Deer Skew Jack-in-the-Pulpit Sex Ratios

Photo by Michael Janke licensed under CC BY-ND 2.0.

Deer populations in North America are higher than they have been at any point in history. Their explosion in numbers not only leads to series health issues like starvation and chronic wasting disease, it has also had serious impacts on regional plant diversity. Wherever hungry herds of deer go, plants disappear from the landscape. However, the impacts of deer on plants aren’t limited to species they can eat. Research on Jack-in-the-Pulpit (Arisaema triphyllum) has shown that deer can have plenty of surprising indirect impacts on plants as well.

Though I wouldn’t put anything past a hungry deer, plants like Jack-in-the-Pulpit aren’t usually on the menu for these ungulates. Their leaves, stems, and flowers are chock full of raphide crystals that will burn the mouths and esophagus of most herbivores. Still, this doesn’t mean deer aren’t impacting these plants in other ways. Because deer are congregating in high abundance in our ever-shrinking natural spaces, they are having serious impacts on local growing conditions. Wherever deer herds are at high numbers, forests are experiencing soil compaction, soil erosion, and a disappearance of soil leaf litter (also due in part to invasive earthworms). Thanks to issues like these, plants like Jack-in-the-Pulpit are undergoing some serious changes.

Like many aroids, sex expression in the genus Arisaema is fluid and relies on energy stores. Smaller plants store less energy and tend to only produce male flowers when they bloom. Pollen, after all, is cheap compared to eggs and fruit. Only when a plant has stored enough energy over the years will it begin to produce female flowers in addition to males and only the largest, most robust plants will switch over entirely to female flowers. As you can imagine, the ability of a plant to acquire and store enough energy is dependent on the quality of the habitat in which it grows. This is where deer enter into the equation.

High densities of deer inevitably cause serious declines in habitat quality of plants like Jack-in-the-Pulpit. As leaf litter disappears and soil compaction grows more severe, individual plants have a much harder time storing enough energy each growing season. In places where deer impacts are heaviest, the sex ratios of Jack-in-the-Pulpit populations begin to skew heavily towards males because individual plants must grow much longer before they can store enough energy to produce female flowers. It doesn’t end there either. Not only does it take longer for a plant to begin producing female flowers, individual plants must also reach a much larger size in order to produce female flowers than in areas with fewer deer.

Photo by Charles de Mille-Isles licensed under CC BY-ND 2.0.

As mentioned, seed production takes a lot of energy and any plant that is able to produce viable fruits will have less energy stores going into the next season. This means that even if a plant is able to produce female flowers and successfully set seed, they will have burned through so much energy that they will likely revert right back to producing only male flowers the following year, further skewing the sex ratios of any given population towards males. Interestingly, this often results in more individuals being produced via clonal offshoots. The more clones there are in a population, the less diverse the gene pool of that population becomes.

Without actually eating the plants, deer are having serious impacts on Jack-in-the-Pulpit population dynamics. I am certain that this species isn’t alone either. At least Jack-in-the-Pulpit is somewhat flexible in its reproductive behaviors. Other plants aren’t so lucky. I realize deer are a hot button issue but there is no getting around the fact that our mismanagement of their natural predators, habitat, and numbers are having serious and detrimental impacts on wild spaces and all the species they support.

Photo Credits: [1] [2]

Further Reading: [1]

The Fungus-Mimicking Mouse Plant

The mouse plant (Arisarum proboscideum) is, to me, one of the most charming aroids in existence. Its small stature and unique inflorescence are a joy to observe. It is no wonder that this species has attained a level of popularity among those of us who enjoy growing oddball plants. Its unique appearance may be reason enough to appreciate this little aroid but its pollination strategy is sure to seal the deal.

The mouse plant is native to shaded woodlands in parts of Italy and Spain. It is a spring bloomer, hitting peak flowering around April. It has earned the name “mouse plant” thanks to the long, tail-like appendage that forms at the end of the spathe. That “tail” is the only part of the inflorescence that sticks up above the arrow-shaped leaves. The rest of the structure is presented down near ground level. From its stature and position, to its color, texture, and even smell, everything about the inflorescence is geared around fungal mimicry.

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The mouse plant is pollinated by fungus gnats. However, it doesn’t offer them any rewards. Instead, it has evolved a deceptive pollination syndrome that takes advantage of a need that all living things strive to attain - reproduction. To draw fungus gnats in, the mouse plant inflorescence produces compounds that are said to smell like fungi. Lured by the scent, the insects utilize the tail-like projection of the spathe as a sort of highway that leads them to the source.

Once the fungus gnats locate the inflorescence, they are presented with something incredibly mushroom-like in color and appearance. The only opening in the protective spathe surrounding the spadix and flowers is a tiny, dark hole that opens downward towards the ground. This is akin to what a fungus-loving insect would come to expect from a tiny mushroom cap. Upon entering, the fungus gnats are greeted with the tip of the spadix, which has come to resemble the texture and microclimate of the underside of a mushroom.

Anatomy of a mouse plant inflorescence [SOURCE]

This is exactly what the fungus gnats are looking for. After a round of courtship and mating, the fungus gnats set to work laying eggs on the tip of the spadix. Apparently the tactile cues are so similar to that of a mushroom that the fungus gnats simply don’t realize that they are falling victim to a ruse. Upon hatching, the fungus gnat larvae will not be greeted with a mushroomy meal. Instead, they will starve and die within the wilting inflorescence. The job of the adult fungus gnats is not over at this point. To achieve pollination, the plant must trick them into contacting the flowers themselves.

Both male and female flowers are located down at the base of the structure. As you can see in the pictures, the inflorescence is two-toned - dark brown on top and translucent white on the bottom. The flowers just so happen to sit nicely within the part of the spathe that is white in coloration. In making a bid to escape post-mating, the fungus gnats crawl/fly towards the light. However, because the opening in the spathe points downward, the lighted portion of the structure is down at the bottom with the flowers.

The leaves are the best way to locate these plants. Photo by Meneerke bloem licensed under CC BY-SA 4.0

Confused by this, the fungus gnats dive deeper into the inflorescence and that is when they come into contact with the flowers. Male and female flowers of the mouse plants mature at the exact same time. That way, if visiting fungus gnats happen to be carrying pollen from a previous encounter, they will deposit it on the female flowers and pick up pollen from the male flowers all at once. It has been noted that very few fungus gnats have ever been observed within the flower at any given time so it stands to reason that with a little extra effort, they are able to escape and with any luck (for the plant at least) will repeat the process again with neighboring individuals.

The mouse plant does not appear to be self-fertile so only pollen from unrelated individuals will successfully pollinate the female flowers. This can be a bit of an issue thanks to the fact that plants also reproduce vegetatively. Large mouse plant populations are often made up of clones of a single individual. This may be why rates of sexual reproduction in the wild are often as low as 10 - 20%. Still, it must work some of the time otherwise how would such a sophisticated form of pollination syndrome evolve in the first place.

Photo Credit: [1] [2] [3]

Further Reading: [1] [2]

The Intriguing Pollination of a Central American Anthurium

As an avid gardener of both indoors and out, there are few better experiences than getting to see familiar plants growing in the wild for the first time. That experience is made all the better when you find out new and interesting facts about their ecology. On a recent trip to Costa Rica, I was introduced to a wide variety of Anthurium species. I marveled at how amazing these plants look in situ and was taken aback to learn that many produce flowers with intoxicating aromas.

I was also extremely fortunate to be in the presence of some aroid experts during this trip and their knowledge fueled my interest in getting up close and personal with what little time I had with these plants. They were able to ID the plants and introduce me to their biology. One species in particular has been the subject of interest in an ongoing pollination study that has proven to be unique.

The plant in question is known scientifically as Anthurium acutifolium and it is rather charming once you get to know it. It is a terrestrial plant with relatively large leaves for its overall size. Its range includes portions of lowland Costa Rica and Panama. Its flowers are typical of what one would expect out of this family. They are fused into a type of inflorescence known as a spadix and can range in color from white to green and occasionally red. If you are lucky to visit the spadix between roughly 8:00 AM and 12:30 PM, you may notice a rich scent that, to me, is impossible to describe in words.

It's this scent that sets the stage for pollination in this species. During some down time, University of Vienna grad student Florian Etl discovered that the spadix of A. acutifolium was getting a lot of attention from a particular species of small bee. Closer inspection revealed that they were all males of a species of oil-collecting bee known as Paratetrapedia chocoensis. Now, the females of these oil collecting bees are well known in the pollination literature. They visit flowers that secrete special oils that the females then use to build nests and feed their young. This is why the attention from male bees was so intriguing.

A: A male P. chocoensis bee approaching a scented spadix of an inflorescence of A. acutifolium. B: The abdominal mopping behavior of male P. chocoensis oil bees on a spadix. C: Ventral side of the abdomen of a male P.chocoensis covered with pollen. D: A male P. chocoensis bee on a spadix of an inflorescence of A. acutifolium, touching the pollen shedding anthers. E: Pubescent region pressed on the surface of A. acutifolium during the mopping behavior. F: A scented inflorescence of A. acutifolium with three male P. chocoensis individuals. G: Image of the abdomen of a male P.chocensis in lateral view showing the conspicuous pubescent region. (SOURCE)

Males would land on the spadix and begin rubbing the bottom of their abdomen along its surface. In doing so, they inevitably picked up and deposited pollen. To date, such behavior was unknown among male oil bees. What exactly were these male bees up to?

As it turns out, the males were collecting fragrances. Close inspection of their morphology revealed that each male has a small patch of dense hairs underneath their abdomen. The males are definitely not after fatty oils or nectar as A. acutifolium does not secrete either of these substances. Instead, it would appear that the male oil bees are there to collect scent, which is mopped up by that dense patch of hairs. Even more remarkable is the fact that in order to properly collect these fragrance compounds, the bees are likely using solvents that they have collected from other flowering plant species around the forest.

What they are doing with these scent compounds remains a mystery but some potential clues lie in another scent/pollination system. Male orchid bees perform similar scent-collecting activities in order to procure unique scent bouquets. Though the exact function of their scent collecting is not known either, we do know that these scents are used in the process of finding and procuring mates. It is likely that these male oil bees are using them in a similar way.

Taken together, these data suggest that a very specific pollination syndrome involving A. acutifolium and male oil bees has evolved in Central American forests. No other insects were observed visiting the flowers of A. acutifolium and the scents only ever attracted males of these specific oil bees during the hours in which the spadix was actively producing the compounds. This is a remarkable pollination syndrome and one that encourages us to start looking elsewhere in the forest. This, my friends, is why there is no substitute for simply taking the time to observe nature. We must take the time to get outside and poke around because we stand to miss out on so much of what makes our world tick and without such knowledge, we risk losing so much. 

Photo Credits: Florian Etl [1]

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] 

Arums, Orchids and Vines, Oh My!

This week we head into the forests of Illinois to see what late spring botany we can find. This is one of the coolest times of the year to look for plants in temperate North America. 

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