an adult plant. Photo by Mokkie licensed under CC BY-SA 3.0

It is unlikely that most folks have what it takes to grow this species to its full potential in their home. They are simply too large and require ample sunlight, nutrients, and humidity to hit their stride. Nonetheless there is something to be said for the familiarity we have with these plants. They have managed to enthrall us just enough to be a fixture in so many homes, offices, and shopping centers. It has also helped them conquer far more than the tiny Pacific island on which they evolved. Becoming an invasive species always seems to have a strong human element and this aroid is the perfect example.

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

Further Reading: [1] [2] [3] 

Gnetum Are Neat!

Photo by gbohne licensed under CC BY-SA 2.0

As much as I hate to admit it, when I think of gymnosperms my mind autopilots to conifers and ginkgos. I too easily forget about some of the other extant gymnosperm lineages with which we share space on this planet. Whereas one can easily pick out a conifer or a ginkgo from a lineup, some of the other gymnosperms aren't readily recognized as such. One group in particular challenges my gymnosperm search image to the extreme. I am, of course, talking about a family of gymnosperms known as Gnetaceae.

Gnetaceae is home to a single genus, Gnetum, of which there are about 40 species. They can be found growing in tropical forests throughout South America, Africa, and Southeast Asia. Gnetum essentially come in two forms, small trees and larger, scrambling vines. To most passersby, the various Gnetum species appear to be yet another tropical angiosperm with elliptical evergreen leaves. Indeed, the various species of Gnetum exhibit features that suggest a close link with flowering plants. This has led some to hypothesize that they represent a sort of living "link" between gymnosperms and angiosperms. We will get to that in a bit. First, we must taker a closer look at these odd plants.

Photo by Forest and Kim Starr licensed under CC BY 2.0

We will start with their leaves. They are quite strange by gymnosperm standards. Gnetum produce elliptical leaves with reticulate or web-like venation. Also, their vascular tissues contain vessel elements. Such traits are usually associated with dicotyledonous angiosperms. Characteristics such as these explain why the taxonomic position of Gnetaceae has floundered a bit over the years. What about reproduction? Surely that can help gain a better understanding of where this groups stands taxonomically.

Gnetum reproductive bits require a bit of scrutiny. They are certainly not what we would call flowers. They aren't quite cones either. The technical term for gymnosperm reproductive structures are stobili. In Gnetum, these arise from the axils of the leaves. They are strange looking structures to say the least. Male strobili are long and cylindrical. They, of course, produce pollen. They also contain infertile ovules whose function I will get to in a minute. Female strobili, on the other hand, are larger and consist of ovules enclosed in a thin tissue or integument.

Photo by Kware Ji licensed under CC BY 2.0

Pollination in Gnetum is largely accomplished via insects, though wind plays a significant role for some species as well. In insect pollinated species, the female strobili emit a strong odor and secret tiny beads of liquid called "pollination droplets." Pollination droplets are also secreted from the sterile ovules on the male strobili. It was observed that moths were the main visitors for at least two species of Gnetum.  The reason both sexes produce pollination droplets is to ensure that moths will visit multiple individuals in their search for food.

Following pollen transfer, even more angiosperm-like activity takes place. Some Gentum undergo a type of double fertilization that is unique among moat gymnosperm lineages. Double fertilization is largely considered a defining feature of flowering plants. It is a process by which two sperm cells unite with an egg and become the embryo and the nutritive endosperm that will fuel seedling growth. Along with its cousin Ephedra, Gnetum double fertilization also involves two sperm cells, though the end result is a bit different. Instead of forming an embryo and an endosperm, double fertilization in Gentum (and Ephedra) results in the formation of two viable zygotes and no endosperm.

Photo by Forest and Kim Starr licensed under CC BY 2.0

Fertilized seeds gradually swell into large drupe-like structures. Integument tissues develop with the seed, covering it in a fruit-like substance that turns from green to red as it matures. As far as anyone knows, birds are the main seed dispersal agents for most Gnetum species. 

Taken together, their peculiar anatomy and intriguing pollination have led many to suggest that Gnetum are more closely allied to flowering plants than they are gymnosperms. Certainly it is easy to draw lines from one dot to another in this case but the real test lies in DNA. Are they highly derived gymnosperms or possibly a so-called missing link? 

No. Recent work by the Angiosperm Phylogeny Group found that Gnetaceae are more closely related to the family Pinaceae than they are any of the sister angiosperm lineages. Their work also revealed that, although this lineage arose some 250 million years ago, much of the diversity we see today is the result of rapid speciation events during the Oligocene and Miocene. It would appear that these derived gymnosperms are not the missing link they we once thought to be. In fact, the whole concept of an evolutionary missing link is flawed to begin with. 

Photo by Ahmad Fuad Morad licensed under CC BY-NC-SA 2.0

Still, this should not take away from fully appreciating the bizarre nature of this family. The uniqueness of the genus Gnetum is certainly worth celebrating. They serve as a reminder of just how diverse gymnosperms once were. Today they are a mere shadow of their former glory, overshadowed by the bewildering diversity of angiosperms. If you encounter a Gnetum, take the time to appreciate it as a representative of just how strange gymnosperms can be. 

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

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

Getting to Know Elodea

Photo by Christian Fischer licensed under CC BY-SA 3.0

When I think back on it, one of the first plants I ever actively tried growing was waterweed (Elodea canadensis). My 4th grade teacher had invested in a unit on the ecosystem concept. We all brought in 2 liter soda bottles that we craftily turned into mini terrariums. The top half of the terrarium was filled with soil and planted with some grass seed. The bottom half was filled with water and some gravel. In that portion we placed a single guppy and a few sprigs of Elodea. 

The idea was to teach us about water and nutrient cycles. It didn't work out too well as most of my classmates abandoned theirs not long after the unit was over. Being the avid little nerd that I was, I fell deeply in love with my new miniature ecosystem. The grass didn't last long but the guppy and the Elodea did. Since then, I have kept Elodea in various aquariums throughout the years but never gave it much thought. It is easy enough to grow but it never did much. Today I would like to make up for my lack of concern for this plant by taking a closer look at Elodea. 

An example of the soda bottle terrariums. Photo by Kara Nelson [source]

The genus Elodea is one of 16 genera that make up the family Hydrocharitaceae and is comprised of 6 species. All 6 of these plants are native to either North or South America, with Elodea canadensis preferring the cooler regions of northern North America. They are adaptable plants and can grow both rooted or floating in a variety of aquatic conditions. It is this adaptability that has made them so popular in the aquarium trade. It is also the reason why the genus is considered a nasty aquatic invasive throughout the globe. For this reason, I do not recommend growing this plant outdoors in any way, shape, or form unless that species is native to your region. 

Believe it or not, Elodea are indeed flowering plants. Small white to pink flowers are borne on delicate stalks at the water's surface. They are attractive structures that aren't frequently observed. In fact, it is such a rare occurrence that trying to figure out what exactly pollinates them proved to be quite difficult. What we do know is that sexual reproduction and seed set is not the main way in which these plants reproduce. 

Photo by R a mueller licensed under CC BY-SA 3.0

Anyone who has grown them in an aquarium knows that it doesn't take much to propagate an Elodea plant. They have a remarkable ability for cloning themselves from mere fragments of the stem. This is yet another reason why they can become so invasive. Plants growing in temperate waterways produce a thick bud at the tips of their stems come fall. This is how they overwinter. Once favorable temperatures return, this bud "germinates" and grows into a new plant. In more mild climates, these plants are evergreen. 

One of the most interesting aspects of Elodea ecology is that at least two species, E canadensis and E. nuttallii, are considered allelopathic. In other words, these plants produce secondary chemicals in their tissues that inhibit the growth of other photosynthetic organisms. In this case, their allelopathic nature is believed to be a response to epiphytic algae and cyanobacteria.

Slow growing aquatic plants must contend with films of algae and cyanobacteria building up on their leaves. Under certain conditions, this buildup can outpace the plants' ability to deal with it and ends up completely blocking all sunlight reaching the leaves. Researchers found that chemicals produced by these two species of Elodea actually inhibited the growth of algae and cyanobacteria on their leaves, thus reducing the competition for light in their aquatic environments. 

Elodea make for a wonderful introduction to the world of aquatic plants. They are easy to grow and, if cared for properly, look really cool. Just remember that their hardy nature also makes them an aggressive invader where they are not native. Never ever dump the contents of an aquarium into local water ways. Provided you keep that in mind, Elodea can be a wonderful introduction to the home aquarium. If you are lucky enough to see them in flower in the wild, take the time to enjoy it. Who knows when you will see it again. 

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

Further Reading: [1] [2] 

A Surprising Realization About Leaf Windows

I will never forget the first time I laid eyes on a Lithops. These odd little succulents are truly marvels of evolution. The so-called "living stones" really do earn their name as most are exquisitely camouflaged to match the gravelly soils in which they grow. If bizarre color patterns weren't enough, Lithops, as well as many other succulents, live their lives almost completely buried under the soil. All one ever really sees is the very tip of their succulent leaves and the occasional flower.

It is the tips of those leaves that make people swoon. Lithops belong to a hodgepodge mix of succulent genera and families that produce windowed leaves. Aside from their striking patterns, the tips of their leaves are made up of layers of translucent cells, which allow light to penetrate into the interior of the leaf where the actual photosynthetic machinery is housed. Their semi-translucent leaves, coupled with their nearly subterranean habit, have led to the assumption that the leaf windows allow the plants to continue photosynthesis all the while being mostly buried. Despite the popularity of this assumption, few tests had been performed to see whether or not the windows function as we think. All of that changed back in the year 2000.

As hinted at above, a variety of succulent plants have converged on a similar leaf morphology. This is where things get a bit strange. Not all plants that exhibit the leaf window trait find themselves buried in the soil. Others, such as Peperomia graveolens for example, produce the photosynthetic tissues on tall stems. Examples like this led at least some researchers to second guess the common assumption of windows increasing photosynthesis and the resulting investigations were surprising to say the least. 

Peperomia graveolens. © Raimond Spekking / CC BY-SA 4.0 (via Wikimedia Commons)

A duo of researchers decided to test the assumption that leaf windows increase photosynthesis by channeling light directly to the photosynthetic machinery inside. The researchers used tape to cover the leaf windows of a variety of succulent plant species. When they compared photosynthetic rates between the two groups, not a single difference was detected. Plants who had their leaves covered photosynthesized the same amount as plants with uncovered leaves. These data were quite shocking. Because they tested this assumption across a variety of plant species, the results suggested that the function of windowed leaves isn't as straight forward as we thought. These findings raised more questions than they solved.

Subsequent experiments only served to reinforce the original findings. What's more, some even showed that plants with covered windows actually photosynthesized more than plants with uncovered windows. It seems that windowed leaves function in a completely opposite manner than the popular assumption. The key to this patterns may lie in heat exchange. When the researchers took the temperature of the interior of the leaves in each group, they found that internal leaf temperatures were significantly higher in the uncovered group and this has important implications for photosynthesis for these species.

High leaf temperatures can be extremely damaging to photosynthetic proteins. If too much light filters through, leaf temperatures can actually hit damaging levels. This is one reason that many of these plant species have adopted this bizarre semi-subterranean habit. Plants that experienced such high temperatures throughout the course of a day had permanent damage done to their photosystems. This led to a reduction of fitness over time. Such lethal temperature spikes did not happen to leaves that had been covered.

Haworthia truncata. Photo by www.haworthia-gasteria.com

If you're anything like me, at this point you must be questioning the role of the leaf windows entirely. Why would they be there if they may actually hurt the plants in the long run? Well, this is where knowing something about the habitat of each species comes into play. Not all leaf windows are created equal. The patterns of their windows vary quite a bit depending on where the plants evolved. In 2012, a paper was published that looked at the patterns of Lithops leaf windows in relation to their place of origin. Not all Lithops grow in the same conditions and various species hail from regions with vastly different climates.

What the paper was able to demonstrate was that Lithops native to regions that experience more average annual rainfall have much larger window areas on their leaves than Lithops native to drier regions. Again, the underpinnings of this discovery nonetheless have to do with light availability. Wetter areas experience more cloud cover than drier areas so Lithops growing where its cloudy have to cope with a lot less sun than their more xeric-growing cousins. As such, having a larger window allows more diffuse light into the leaf for photosynthesis without having to worry about the damaging temperatures.

Photo by Petra licensed under CC BY-NC 2.0

The reverse is true for Lithops from drier climates. They have smaller leaf windows because they experience more days with direct sun. Smaller windows means less sunlight entering the leaf. This serves to keep internal leaf temperatures within a much safer range, thus protecting the delicate proteins inside. As it turns out, leaf windows seem to represent a trade-off between photosynthesis and overheating. What's more, some window-leaved species seem to be evolving away from the light transmitting function of their cousins living in shadier conditions. If anything, this serves as a reminder that simply because something seems obvious, that doesn't mean its always true. Stay curious, my friends!

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

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

The Extraordinary Catasetum Orchids

Male Catasetum osculatum. Photo by Orchi licensed under CC BY-SA 3.0

Orchids, in general, have perfect flowers in that they contain both male and female organs. However, in a family this large, exceptions to the rules are always around the corner. Take, for instance, orchids in the genus Catasetum. With something like 166 described species, this genus is interesting in that individual plants produce either male or female flowers. What's more, the floral morphology of the individual sexes are so distinctly different from one another that some were originally described as distinct species. 

Female Catasetum osculatum. Photo by Valdison Aparecido Gil licensed under CC BY-SA 4.0

In fact, it was Charles Darwin himself that first worked out that plants of the different sexes were indeed the same species. The genus Catasetum enthralled Darwin and he was able to procure many specimens from his friends for study. Resolving the distinct floral morphology wasn't his only contribution to our understanding of these orchids, he also described their unique pollination mechanism. The details of this process are so bizarre that Darwin was actually ridiculed by some scientists of the time. Yet again, Darwin was right. 

Catasetum longifolium. Photo by Maarten Sepp licensed under CC BY-SA 4.0

If having individual male and female plants wasn't strange enough for these orchids, the mechanism by which pollination is achieved is quite explosive... literally. 

Catasetum orchids are pollinated by large Euglossine bees. Attracted to the male flowers by their alluring scent, the bees land on the lip and begin to probe the flower. Above the lip sits two hair-like structures. When a bee contacts these hairs, a structure containing sacs of pollen called a pollinia is launched downwards towards the bee. A sticky pad at the base ensures that once it hits the bee, it sticks tight. 

Male Catasetum flower in action. Taken from BBC's Kingdom of Plants.

Bees soon learn that the male flowers are rather unpleasant places to visit so they set off in search of a meal that doesn't pummel them. This is quite possibly why the flowers of the individual sexes look so different from one another. As the bees visit the female flowers, the pollen sacs on their back slip into a perfect groove and thus pollination is achieved. 

The uniqueness of this reproductive strategy has earned the Catasetum orchids a place in the spotlight among botanists and horticulturists alike. It begs the question, how is sex determined in these orchids? Is it genetic or are there certain environmental factors that push the plant in either direction? As it turns out, light availability may be one of the most important cues for sex determination in Catasetum. 

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

A paper published back in 1991 found that there were interesting patterns of sex ratios for at least one species of Catasetum. Female plants were found more often in younger forests whereas the ratios approached an even 1:1 in older forests. What the researchers found was that plants are more likely to produce female flowers under open canopies and male flowers under closed canopies. In this instance, younger forests are more open than older, more mature forests, which may explain the patterns they found in the wild. It is possible that, because seed production is such a costly endeavor for plants, individuals with access to more light are better suited for female status. 

Catasetum macrocarpum. Photo by maarten sepp licensed under CC BY-SA 2.0

Aside from their odd reproductive habits, the ecology of these plants is also quite fascinating. Found throughout the New World tropics, Catasetum orchids live as epiphytes on the limbs and trunks of trees. Living in the canopy like this can be stressful and these orchids have evolved accordingly. For starters, they are deciduous. Most of the habitats in which they occur experience a dry season. As the rains fade, the plants will drop their leaves, leaving behind a dense cluster of green pseudobulbs. These bulbous structures serve as energy and water stores that will fuel growth as soon as the rains return. 

Catasetum silvestre in situ. Photo by Antonio Garces licensed under CC BY-NC-ND 2.0

The canopy can also be low in vital nutrients like nitrogen and phosphorus. As is true for all orchids, Catasetum rely on an intimate partnership with special mychorrizal fungi to supplement these ingredients. Such partnerships are vital for germination and growth. However, the fungi that they partner with feed on dead wood, which is low in nitrogen. This has led to yet another intricate and highly specialized relationship for at least some members of this orchid genus. 

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

Mature Catasetum are often found growing right out of arboreal ant nests. Those that aren't will often house entire ant colonies inside their hollowed out pseudobulbs. This will sometimes even happen in a greenhouse setting, much to the chagrin of many orchid growers. The partnership with ants is twofold. In setting up shop within the orchid or around its roots, the ants provide the plant with a vital source of nitrogen in the form of feces and other waste products. At the same time, the ants will viciously attack anything that may threaten their nest. In doing so, they keep many potential herbivores at bay.  

Female Catasetum planiceps. Photo by sunoochi licensed under CC BY 2.0

To look upon a flowering Catasetum is quite remarkable. They truly are marvels of evolution and living proof that there seems to be no end to what orchids have done in the name of survival. Luckily for most of us, one doesn't have to travel to the jungles and scale a tree just to see one of these orchids up close. Their success in the horticultural trade means that most botanical gardens house at least a species or two. If and when you do encounter a Catasetum, do yourself a favor and take time to admire it in all of its glory. You will be happy that you did. 

Photo Credits: [1] [2] [3] [4] [5] [6] [7] [8] [9] 

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

Poinsettias Wild Origins

Photo by Dinesh Valke licensed under CC BY-SA 2.0

Poinsettias are famous the world over for the splash of color they provide indoor spaces during the colder months of the year. The name "poinsettia" is seemingly synonymous with the holiday season. They are so common that it is all too easy to write them off as another disposable houseplant whose only purpose is to dazzle us with a few short weeks of reds and whites. With all of the focus on those colorful bracts, it is also easy to lose sight of the fact that these plants have wild origins. What exactly is a poinsettia and where do they come from?

Poinsettia is the common name given to a species of shrub known scientifically as Euphorbia pulcherrima. No one quite knows the exact origin of our cultivated house guests but the species itself is native to the mountains of the Pacific slope of Mexico. It is a scraggly shrub that lives in seasonally dry tropical forests. Mature specimens can grow to be so large and lanky that they almost resemble vines. As many of you know, the poinsettias we use to decorate our homes never reach the same sizes as their wild counterparts. The reason for this is because all cultivated poinsettias have been purposely infected with a bacteria that stunts their growth, keeping them small and compact.

Photo by Frank Vincentz licensed under CC BY-SA 3.0

These shrubs flower throughout winter and into spring. What we think of as large, showy, red and white flower petals are not petals at all. They are actually leafy bracts. Like a vast majority of Euphorbia species, E. pulcherrima produces a special type of inflorescence called a cyathium. The flowers themselves are small, yellow, and not much to look at with the naked eye. However, take a hand lens to them and you will reveal rather intriguing little structures. What the flowers lack in showy display is made up for by the colorful bracts, which serve similar functions as petals in that their stunning colors are there to attract potential pollinators. 

Those bracts also caught the attention of horticulturists. Because of their beauty, E. pulcherrima is one of the most widely cultivated plants in human history. As many a poinsettia owner has come to realize, the bracts do not stay colored up all year. In fact, the whole function of these bracts is to save energy on flower production by coloring up leaves that are already in place. If they don’t have to produce pigments, they won’t and for much of the year, the bracts are largely green. The key to the color change lies in Earth’s axial tilt.

Photo by Gavin White licensed under CC BY-NC-ND 2.0

As the northern hemisphere begins to tilt away from the sun, days grow shorter. In turn, poinsettia plants begin to mature their flowers. At the same time, changes within the leafy bracts cause them to start producing pigments. When the days become shorter than the nights, the plants go into full reproductive mode. Both red- and white-colored bracts have been found in the wild. As soon as the days start to grow longer than the nights, the plants switch out of reproductive mode and the dazzling color fades. In captivity, this change is mimicked by plunging plants into complete darkness for a minimum of 12 hours per day.

Photo by Kahunapule Michael Johnson licensed under CC BY-NC-SA 2.0

Another aspect worth considering about this species is its sap. Whereas most plants hailing from Euphorbiacea or spurge family contain toxic sap, the sap of E. pulcherrima is very mild in its toxicity and an absurd amount of plant material would have to be consumed to suffer any serious side effects. Certainly it serves an anti-herbivore purpose in the wild, however, as long as you're not a tiny insect or a gluttonous deer, you have nothing to worry about from this species at least. So there you have it, some food for thought if you feel the urge to purge some spurge in a post-holiday cleanse. Condsider keeping these wonderful plants in your home for another year. If you follow their natural daylight cycle, you may just coax some color out of them for many winters to come.

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

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

This Is Not The Bamboo You Are Looking For...

Photo by Benoit Giroux licensed under CC BY-NC-SA 2.0

She has one, he has one, you have one, I have one, the office has one... lets just say "lucky bamboo" has made its way into many a home, office, and waiting room. Popularized by the practice of feng shui and sold for pennies on the dime by New Age stores all over the world, these plants seem to thrive on neglect. It may come as a surprise then that these plants are not a bamboo at all.

These ubiquitous home decorations are actually a species of Dracaena, Dracaena braunii to be exact. It isn't even from the same taxonomical order as bamboo. Whereas bamboo are a type of grass, D. braunii is actually more closely related to lilies. Hailing from Africa, D. braunii grows as an understory shrub in rainforests. This may explain why it does so well in the nutrient poor, low light conditions of most homes. 

In the wild, it can grow upwards of 5 feet tall. In captivity, however, it rarely exceeds 3 feet.. While most people grow theirs in a container of water and pebbles, D. braunii can do equally as well, if not better in potting mix.

Photo Credit: Benoit Giroux

Further Reading: [1]

The Traveler's Palm

© CEphoto, Uwe Aranas licensed under CC BY-SA 3.0

This nifty looking tree is commonly referred to as the traveler's palm (Ravenala madagascariensis). In reality, it is not a palm at all but rather a close cousin of the bird of paradise plants (Strelitziaceae). It is endemic to Madagascar and the only member of its genus. Even more fascinating is its relationship with another uniquely Madagascan group - the lemurs. But first we must ask, what's in a name?

The name "traveler's palm" has two likely explanations. The first has to do with the orientation of that giant fan of leaves. The tree is said to align its photosynthetic fan in an east-west orientation, which can serve as a crude compass, allowing weary travelers to orient themselves. I found no data to support this. The other possibility comes from the fact that this tree collects a lot of water in its nooks and crannies. Each of its hollow leaf bases can hold upwards of a quart of rain water! Get to it quick, though, because these water stores soon stagnate.

Photo by H. Zell licensed under CC BY-SA 3.0

Flowers are produced between the axils of the leaves and closely resemble those of its bird of paradise cousins. Closer observation will reveal that they are nonetheless unique. For starters, they are large and contained within stout green bracts. Also, they are considerably less showy than the rest of the family. They don't produce any strong odors but they do fill up with copious amounts of sucrose-rich nectar. Finally, the flowers remain closed, even when mature and are amazingly sturdy structures. It may seem odd for a plant to guard its flowers so tightly until you consider how they are pollinated.

It seems fitting that an endemic plant like the traveler's palm would enter into a pollination syndrome with another group of Madagascar endemics. As it turns out, lemurs seem to be the preferred pollinators of this species. Though black lemurs, white fronted lemurs, and greater dwarf lemurs have been recorded visiting these blooms, it appears that the black-and-white ruffed lemur manages a bulk of the pollination services for this plant.

Watching the lemurs feed, one quickly understands why the flowers are so stout. Lemurs force open the blooms to get at the nectar inside. The long muzzles of the black-and-white ruffed lemur seem especially suited for accessing the energy-rich nectar within. The flowers themselves seem primed for such activity as well. The enclosed anthers are held under great tension. When a lemur pries apart the petals, the anthers spring forward and dust its muzzle with pollen. Using both its hands and feet, the lemur must wedge its face down into the nectar chamber in order to take a sip. In doing so, it inevitably comes into contact with the stigma. Thus, pollination is achieved. Once fertilized, the traveler's palm produces seeds that are covered in beautiful blue arils.

Photo by Jeffdelonge licensed under CC BY-SA 3.0

All in all, this is one unique plant. Though its not the only plant to utilize lemurs as pollinators, it is nonetheless one of the more remarkable examples. Its stunning appearance has made it into something of a horticultural celebrity and one can usually find the traveler's palm growing in larger botanical gardens around the world. Though the traveler's palm itself is not endangered, its lemur pollinators certainly are. As I have said time and again, plants do not operate in a vacuum. To save a species, one must consider the entirety of its habitat. This is why land conservation is so vitally important. Support a land conservancy today!

Photo Credits: [1] [2]

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

Why Do Rhododendron Leaves Droop and Curl in the Winter?

Photo by Hanna Sörensson licensed under CC BY-SA 2.0

Broad leaved, evergreen plants living in the temperate regions of the world face quite a challenge come winter time. Freezing temperatures, lack of water, and often intense sun can exact quite a toll on living tissues. These are likely just some of the reasons why, relatively speaking, broad leaved evergreens are a rare occurrence in temperate zones. By far the most popular group of plants in this category are the Rhododendrons.

Many a Rhodo lover has said that they can tell how cold it is outside by looking at Rhododendron leaves. Indeed, as temperatures drop, the leaves of these evergreen shrubs frequently droop and curl up like green cigars. These leaf movements do seem to be tied to the weather but their triggers and function have been the source of a lot of debate. Certainly not all Rhododendrons are cold hardy but those that are seem to benefit from reorienting their leaves. Why does this happen?

In the past it has been suggested that leaf reorientation may have something to do with reducing snow load. If the leaves were to remain horizontal, this could cause enough snow buildup to break branches. The fact that a considerable amount of ice and snow can accumulate on branches regardless of leaf position, and largely without harm, seems to suggest that this is not the case. Others have suggested that it could be a way to reduce water loss. As the leaves droop and curl, they are hypothetically increasing the humidity around their leaves and thus reducing their chances of desiccation.

Photo by Nicholas A. Tonelli licensed under CC BY 2.0

This seems pretty far fetched for a few reasons. For starters, Rhododendron simply do not open their stomata during the colder months. By keeping them closed, there is no net transfer of water into or out of the leaves. Also, their thick, waxy cuticle keeps water within the leaves from evaporating out as well. Finally, leaf drooping and curling happens long before the ground freezes and therefore doesn't seem to be triggered by a lack of water in the environment.

The leading theories on this phenomenon seem to deal more with issues at the cellular level. The first of these has to do with the sensitive photosynthetic machinery inside the chloroplasts. Leaf drooping may actually be a response to increased light. Though we generally don't think about photosynthesis in the winter months, evergreen plants actually experience the highest light intensities of the year during this time period. Throughout the growing season, they are generally shaded by the overstory. However, once the canopy leaves fall, things change.

Because the plants are, for the most part dormant, the photosystems within the chloroplasts have no way of dissipating the energy from the incoming sunlight. Photosystem II is especially vulnerable under such scenarios. Experiments have shown that leaves that were forced to stay horizontal during the winter experienced permanent sun damage and photosynthesized considerably less than leaves that were allowed to droop once favorable temperatures returned. The thought is that by positioning the leaves vertically, the plants are reducing the amount of direct light hitting them throughout winter and therefore reducing the potential for light damage.

Photo by Lorianne DiSabato licensed under CC BY-NC-ND 2.0

These experiments also revealed something else about the changes in leaf position when it comes to shape. As it turns out, curling made no difference in protecting the leaves from light damage. It would seem that drooping and curling are responses to two different types of environmental stress. So, why do the leaves curl?

The answer to this question is physical and one that has gained a lot of research attention in the field of cryogenics. When living tissues freeze, ice crystals build up to the point that they can rupture cell membranes. This is only exacerbated if the tissues thaw out quickly. Anyone that has ever tried to freeze and then thaw leafy vegetables knows what I am talking about.

To best preserve tissues via freezing, they must freeze quickly, which reduces the size of the ice crystals that can form, and then thaw out slowly. Researchers found that Rhododendron leaves freeze completely at temperatures below -8 degrees Celsius (17.6 degrees Fahrenheit), temperatures that occur regularly throughout the range of temperate Rhodo species. Again, experiments were able to demonstrate that flat leaves thaw much more rapidly than curled leaves. This is because a curled leaf exposes far less surface area to the warming sun than does a flat leaf. As such, curled leaves don't thaw out as fast and thus are able to avoid much of the damaging effects of daily freeze-thaw cycles.

Though these are all components of the Rhodo leaf puzzle, there is still much work to be done. What we do know is that leaf drooping and leaf curling are two separate behaviors responding to different environmental pressures. Indeed, it appears that these two traits seem to be tied to cold hardiness in the genus Rhododendron. What the exact triggers are and how they produce the changes in shape and orientation, as well as the mechanics of winter survival at the cellular level are topics that are going to require further study. Until then, I think its safe to say that we can appreciate and, to some degree, rely on the spot forecasting abilities of these wonderful shrubs.

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

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

The Other Balsaminaceae

[SOURCE]

Have you heard of Hydrocera triflora? I hadn't until just recently. To my surprise, Hydocera is one of only two genera that make up the family Balsaminaceae. What's more, it is a monotypic genus, with this lovely species being the single representative. There is no question that H. triflora has been completely overshadowed by its cousins, the Impatiens. In fact, literature on this species is quite scant across the board.

The first question you may be asking is what differentiates Hydrocera from the Impatiens? The differences are rather subtle. I don't know if I would have considered this plant unique enough to warrant its own genus, however, closer botanical observations tell a more nuanced story. The biggest differences between Hydrocera and Impatiens has to do with flower and fruit morphology.

Photo by Lalithamba licensed under CC BY 2.0

For starters, the flowers of Hydrocera consist of a full compliment of 5 sepals and 5 petals. The petals themselves are all free from one another. Contrast this with Impatiens, whose flowers mostly consist of 3 sepals and 4 petals that are fused into pairs. The second major difference lies in the fruits. Many of us will be familiar with the explosive capsules of the various Impatiens species, each of which contains many seeds. Hydrocera on the other hand, produces berries that contain 5 seeds. Such vastly different developmental pathways in reproductive structures appear to be enough to warrant the taxonomic separation between the two genera.

The next question one might asking is why are Impatiens so diverse while Hydrocera contains only a single species? This is anyone's guess, really, but there has been at least a few hypotheses put forward that sound plausible. One has to do with habitat preference. Impatiens are largely plants of upland forests and montane environments. Such habitats may offer more potential for diversification due to high heterogeneity in resources and lots of potential for isolation of various populations. Contrast this with the habitat of H. triflora. Though it occurs throughout a wide swath of lowland Asia and India, it is semi-aquatic and these types of habitats may be more restrictive for diversification.

[SOURCE]

Another possibility has to do with seed dispersal. As mentioned above, Impatiens produce lots of seeds per capsule and, with their explosive habit, can disperse them over relatively large distances. Contrast this with Hydrocera. When the berries mature, they fall into the water and sink. They remain submerged until rot or various aquatic organisms eat away at the fleshy coating. Once the seeds have been freed, air sacs cause them to float on the currents until seasonal drying brings them back into contact with the mud. Though this is certainly an effective method for dispersal, the lower seed production rate coupled with being at the mercy of the currents means that Hydrocera is probably considerably less likely to find itself in new habitats.

Again, this is largely speculation at this point. We simply don't know enough about this oddball of the balsam world to make any serious conclusions. Luckily H. triflora is not a species under immediate threat. It seems to do quite well throughout its range, frequently occurring in flooded ditches and rice patties. Still, such stories underlie the importance of fostering and funding organism-focused research.

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

Further Reading: [1] [2]

Dipterocarp Forests

Photo by michel candel licensed under CC BY-NC-SA 2.0

Spend any amount of time reading about tropical forests and you are destined to come across mention of dipterocarp forests. If you're anything like me, your initial thought might have been something along the lines of "what the heck does that mean?" Does it describe some sort of structural aspect of the forest, or perhaps a climatic component? To my surprise, dipterocarp forests refer to any forest in which the dominant species of trees are members of the family Dipterocarpaceae. Thus, I was introduced to a group of plants entirely new to me!

The family Dipterocarpaceae comprises 16 genera and roughly 700 species. Its members can be found throughout the tropical regions of the world, though they hit their greatest numbers in the forests of southeast Asia and specifically Borneo. As far as habit is concerned, the dipterocarps are largely arborescent, ranging in size from intermediate shrubs to towering, emergent canopy trees. If you have watched a documentary on or been to a tropical forest, it is very likely that you have seen at least one species of dipterocarp.

Photo by Mike Prince licensed under CC BY 2.0

The dipterocarps have a long evolutionary history that stretches back to the supercontinent of Gondwana. As this massive landmass proceeded to break apart, the early ancestors of this group were carried along with them. Today we can find members of this family in tropical regions of South America, Africa, and Asia. Taxonomically speaking, the family is further divided into three sub families that, to some degree, reflect this distribution.  The subfamily Monotoideae is found in Africa and Colombia, the subfamily Pakaraimoideae is found in Guyana, and the subfamily Dipterocarpoideae is found in Asia.

Biologically, the dipterocarps are quite fascinating. Some species can grow quite large. Three genera - Dryobalanops, Hopea, and Shorea - regularly produce trees of over 80 meters (260 feet) in height. The world record for dipterocarps belongs to an individual of Shorea faguetiana, which stands a whopping 93 meters (305 feet) tall! That's not to say all species are giants. Many dipterocarps live out their entire lives in the forest understory.

Dipterocarpus retusus. Public Domain

For species growing in seasonal environments, flowering occurs annually or nearly so. Also, for dipterocarps that experience regular dry seasons, deciduousness is a common trait. For those growing in non-seasonal environments, however, flowering is more irregular and leaves are largely evergreen. Some species will flower once every 3 to 5 years whereas others will flower once every decade or so. In such cases, flowering occurs en masse, with entire swaths of forest bursting into bloom all at once. These mast years often lead to similar aged trees that all established in the same year. Though more work needs to be done on this, it is thought that various bee species comprise the bulk of the dipterocarp pollinator guild. 

Ecologically speaking, one simply cannot overstate the importance of this family. Wherever they occur, dipterocarps often form the backbone of the forest ecosystem. Their number and biomass alone is worth noting, however, these trees also provide fruits, pollen, nectar, and habitat for myriad forms of life. The larger dipterocarps are often considered climax species, meaning that they dominate in regions made up of mostly primary forest. For the most part, these trees are able to take advantage of more successional habitats, however, this has been shown to be severely limited by the availability of localized seed sources. 

Since we are on the topic of regeneration, a conversation about dipterocarps would not be complete if we didn't touch on logging. These trees are massive components of tropical economies. Their wood is highly coveted for a a variety of uses I won't go into here. The point is that, on a global scale, dipterocarp forests have taken a huge hit. Many species within this family are now threatened with extinction. Logging, both legal and illegal, specifically aimed at dipterocarps, has seen the destruction of millions of acres of old growth dipterocarp forests. With them goes all of the life that they support.

It's not enough to protect individual species. We need to rally behind whole ecosystem protection. Without it, we literally have nothing. Luckily there are groups like the Center For International Forestry Research and the Forest Research Institute of Malaysia that are working hard on research, conservation, and improved forestry standards in an effort to ease up on the detrimental practices currently in place. Still, these efforts are not enough either. Without the care, concern, and most important, the funding from folks like us, little can be done to stop the tide. That is why supporting land conservation agencies is one of the most powerful things we can do for this planet and for each other. 

Some great land conservation organizations worth supporting:

The Rainforest Trust - https://www.rainforesttrust.org/

The Nature Conservancy - http://bit.ly/2B0hFm

The Rainforest Alliance - https://www.rainforest-alliance.org/

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

urther Reading: [1]

Everlasting or Seven Years Little

Photo by Andrew massyn licensed under CC BY-SA 3.0

Common names are a funny thing. Depending on the region, the use, and the culture, one plant can take on many names. In other situations, many different plants can take on a single name. Though it isn't always obvious to those unfamiliar with them, the use of scientific names alleviates these issues by standardizing the naming of things so that anyone, regardless of where they are, knows what they are referring to. That being said, sometimes common names can be entertaining.

Take for instance, plants in the genus Syncarpha. These stunning members of the family Asteraceae are endemic to the fynbos region of the Eastern and Western Cape of South Africa. In appearance they are impossible to miss. In growth habit they have been described as "woody shrublets," forming dense clusters of woody stems covered in a coat of woolly hairs. Sitting atop their meter-high stems are the flower heads.

Each flower head consists of rings of colorful paper-like bracts surrounding a dense cluster of disk flowers. The flowering period of the various species can last for weeks and spans from October, well into January. Numerous beetles can be observed visiting the flowers and often times mating as they feed on pollen. Some of the beetles can be hard to spot as they camouflage quite well atop the central disk. Some authors feel that such beetles are the main pollinators for many species within this genus.

Photo by JonRichfield licensed under CC BY-SA 3.0

Their mesmerizing floral displays are where their English common name of "everlasting" comes from. Due to the fact that they maintain their shape and color for a long time after being cut and dried, various Syncarpha species have been used quite a bit in the cut flower industry. A name that suggests everlasting longevity stands in stark contrast to their other common name. 

These plants are referred to as "sewejaartjie" in Afrikaans, which roughly translates to "seven years little." Why would these plants be referred to as everlasting by some and relatively ephemeral by others? It turns out, sewejaartjie is a name that has more to do with their ecology than it does their use in the floral industry.

As a whole, the 29 described species of Syncarpha are considered fire ephemerals. The fynbos is known for its fire regime and the plants that call this region home have evolved in response to this fact. Syncarpha are no exception. They flower regularly and produce copious amounts of seed but rarely live for more than 7 years after germination. Also, they do not compete well with any vegetation that is capable of shading them out.

Photo by Andrew massyn licensed under CC BY-SA 3.0

Instead, Syncarpha invest heavily in seed banking. Seeds can lie dormant in the soil for many years until fires clear the landscape of competing vegetation and release valuable nutrients into the soil. Only then will the seeds germinate. As such, the mature plants don't bother trying to survive intense ground fires. They burn up along with their neighbors, leaving plenty of seed to usher in the next generation.

Research has shown that its not the heat so much as the smoke that breaks seed dormancy in these plants. In fact, numerous experiments using liquid smoke have demonstrated that the seeds are likely triggered by some bio-active chemical within the smoke itself.

So, there you have it. Roughly 29 plants with two common names, each referring back to an interesting aspect of the biology of these plants. Despite their familiarity and relative ease of committing to memory, the common names of various species only get us so far. That's not to say we should abolish the use of common names altogether. Learning about any plant should be an all encompassing endeavor provided you know which plant you are referring to.

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

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

The Incredible Feat of a Resurrection Plant

By EnigmaticMindX via https://imgur.com/4Pa9zdN

It is understandable why one would look at the crispy brown bundle of a Selaginella lepidophylla and think that it was dead. No wonder then why this hardy spikemoss has become such a novelty item for those looking for a unique gift. Indeed, even the common name of "resurrection plant" suggests that this species miraculously returns from the dead with the simple addition of water. A dormant resurrection plant is far from dead, however. It is in a state of dormancy that we are still struggling to understand.

Selaginella lepidophylla is native to the Chihuahuan desert, spanning the border between the US and Mexico. This is a harsh habitat for most plants, let alone a Lycophyte. However, this lineage has not survived hundreds of millions of years by being overly sensitive to environmental change and S. lepidophylla is a wonderful reminder of that.

As you can probably imagine, tolerating near-complete desiccation can be pretty beneficial when your habitat receives an average of only 235 mm (9.3 in) of rain each year. A plant can either store water for those lean times or go dormant until the rains return. The latter is exactly what S. lepidophylla does. As its water supply dwindles, the whole body of the plant curls up into a tight ball and waits. With little in the way of roots anchoring it to the ground, dormant plants are often at the mercy of the winds, which blows them around like a tiny tumbleweed until they are wedged into a crack or crevice.

Photo by Gary Nored licensed under CC BY-NC 2.0

When the rains return, S. lepidophylla needs to be ready. Wet this crispy bundle and watch as over the course of about a day, the dormant ball unfurls to reveal the stunning body of a photosynthetic spikemoss ready to take advantage of moist conditions. Such conditions are short lived, of course, so after a few days drying out, the plant shrivels up and returns to its dormant, ball-like state. How does the plant manage to do this? Why doesn't it simply die? The answer to these questions has been the subject of quite a bit of debate and investigation. 

What we do know is that part of its success has to do with curling up into a ball. Without water in its tissues, its sensitive photosynthetic machinery would easily become damaged by punishing UV rays. By curling up, the plant essentially shelters these tissues from the sun. Indeed, plants that were kept from curling up experienced irreversible damage to their photo systems and were not as healthy as plants that did curl up. To this, the plant owes its success to rather flexible cell walls. Unlike other plants that snap when folded, the cells of S. lepidophylla are able to fold and unfold without any major structural damage.

As far as metabolism and chemistry is concerned, however, we are still trying to figure out how S. lepidophylla survives such drastic shifts. For a while it was thought that, similar to other organisms that undergo such dramatic desiccation, the plant relies on a special sugar called trehalose. Trehalose is known to bind to important proteins and membranes in other desiccation-tolerant organisms, thus protecting them from damage and allowing them to quickly return to their normal function as soon as water returns.

An analysis of non-desiccating Selaginella species, however, showed that S. lepidophylla doesn't produce a lot of trehalose. Though it is certainly present in its tissues, more wet-loving species of Selaginella contain much higher amounts of this sugar. Instead, it has been found that other sugars may actually be playing a bigger role in protecting the inner workings of this plant. Sorbitol and xylitol are found in much higher concentrations within the tissues of S. lepidophylla, suggesting that they may be playing a bigger role than we ever realized. More work is needed to say for sure.

Finally, it would appear that S. lepidophylla is able to maintain enzyme activities within its cells at much higher levels during desiccation periods than was initially thought possible. When dried, some enzymes were found to be working at upwards of 75% efficiency of those found in hydrated tissues. This is really important for a plant that needs to respond quickly to take advantage of fleeting conditions. Along with quick production of new enzymes, this "idling" of enzymatic activity during dormancy is thought to not only protect the plant from too much respiration, but also allows it to hit the ground running as soon as favorable conditions return. 

Despite our lack of understanding of the process, it is amazing to watch this resurrection plant in action. To see something go from a death-like state to a living, photosynthetic organism over the course of a day is truly a marvel worth enjoying.

Photo Credits: [1] [2]

Further Reading: [1]

Cockroaches & Unexpected Partnerships

Photo by Alpsdake licensed under CC BY-SA 4.0

Say "cockroach" and most people will start to squirm. These indefatigable insects are maligned the world over because of a handful of species that have settled in quite nicely among human habitats. The world of cockroaches is far more diverse than most even care to realize, and where they occur naturally, these insects provide important ecological services. For instance, over the last decade or so, researchers have added pollination and seed dispersal to the list of cockroach activities. 

That's right, pollination and seed dispersal. It may seem odd to think of roaches partaking in such interactions but a study published in 2008 provides some of the first evidence that roaches are doing more with plants than eating their decaying tissues. After describing a new species of Clusia in French Guiana, researchers set out to investigate what, if anything, was pollinating it. The plant was named Clusia sellowiana and its flowers emitted a strange scent. 

Cockroach pollinating C. sellowiana. [SOURCE]

The source of this scent was the chemical acetoin. It seemed to be a rather attractive scent as a small variety of insects were observed visiting the flowers. However, only one insect seemed to be performing the bulk of pollination services for this new species - a small cockroach called Amazonia platystylata. It turns out that the roaches are particularly sensitive to acetoin and although they don't have any specific anatomical features for transferring pollen, their rough exoskeleton nonetheless picks up and deposits ample amounts of the stuff. 

It would appear that C. sellowiana has entered into a rather specific relationship with this species of cockroach. Although this is only the second documentation of roach pollination, it certainly suggests that more attention is needed. This Clusia isn't alone in its interactions with cockroaches either. As I hinted above, roaches can now be added to the list of seed dispersers of a small parasitic plant native to Japan. 

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 (A) M. humile fruit showing many minute seeds embedded in the less juicy pulp. (B) Fallen fruits. (C) Blattella nipponica feeding on the fruit. (D) Cockroach poop with seeds. (E) Stained cockroach-ingested seeds. [SOURCE]

Monotropastrum humile looks a lot like Monotropa found growing in North America. Indeed, these plants are close cousins, united under the family Ericaceae. Interestingly enough, it was only recently found that camel crickets are playing an important role in the seed dispersal of this species. However, it looks like they aren't the only game in town. Researchers have also found that a forest dwelling cockroach called Blattella nipponica serves as a seed disperser as well. 

The roaches were observed feeding on the fruits of this parasitic plant, consuming pulp and seed alike. What's more, careful observation of their poop revealed that seeds of M. humile passed through the digestive tract unharmed. Cockroaches can travel great distances and therefore may provide an important service in distributing the seeds of a rather obscure parasitic plant. To think that this is an isolated case seems a bit naive. It seems to me like we should pay a little more attention to what cockroaches are doing in forests around the world. 

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

Further Reading: [1] [2]

Are Crickets Dispersing Seeds of Parasitic Plants?

[SOURCE]

Parasitic plants lead unique lifestyles. Many have foregone photosynthesis entirely by living off fungi or their photosynthetic neighbors. Indeed, there are many anatomical and physiological adaptations that are associated with making a living parasitically. Whether they are full parasites or only partial, one thing that many parasitic plants have in common are tiny, dust-like seeds. Their reduced size and thin seed coats are generally associated with wind dispersal, however, there are always exceptions to the rule. Recent evidence has demonstrated that a handful of parasitic plants have evolved in response to a unique seed dispersal agent - camel crickets.

A research team based out of Japan recently published a paper describing a rather intriguing seed dispersal situation involving three species of parasitic plants (Yoania amagiensis - Orchidaceae, Monotropastrum humile - Ericaceae, and Phacellanthus tubiflorus - Orobanchaceae). These are all small, achlorophyllous herbs that either parasitize trees directly through their roots or they parasitize the mycorrhizal fungi associated with said trees. What's more, each of these species are largely inhabitants of the dense, shaded understory of rich forests.

These sorts of habitats don't lend well to wind dispersal. The closed forest canopy and dense understory really limits wind flow. It would appear that these three plant species have found away around this issue. Each of these plants invest in surprisingly fleshy fruits for their parasitic lifestyle. Also, their seeds aren't as dust-like as many of their relatives. They are actually very fleshy. This is odd considering the thin margins many parasitic plants live on. Any sort of investment in costly tissues must have considerable benefits for the plants if they are to successfully get their genes into the next generation.

Fleshy fruits like this are usually associated with a form of animal dispersal called endozoochory. Anyone that has ever found seed-laden bird poop understands how this process works. Still, simply getting an animal to eat your seeds isn't necessarily enough for successful dispersal. Seeds must survive their trip through the gut and come out the other end relatively in tact for the process to work. That is where a bit of close observation came into play.

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[SOURCE]

After hours of observation, the team found that the usual frugivorous suspects such as birds and small mammals showed little to no interest in the fruits of these parasites. Beetles were observed munching on the fruits a bit but the real attention was given by a group of stumpy-looking nocturnal insects collectively referred to as camel crickets. Again, eating the fruits is but one step in the process of successful seed dispersal. The real question was whether or not the seeds of these parasites survived their time inside either of these insect groups. To answer this question, the team employed feeding trials.

They compared seed viability by offering up fruits to beetles and crickets both in the field and back in the lab. Whereas both groups of insects readily consumed the fruits and seeds, only the crickets appeared to offer the greatest chances of a seed surviving the process. Beetles never pooped out viable seeds. The strong mandibles of the beetles fatally damaged the seeds. This was not the case for the camel crickets. Instead, these nocturnal insects frequently pooped out tens to hundreds of healthy, viable seeds. Considering the distances the crickets can travel as well as their propensity for enjoying similar habitats as the plants, this stacks up to potentially be a beneficial interaction. 

The authors are sure to note that these results do not suggest that camel crickets are the sole seed dispersal agents for these plants. Still, the fact that they are effective at moving large amounts of seeds is tantalizing to say the least. Taken together with other evidence such as the fact that the fruits of these plants often give off a fermented odor, which is known to attract camel crickets, the fleshy nature of their fruits and seeds, and the fact that these plants present ripe seed capsules at or near the soil surface suggests that crickets (and potentially other insects) may very well be important factors in the reproductive ecology of these plants.

Coupled with previous evidence of cricket seed dispersal, it would appear that this sort of relationship between plants and crickets is more widespread than we ever imagined. It is interesting to note that relatives of both the plants in this study and the camel crickets occur in both temperate and tropical habitats around the globe. We very well could be overlooking a considerable component of seed dispersal ecology via crickets. Certainly more work is needed.

Photo Credits: [1]

Further Reading: [1] [2]

The Elusive White Walnut

Today we go in search of the elusive white walnut (Juglans cinerea). Many of you may know it by its other common name - the butternut. Sadly, being able to find large, mature specimens of this wonderful tree is getting harder and harder. Watch and find out why...

Music by:
Artist: Somali Yacht Club
Track: Loom
https://somaliyachtclub.bandcamp.com/