Alligators Increase Plant Diversity

Photo by mbarisson licensed under CC BY-ND 2.0.

When you think of gardening, alligators don’t readily jump to mind. Hang out long enough in places like the Everglades and that might change. I was only recently introduced to the concept of a “gator hole” and I must say, I was surprised what a quick search of the literature revealed. It turns out that alligators are important ecosystem engineers and do a wonderful job at increasing plant diversity in the wetlands they inhabit.

Throughout southeastern North America, gators change their behaviors with the seasons. During the rainy season, alligators can be found floating in open water or sunning themselves on land. Except when hunting, they don’t seem to do anything with much urgency. Their activity level changes during the dry season when water is in short supply. Gators don’t sit back and let nature take its course. They spring into action and create their own aquatic refuges.

As the surrounding landscape begins to dry, gators will excavate holes or pits in the soggy ground called gator holes. These holes hold onto water when most of the surrounding landscape isn’t. The process of digging a gator hole may seem destructive but it all must be placed in the context of the surrounding environment. Most gator habitat exists in low lying areas. In places like the Everglades, there isn’t much topography to speak of. When a gator excavates a gator hole, it creates variation in both hydrology and soil conditions.

Photo by Anita Gould licensed under CC BY-ND 2.0.

Soils that have built up over time are lifted out of the hole and piled into mounds. Mounded soils are not only rich in nutrients, they also dry at different rates, creating a gradient in water availability. Plants that normally can’t germinate and grow in saturated soils find suitable spots to live up on the soil mounds while emergent aquatic vegetation fills in along the parameter. Plants that normally prefer to grow in deeper water can also establish within the gator hole itself. In the midst of fairly uniform marsh vegetation, a gator hole quickly becomes a hotbed of plant diversity. The differences in vegetation can be so stark compared to the surrounding landscape that some scientists can actually map gator holes using aerial scans simply by measuring the differences in infrared radiation given off by the leaves of all the different plants that establish around them.

Of course, all of that plant diversity has a huge effect on other organisms as well. Gator holes become important areas for various reptiles, amphibians, birds, and so much more. The paths that alligators take to and from their holes even act like fire breaks, changing the way fire moves through the landscape, which only increases the heterogeneity of the immediate area. Fish, though occasionally eaten, greatly benefit from the stability of water levels within a gator hole. All in all, gator holes are extremely important habitats. Not only do they support a high diversity of plants and animals alike, they make places like the Everglades even more dynamic than they already are.

Photo Credits: [1] [2]

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

The Deceptive Ways of the Calypso Orchid

Photo by Murray Foubister licensed under CC BY-ND 2.0.

Behold the Calypso orchid, Calypso bulbosa. This circumboreal orchid exists as a single leaf lying among the litter of dense conifer forests. They go virtually unnoticed for most of the year until it comes time to flower.

In early spring, the extravagant blooms open up and await the arrival of bumblebees. Calypsos go to great lengths to attract bumblebees. The flower is said to have a sweet scent. Also, the lip sports small, yellow, hair-like protrusions that are believed to mimic anthers covered in pollen. Finally, within the pouch formed by the lip are two false nectar spurs. All of these are a ruse. The Calypso offers no actual rewards to visiting bumblebees.

Not just any bumblebee will do. For the ruse to work, it requires freshly emerged workers that are naive to the orchid’s deception. Bumblebees are not mindless animals. They quickly learn which flowers are worth visiting and which are not. Because of this, the Calypso has only short window of time in which bumblebees in the vicinity are likely to fall for its tricks. As a result, pollination rates are often very low for this orchid.

The most interesting aspect of all of this is that the so-called "male function" of the flower - pollinia removal - is more likely to occur than the "female function" - pollen deposition. The reason for this makes a lot of sense in context; male function requires a bumblebee to be fooled only once whereas female function requires a bumblebee to be fooled at least twice.

The caveat to all of this deception is that a single Calypso, like all other orchids, can produce tens of thousands of seeds. Each orchid therefore has tens of thousands of potential propagules to replace itself in the next generation. Despite that fact, the Calypso orchid is on the decline. Habitat destruction, poaching, deer, and invasive species are taking their toll. If you care about orchids like the Calypso, please consider supporting organizations like the North American Orchid Conservation Center.

Photo by Murray Foubister licensed under CC BY-ND 2.0.

Photo Credit: [1] [2]

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

Pretty Pantaloons From a Member of the Poppy Family

With delicately dissected foliage and flowers that look like pantaloons, it is hard to believe that Dutchman's breeches (Dicentra cucullaria) are related to the common garden poppy. No matter how incredulous it may seem, they are in fact peculiar members of Papaveraceae. I can't get enough of these lovely spring ephemerals and their beauty is equally matched by their intriguing ecology. This species really is the full package.

At home in mesic deciduous forests, Dutchman's breeches are true spring ephemerals. They are primarily denizens of eastern North America, however, disjunct populations can be found in the Pacific Northwest. These are likely relics of a once wider distribution that was split in two by advancing glaciers during the Pleistocene. Dutchman’s breeches live out their entire lives before the tree canopy closes with a fresh batch of leaves. By mid summer they are little more than dormant bulblets resting below the leaf litter. Like the multitude of spring ephemerals they share the forest with, Dutchman's breeches are vying for pollinators capable of tolerating wide swings in temperature. This is where their peculiar little flowers come in.

Packed away in each spur is a sweet nectary treat. The only insects capable of reaching it are bumblebees (Bombus spp.). With their long tongues, these bees flock to the bright white and yellow flowers with vigor. Aside from the occasional thief who chews a hole at the end of the spur, robust bumblebees have this meal all to themselves. In fact, this relationship is so in sync that nothing else is capable of effectively pollinating the plant.

After a brief flowering period, the plant will set seed. Like many other spring ephemerals, they attach a fleshy structure to their seeds called an elaiosome. This attracts foraging ants in the genus Aphaenogaster, who collect the seeds and take them back to their nests. Once there, the elaiosome is sometimes eaten but mostly the seeds are disposed of in trash middens. In this way, the seeds find a nutrient-rich microclimate safe from seed predators in which to germinate. It is a safe bet that most of the patches you find owe their existence to these industrious little insects.

Further Reading: [1] [2]

Record Breaking Palms

Photo by Vinayaraj licensed under CC BY-ND 2.0.

I like record breaking species. It is always exciting to find out which species produces the largest or smallest of something. Lately (and rightfully so), the titan arum (Amorphophallus titanum) has been getting a lot of attention for its incredible inflorescence. Many have bloomed in botanical gardens over the last few years and each one draws a massive crowd. People flock from far and wide to see that largest unbranched inflorescence in the world. You always see it referred to that way; the largest unbranched inflorescence. That got me to thinking, who produces the largest branched inflorescence in the world?

The answer to this is the talipot palm (Corypha umbraculifera). Native to southern India and Sri Lanka, the talipot palm blows all other branched inflorescences out of the water. Heck, branched or not, looking over its dimensions makes me feel like it puts most floral structures to shame. The branched designation comes from the fact that its flowers aren’t borne on a single stalk but many branching stalks. The proportions of this structure are truly staggering.

A talipot palm topped with a massive white inflorescence. Photo by Cumulus Clouds licensed under CC BY-ND 2.0.

The talipot palm inflorescence can measure upwards of 26 feet (8 m) in length and bear as many as 23.9 million flowers at a time. It has been estimated that if you were to lay out all of the branches and flower stalks end to end, you would have nearly 26,000 feet (8,221 m) of plant material. This is truly epic as far as flowering plants are concerned. Even more amazing is the fact that this epic inflorescence is often produced 65 feet (20 m) up in the air!

As you can imagine, producing such a structure and all of the fruits that result takes an absurd amount of energy. Talipot palms grow for anywhere between 30 and 80 years before blooming. Following pollination, the fruits take another year to mature. Once this job is done, the palm dies. It throws all of its energy into one, truly massive reproductive event. Pretty incredible if you ask me.

During my search, I also came across another interesting record breaking palm, Raphia regalis. This species is native to parts of western Africa where it can be found growing in moist, lowland forests. Raphia regalis has the distinct honor of producing the largest self-supporting leaf in the world. Given what I have read, I would imagine that in a dense forest, it would be extremely difficult to take in the full grandeur of its leaves. They are huge. The current record for a single R. regalis leaf is 82 feet (25.1 m) long. It isn’t a solid leaf but rather a compound leaf made up of much tinnier leaflets. To see one in all of its glory would be a truly special event.

Photos 1911 (above) and 2015 (below) showing the incredible leaf length of Raphia regalis. Photo posted by Dr. Thomas Couvreur and lifted from the book: "from the Congo to the Niger" Vol 2 by A. Schultze

So there you have it. Two incredible plant records held by two incredible palms. Not bad for a quick internet search.

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

Further Reading: [1]

A Shout Out to Western Skunk Cabbage

Photo by Martin Bravenboer licensed under CC BY-ND 2.0.

We all have our biases and one of my biggest botanical bias is that I often think of plants from eastern North America before my mind heads further west. I can’t really fault myself for it because so many of my early plant experiences occurred east of the Mississippi. I want to remedy this a bit today by drawing your attention to a wonderful aroid who frequently gets overshadowed by its eastern cousin.

I am of course talking about western skunk cabbage (Lysichiton americanus). This incredibly beautiful plant enjoys a distribution that ranges from southern Alaska to central California and west into Wyoming and Montana. Like its eastern cousin, western skunk cabbage was awarded its common name thanks to the pungent odor it produces. Its blooming period ranges from March into May depending on where they are growing and the inflorescence is truly something to write home about.

The spadix of western skunk cabbage complete with a tiny rove beetle pollinator. Photo by Walter Siegmund lincensed under CC BY-SA 3.0

Emerging from the base of the plant is a bright yellow structure called a spathe. The spathe envelopes the actual flowering parts, a phallic-looking structure covered in flowers called a spadix. The spadix emits various volatile compounds that function as pollinator attractants. However, whereas many would suggest flies are the preferred pollinator, research indicates that a tiny species of rove beetle called Pelecomalium testaceum takes up the bulk of pollination duties for western skunk cabbage throughout much of its range.

The volatile compounds aren’t there to trick the beetles into thinking they are getting some sort of reward. The plant does actually reward the rove beetles with pollen to eat and relatively safe place to mate. We call these types of signals “honest signals” as they act as an honest calling card that signifies rewards are to be had.

A closer look at a Pelecomalium rove beetle. Not sure which species. Photo by Judy Gallagher licensed under CC BY 2.0

Unfortunately, the beauty of western skunk cabbage has seen it enter into novelty garden collections in other temperate regions of the world. In northern Europe, western skunk cabbage has escaped the confines of the garden and is now considered an invasive species in wetlands of that region. Take care to choose you garden plants wisely. Always plant native plants when the option presents itself.

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

Further Reading: [1] [2]

Why are there so few tree species in Europe?

Photo by Susulyka licensed under CC BY-SA 4.0

Take a look at a list of tree species from temperate Europe, North America, and Asia and you will notice a glaring disparity. Whereas North America and Asia are home to something like 1000 tree species each, Europe is home to just about 500 species. Why is this?

The answer may lie partly in the glacial history of the Northern Hemisphere as well as in some quirks of geology. Starting in the late Pliocene, roughly 3 million years ago, the Earth began to cool. As our planet entered into a epoch dominated by massive, continent-wide glaciers, life was responding accordingly.

Historically it was assumed that Europe lost many of its temperate tree species thanks to the east-west orientation of its mountain ranges. As glaciers advanced from the north, species were pushed farther and farther south until they hit physical barriers in the terrain like the Alps. With nowhere to go but up, many species that couldn’t handle either the rate of climate change or the altitude adjustment simply winked out of existence. Fossil evidence from Europe provides plenty of evidence that this region was once home to far more tree species, including relatives of sweetgum (Liquidambar spp.) and tulip trees (Liriodendron spp.) that are still present in North America, and umbrella pines (Sciadopitys spp.), which still exists in Asia. Many temperate tree species in North America and Asia were spared this fate because there were far fewer barriers to successful southern migrations.

This all sounds a bit too simple and indeed, recent studies suggest that it is. Though climate change, glaciers, and mountains certainly played a role in the differential extinction rates of European trees, the story is a bit more complicated than that. It turns out that the European mountain ranges don’t present as impenetrable of a barrier to plant migrations as was once thought. The fact that southern Europe and northern Africa share many similar taxa is proof of this. Instead, the amount of suitable habitat and land area available to trees migrating down from northern Europe may have played an even larger role in the extinction rate of European trees.

Extent of glacial coverage (blue) during the last ice age. Map by Hannse Grobe licensed under CC-BY-2.5

It is a well documented phenomenon in ecology that smaller areas of land support smaller numbers of species. This is the case for Pleistocene Europe. Suitable habitat for temperate tree species during this time would have largely consisted of three peninsulas (Iberia, Italy, and the Balkans) separated by the Mediterranian Sea. Each of these peninsulas boast mountain chains that would have offered small bands of suitable microclimates for temperate tree species to find refuge during glacial advance.

Pushed into tiny pockets of refugia, Europe’s temperate tree species would have been more vulnerable to extinction than tree species in North America and Asia, which had far more suitable habitat available to them in the southern portions of those continents. By looking at which taxa survived and which went extinct, patterns do start to emerge. Tree species that are widespread in Europe today are descendants of trees that were far more tolerant of cooler growing seasons and harsh winters than genera that went extinct. This likely reflects the fact that their ancestors were those species that found refuge high up in the mountains.

Alternatively, present-day Europe also boasts small pockets of what are termed “relictual genera,” which is a fancy way of saying species that were once more common in the past than they are today. These so-called relictual taxa have been found to be far more tolerant of drought than genera that went extinct. This likely reflects the fact that their ancestors found refuge in warmer, low-elevation habitats in southern Europe.

It appears that species on either end of the tolerance curves were the ones that won out in Europe’s extinction lottery. By tolerating either extreme cold or extreme drought, “stress tolerators” were able to not only survive repeated glaciation events, but also provide seed sources for those lineages following glacial retreat.

Only the species that were able to find suitable habitats in southern Europe’s glacial refugia were the ones that were able to recolonize the region after the Ice Age had ended. At this point in time, these are some of the best pieces of evidence we have in explaining the disparity in tree diversity between Europe, North America, and Asia. What’s more, I find disturbing trends in such extinctions because it wasn’t like the glaciers always wiped out species immediately. Instead, many species were able to survive glaciation but were pushed into smaller and smaller pockets of suitable habitat until relatively small disturbances pushed them over the edge.

Today, we humans are changing Earth’s climates at a rate that hasn’t been seen in over 50 million years and all the while we are fragmenting habitats more and more. What is going to happen to species living today in these tiny pockets?

Photo Credits: [1] [2]

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

Good News For Mangrove Restoration

Mangrove forests are among the most productive ecosystems on Earth. Bridging the gap between land and sea, these forests function as important habitats for organisms of all shapes, sizes, and ecologies. From a purely structural standpoint, mangrove forests are vital for stabilizing coastlines, reducing erosion, and minimizing damage from storm surges. They are also extremely important habitats for carbon sequestration.

The key component of the carbon storing abilities of mangrove forests involves the formation of peat. Whereas we tend to think of bogs when we think about peat, mangroves form it as well. Peat is the result of the accumulation of partially decomposed vegetation and other organic matter. It’s the partially decomposed part of peat that makes it a major carbon store. Because it doesn’t decompose, all of the carbon locked up in the organic matter stays there instead of entering back into the atmosphere.

As they grow, the roots of mangrove forests accumulate debris and sediments, which builds and builds over time. As the organic layer grows, mangroves grow upward on their propped roots. Over decades and centuries, massive quantities of peat can develop under mangrove forests. This is also one of the ways by which coastal land develops. Needless to say, mangrove forests are extremely important ecosystems.

Photo by Phils 1stPix Licensed under CC BY-NC-SA 2.0

Sadly, because they occur along the coast, mangrove forests the world over have been degraded and destroyed at unsustainable rates. As these forests are razed, the land supporting them erodes, removing all of the accumulated sediments and peat. Not only does this destroy all of the ecological and economic benefits of mangrove forests, it also releases huge quantities of carbon.

In recent years, humans have finally begun to realize the environmental and economic costs of mangrove destruction and many regions are starting to implement mangrove restoration efforts. However, the success of any restoration can sometimes take years or even decades to fully assess. This is where chronosequences come in. By studying mangrove restoration projects at different stages of development, scientists can better understand mangrove restoration efforts over relatively short time periods instead of having to wait for individual projects to age to collect all of their data.

Recently, researchers in Florida decided to look at peat accumulation in various mangrove restoration projects. They looked at mangrove restorations of various ages, spanning 25 years of effort. They found that soil and peat accumulation in these forests is surprisingly rapid. In terms of soil accumulation, restored mangrove forests kept pace with and even outpaced natural mangrove forests within the first 5 years of restoration. Even more exciting, peat accumulation in these restored mangrove forests was very rapid, occurring within only a decade of the completion of a mangrove restoration attempt. When you consider the fact that each of the restoration projects they studied started in nothing but pure sand, these results are extremely encouraging.

The scientists point to mangrove roots as the main driver of soil and peat accumulation in these restored forests. As mangroves grow, their roots expand into the surrounding sand. As roots grow and die, they leave all of that organic matter in the soil. Also, the more roots there are, the more debris like wood, leaves, and sediments get trapped in and around the mangroves. This is why peat accumulation occurs so rapidly. What’s more, as sediment and peat builds up below the mangroves, their height increases. At current, the increase in height of these restored mangrove forests is outpacing the rate of sea level rise in coastal Florida. These are encouraging results when one considers just how fast these coastal habitats are changing as our climate continues to change.

The authors of this research are quick to point out that the fast rates of peat accumulation and mangrove growth are likely to slow as these ecosystems mature. Eventually, many of these processes are likely to balance out. They estimate that it would take at least 55 years for mangrove restoration projects in Florida to match their natural counterparts in terms of ecosystem services. Nonetheless, many components of healthy mangrove ecologies, like herbaceous and juvenile vegetation layers, are already established in restorations long before that 55 year mark.

These results are very exciting. Though there is no substitute for protecting natural mangrove forests (or any wild space for that matter), we need to start putting the pieces of our planet back together. If these data are representative of mangrove restoration efforts across the world, there is hope yet that we can replace at least some of what has been lost. Still, until more of the human race starts to value protecting wild spaces and the species they support, we stand to loose so much more. Support your local land conservancy today!!

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

Further Reading: [1]

Opossum Pollination of a Peculiar Parasite

Floral traits can provide us with insights into the types of pollinators most suited for the job. For many flowering plants, the relationship is relatively easy to understand, but check out the flowers of Scybalium fungiforme. You would be completely excused for not even realizing that these bizarre structures belonged to a plant. The anatomy of those flowers would leave most of asking “what on Earth do they attract?” The answer to this are opossums!

Scybalium fungiforme hails from a peculiar family of parasitic plants called Balanophoraceae and is native to the Atlantic forests of Brazil. Members of this family can be found in tropical regions around the globe and all of them are obligate root holoparasites. Essentially this means that all one ever sees of these plants are their strange flowers. The rest of the plant lives within the vascular system of a host plant’s roots.

The adorable big-eared opossums (Didelphis aurita).

Scybalium fungiforme is particularly strange in that its flowers are covered in scale-like bracts. As such, accessing the flowers would be difficult for most animals. Because its strange blooms superficially resemble some marsupial and rodent pollinated Proteaceae in Australian and South Africa, predictions of a non-flying mammal pollination syndrome were about the only explanations that made sense. Now, with the help of night vision cameras, this prediction has been vindicated.

They key to this unique pollination syndrome lies in those bracts and an interesting aspect of opossum anatomy. Until the scale-like bracts are removed, not much is able to access the floral parts inside. Luckily big-eared opossums (Didelphis aurita) come equipped with opposable toes on their back feet. Upon locating the flowers of S. fungiforme, the opossum uses its back feet to remove the bracts. This unveils a bounty of nectar within. As the opossum feeds, its furry little snout gets covered in pollen. When the opossum visits subsequent flowers throughout the night, pollination is achieved.

Floral visitors of Scybalium fungiforme. b) The big-eared opossum, Didelphis aurita drinking nectar on a plant with five inflorescences (one male and four females). c) The montane grass mouse, Akodon montensis, visiting a plant with about 10 inflorescences and drinking nectar on a female one. d) The Violet-capped Woodnymph hummingbird, Thalurania glaucopis visiting a male and e) a female inflorescence. f) detail of an A. angulata wasp manipulating a male flower to eat pollen. g) Agelaia angulate visiting a female inflorescence with the head inserted among flowers to reach the nectar secreted in the inflorescence receptaculum.

Interestingly, activity doesn’t end when the opossums are done. Enough nectar often remains by the next day that a suite of other animals come to pay a visit to these strange blooms. Day time visitation of S. fungiforme consisted largely of wasps, bees, and even a mouse or two. Researchers were also lucky enough to witness Violet-capped Woodnymph hummingbirds (Thalurania glaucopis) repeatedly visit the flowers for a sip of nectar. It would appear that although the main pollinators of this strange parasite are opossums, the removal of the bracts opens up the flowers for plenty of secondary pollinators as well.

Though this is by no means the only plant to be pollinated by non-flying mammals, this pollination syndrome certainly broadens our understanding of the evolution of pollination syndromes.

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

Further Reading: [1]

Standing up for staghorn sumac

I would like you to truly meet staghorn sumac (Rhus typhina). I say "truly meet" because I know many of you probably have some knowledge of this plant already. If your parents were as misinformed as mine growing up, you were probably raised to believe this plant will cause the same kind of contact dermatitis as poison sumac. Not the case! Though they are related, you probably have not come into contact with poison sumac (Toxicodendron vernix) unless you were hiking around in a bog or other high-quality wetland. Even then, poison sumac is not a common species. The point I am trying to make here is that staghorn sumac is not poisonous!

Staghorn sumac should be celebrated. Few trees can grow in such degraded soil like this tree can. In fact, it is most often encountered in roadside ditches and at the edges of farm fields. In the fall their canopy turns a brilliant shade of red. Seeing a large patch of sumac in full fall color rivals even maples for intensity. Because of this, staghorn sumac can make a beautiful landscape tree. It forms numerous clones from underground roots so that it is rare to see just one tree. Take a step back and look at a staghorn sumac population. They seem to always take on a dome-like shape. Their cloning habit is what gives sumac stand their dome-like appearance. Once a single individual becomes established, it sends out suckers in all directions. The farther out you go from the center of the dome, the younger the clones get.

Since all individuals that sprout from the original tree are clones, entire patches are usually either male or female. Female trees are those that produce the characteristic red, fuzzy seed spikes. The seeds are acrid, oily drupes that are low in fat. Because of this they do not readily spoil and thus stay on the tree in perfect condition all through winter and even into the next season. All of this adds up to sumac seeds being some of the most highly sought after late winter survival foods for birds and mammals. When everything else has been consumed or has spoiled, sumac drupes become very important meals. It is estimated that over 100 bird species will consume sumac fruits. Insects also relish this tree. Countless numbers of them feed on the leaves, flowers, and seeds.

Most importantly in this day and age, the dead stems and branches of this plant make perfect nesting sites for our native solitary bees. They have a soft pith that is easily hollowed out to make egg laying chambers. From carpenter bees to mud wasps, you can find dozens of species nesting in a sumac patch.

Finally, a delicious but tart tea can be made from steeping the seeds in cool water. The longer they steep the stronger the tea. In the heat of summer it is quite refreshing. However, you may want to filter it through a coffee filter before drinking to avoid ingesting the multitudes of larvae that feed in and among them.

Listen to Episode 297 about sumacs and sumac relatives!

Further Reading: [1]

How radioactive carbon from nuclear bomb tests can tell us what parasitic orchids are eating

Yoania japonica. Photo by Qwert1234 licensed by CC BY-NC-SA 4.0

Historically, non-photosynthetic plants were defined as saprotrophs. It was thought that, like fungi, such plants lived directly off of decaying materials. Advances in our understanding have since revealed that parasitic plants don’t do any of the decaying themselves. Instead, those that aren’t direct parasites on the stems and roots of other plants utilize a fungal intermediary. We call these plants mycoheterotrophs (fungus-eaters). Despite recognition of this strangely fascinating relationship, we still have much to learn about what kinds of fungi these plants parasitize and where most of the nutritional demands are coming from.

It is largely assumed that most mycoheterotrophic plants are parasitic on mycorrhizal fungi. This would make them indirect parasites on other photosynthetic plants. The mycorrhizal fungi partner with photosynthetic plants, exchanging soil nutrients for carbon made by the plant during photosynthesis. However, this is largely assumed rather than tested. New research out of Japan has shown a light on what is going on with some of these parasitic relationships and the results are a bit surprising. What’s more, the methods they used to better understand these parasitic relationships are pretty clever to say the least.

Cyrtosia septentrionalis Photo by Qwert1234 licensed by CC BY-NC-SA 4.0

Photosynthesis involves the uptake of and subsequent breakdown of CO2 from the atmosphere. The carbon from CO2 is then used to build carbohydrates, which form the backbone of most plant tissues. Not all carbon is created equal, however, and by looking at ratios of different carbon isotopes in living tissues, scientists can better understand where the carbon came from. For this research, scientists utilized an isotope of carbon called 14C.

Eulophia zollingeri photo by Vinayraja licensed by CC BY-NC-SA 3.0

14C is special because it is not as common in our atmosphere as other isotopes of carbon such as 12C and 13C. One of the biggest sources of 14C in our atmosphere were nuclear bomb explosions. From the 1950’s until the Partial Nuclear Test Ban in 1963, atomic bomb tests were a regular occurrence. During that time period, the concentration of 14C in our atmosphere greatly increased. Any organism that was fixing carbon into its tissues during that span of time will contain elevated levels of 14C compared to the other carbon isotopes. Alternatively, anything fixing carbon today, say via photosynthesis, will have considerably reduced levels of 14C in its tissues.

Gastrodia elata Photo by Qwert1234 licensed by CC BY-NC-SA 4.0

By looking at the ratios of 14C in the tissues of parasitic plants, scientists reasoned that they could assess the age of the carbon being utilized. If more 14C was present, the source of the carbon could not come from today’s atmosphere and therefore not from recent photosynthesis. Instead, it would have to come from older sources like decaying wood of long-dead trees. In other words, if parasitic plants were high in 14C, then the scientists could reasonably conclude that they were parsitizing wood-decaying saprotrophic fungi. If the plants were high in 12C or 13C, then they could conclude that they were partnering with mycorrhizal fungi instead, which were obtaining carbon from present-day photsynthesis.

The researchers looked at 10 different species of parasitic plants across Japan, most of which were orchids. They analyzed their tissues and ran analyses on the carbon molecules within. What they found is that 6 out of the 10 plants contained much higher levels of 12C and 13C in their tissues, which points to mycorrhizal fungi as their host. However, for the 4 remaining species (Gastrodia elata, Cyrtosia septentrionalis, Yoania japonica and Eulophia zollingeri), the ratios of 14C were considerably higher, meaning their host fungi were eating dead wood, not partnering with photosynthetic plants near by.

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Indeed, it appears that at least some mycoheterotrophic plants are benefiting from saprotrophic rather than mycorrhizal fungi. Those early assumptions into the livelihood of such plants were not as far off the mark after all. This is very exciting research that opens the door to a much deeper understanding of some of the strangest plants on our planet.

LEARN MORE ABOUT MYCOHETEROTROPHIC PLANTS IN EPISODE 234 OF THE IN DEFENSE OF PLANTS PODCAST

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

Further Reading: [1] [2]

A Closer Look at Poison Sumac

Photo by JH Miller and KV Miller licensed by CC BY-NC-SA 3.0

Poison sumac (Toxicodendron vernix). The very name is enough to send chills down the spine. At least where I live, this small tree is a bit of a unicorn, often heard of but never seen. That is, unless you know where to look.

A denizen of high quality wetlands, this species is not often encountered by your average hiker. It has a rather spotty distribution in eastern North America as well. I have heard it been said that the best way to find a poison sumac tree is to trip and fall in a bog. The first branch you grab onto will be that of a poison sumac.

Photo by Freekee licensed by CC0 1.0

All jokes aside, coming across one in the wild can be fun. They are a beautiful tree. A member of the family Anacardiaceae, it resembles North America's other sumacs (Rhus sp.), which often gives those innocuous trees a bad reputation. Like its other cousin, poison ivy (Toxicodendron radicans), poison sumac does produce urushiol. Interestingly enough, humans are said to be one of only a small handful of mammals that are susceptible to this compound. The reaction we have to it is not an inherent property of urushiol. Its effects on humans are the result of an allergic reaction. It is said that poison sumac can produce a much harsher reaction than poison ivy. I am one of the lucky ones who does not seem to be allergic to it, which is good news for me as my first encounter with this plant involved most of my face.

Poison sumac fruits are an easy way to tell this tree apart from other sumacs because they produce white-ish fruits, rather than red. Photo by Brett Whaley licensed by CC BY-NC 2.0

Also like poison ivy, poison sumac produces nutritious fruits that birds are particularly fond of. Migratory song birds, especially those that live and breed in wetlands, are the main seed dispersal agents for this species. All in all, the ecological value of species like poison sumac far outweigh the anxieties we feel about them. It is important not to live in fear of species like this. With a little attention to detail, contact can be avoided. Moreover, because it lives in high quality wetlands, the odds of the average person coming into contact with this tree are relatively small compared to other plants. I can only speak highly of a species like this. I just wish we had more high quality wetlands around where they could grow.

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

Further Reading: [1]

Should We Be Calling Aquatic Bladderworts Omnivores Instead of Carnivores?

Photo by Leonhard Lenz licensed under CC BY-NC 2.0

As is so often the case in nature, the closer we start to look at things, the more interesting they become. Take, for instance, the diet of some carnivorous bladderworts (Utricularia spp.). These wonderful organisms cover their photosynthetic tissues in tiny bladder traps that rapidly spring open whenever a hapless invertebrate makes the mistake of coming too close to a trigger hair. The unlucky prey is quickly sucked into the trap and subsequently digested.

This is how most bladderworts supplement their growth. As cool as this mechanism truly is, our obsession with the idea that these plants are strict carnivores has historically biased the kinds of investigations scientists attempt with these plants. Over the last decade or so, closer inspection of the contents of aquatic bladderwort traps has revealed that a surprising amount of plant material gets trapped as well. Most of this material consists of single celled algae. Is it possible that at least some aquatic bladderworts also gain nutrients from all of that “vegetable” matter?

The answer to this question is a bit more nuanced than expected. Yes, it does appear that non-animal material frequently ends up in bladderwort traps. Much of this comes in the form of a wide variety of algae species. What’s more, it does appear that algae are broken down within the traps themselves, suggesting that the bladderworts are actively digesting this material. The main question that needs to be answered here is whether or not the bladderworts actually benefit from the breakdown of algae.

Evidence of a nutritive benefit from algae digestion is mixed. Some studies have found that the bladderworts don’t appear to benefit at all from the breakdown of algae within their traps. Alternatively, others have found that bladderworts may benefit from digesting at least some types of algae. These authors noted that there doesn’t seem to be any benefit in terms of additional nitrogen for the bladderwort but instead suggest that other trace nutrients might be obtained in this way.

One of the biggest hurdles in this line of research arises from the fact that we still don’t fully understand the digestive mechanisms of bladderworts. It is possible that some of the algal degradation within bladderwort traps has nothing to do with digestion at all. Instead, it could simply be that algae stuck in the traps eventually dies and rots away. Another major question raised by these observations is how tiny organisms like single celled algae even make it into the traps in the first place. What we can say for sure is most algae are far too small to actually trigger the bladder traps. As such, algae is either getting into the traps passively via some form of diffusion or they are sucked in when other, larger prey is captured.

Some research has even suggested that the benefit of trapping algae may depend on the habitats in which bladderworts are growing. Bladderworts living in more acidic water have shown to capture far more algae than bladderworts in more neutral or alkaline water. This has to do with acidity. Numerically speaking, there is far less zooplankton living in acidic water than algae, which means algae is more likely to end up in the bladders. It could be that the benefits of algae are thus greater for plants living in places where little zooplankton is available. Certainly more work will be needed before we can call bladderworts omnivores but the idea itself is exciting.

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

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

Rare Plants & Habitat Conservation

In this video, In Defense of Plants explores a chunk of property in southern Appalachia that is slated for housing development. The only reason this land has not yet been converted is because it is very costly to grade on such steep slopes. We will meet some of the many plants that call this slope home, including a very rare sedge, Fraser's sedge (Carex fraseriana). If anything, this video should stand as a reminder that habitat conservation needs to happen at all scales, big and small.

How a cactus from the Andes may be using hairs to attract its bat pollinators

Source: Merlin Tuttle’s Bat Conservation

Plants go to great lengths to attract pollinators. From brightly colored flowers to alluring scents and even some sexual deception, there seems to be no end to what plants will do for sex. Recently, research on the pollination of a species of cactus endemic to the Ecuadorian Andes suggests that even plant hairs can be co-opted for pollinator attraction.

Espostoa frutescens is a wonderful columnar cactus that grows from 1,600 ft (487 m) to 6,600 ft (2011 m) in the Ecuadorean Andes. Like many other high elevation cacti, this species is covered in a dense layer of hairy trichomes. These hairs serve an important function in these mountains by protecting the body of the plant from excessive heat, cold, wind, and UV radiation. Espostoa frutescens takes this a step further when it comes time to flower. It is one of those species that produces a dense layer of hairs around its floral buds called a cephalium. Cacti cephalia are thought to have evolved as a means of protecting developing flowers and fruits from the outside elements. What scientists have now discovered is that, at least for some cacti, the cephalium may also serve an important role in attracting bats.

Bats are famous for their use of echolocation. Because they mainly fly at night, bats rely on sound and scent, rather than sight to find food. More and more we are realizing that a lot of plants have taken advantage of this by producing structures that reflect bat sonar in such a way that makes them more appealing to bats. Some plants, like Mucuna holtonii and Marcgravia evenia, do this for pollination. Others, like Nepenthes hemsleyana, do this to obtain a nitrogen-rich meal.

Espostoa frutescens apparently differs from these examples in that its not about reflecting bat sonar, but rather absorbing it at specific frequencies. Close examination of the hairs that comprise the E. frutescens cephalium revealed that they were extremely well adapted for absorbing ultrasonic frequencies in the 90 kHz range. This may seem arbitrary until you look at who exactly pollinates this cactus.

The main pollinator for E. frutescens is a species of bat known as Geoffroy’s tailless bat (Anoura geoffroyi). It turns out that Geoffroy’s tailless bat happens to echolocate at a frequencies right around that 90 kHz range. Whereas the rest of the body of the cactus reflects plenty of sound, bat calls reaching the cephalium of E. frutescens bounced back an average of 14 decibels quieter.

Essentially, the area of floral reward on this species of cactus presents a much quieter surface than the rest of the plant itself. It is very possible that this functions as a sort of calling card for Geoffroy’s tailless bats looking for their next meal. This makes sense from a communication standpoint in that it not only saves the bats valuable foraging time, it also increases the chances of cross pollination for the cactus. To obtain enough energy from flowers, bats must travel great distances. Anything that helps them locate a meal faster will increase visitation to that flower. By changing the way in which the flowers “appear” to echolocating bats, the cacti thus increase the amount of visitation from bats, which brings pollen in from cacti located over the bats feeding range.

It is important to note that, at this point in time, research has only been able to demonstrate that the hairs surrounding E. frutescens flowers are more absorbent to the ultrasonic frequencies used by Geoffroy’s tailless bat. We still have no idea whether bats are more likely to visit flowers borne from cephalia or not. Still, this research paves the way for even more experiments on how plants like E. frutescens may be “communicating” with pollinators like bats.

Photo by Merlin Tuttle’s Bat Conservation. Please Consider supporting this incredible conservation group!

Further Reading: [1]

Corn Lilies, Cyclops Lambs, and Sonic the Hedgehog

Photo by Judy Gallagher licensed by cc-by-2.0

1957 was an alarming year for Idaho ranchers. Some herds of sheep were giving birth to lambs with severe deformities. The lambs simply weren’t developing right. They emerged from the womb sporting limbs from their heads, incomplete brains, and some of them had only a single, malformed eye in the middle of their face. It would take over a decade before the cause of these deformities was identified and another two decades before we knew why it happened. The first line of evidence came from the weather patterns during that fateful year.

In an average year, sheep usually find enough forage at lower elevations. With plenty of rain keeping plants happy and lush, the sheep don’t have to travel far to find food. Things change during severe droughts. As droughts worsen, plants at lower elevations start to disappear. To find enough food, sheep will move up in elevation where plants are not yet affected by drought. However, the move up slope coincides with a change in the presence and abundance of some plant species. Notably, species like the corn lily (Veratrum californicum) are more prevalent at higher elevations.

Photo by Clint Gardner licensed by CC BY-NC-SA 2.0

Now if there is one common thread that winds its way through the genus Veratrum, it’s the fact that all members produce some seriously potent alkaloid compounds. Though toxicity can vary from species to species, it is a safe bet that most Veratrum can harm you if ingested during their active growing period. However, despite the fact that all parts of Veratrum are toxic, it appears that these Idaho sheep were a bit desperate. It was discovered that during the drought of 1957, some sheep were feeding on the flowers of the V. californicum.

A deformed lamb showing the single, malformed eye and the anomalous limbs.

The flowers themselves aren’t the most toxic part of the plant but they produce measurable levels of toxic alkaloids. After 11 years of studying these malformed sheep, scientists realized that although pregnant sheep could feed on the flowers of V. californicum with no ill effects, they would go on to give birth to the deformed lambs. It became readily apparent that the deformities found in these lambs could be traced back to the consumption of V. californicum.

However, this was not case closed. The ranchers learned that they must keep their sheep away from Veratrum but no one had any idea as to how eating these plants led to such horrible birth defects. It took 25 more years before scientists had that answer.

While studying embryonic development in fruit flies, researchers discovered a set of genes that, when deactivated, cause the flies to grow spiny hairs all over their body. They named this gene “Sonic Hedgehog” after the spiky blue video game character. It turns out that the Sonic Hedgehog gene was extremely important in the development of more organisms than just flies. Importantly, these genes control the way in which the body plan of an organism develops. When something goes wrong with the Sonic Hedgehog pathway, a whole slew of deformities follow. Among these is the development of a single, malformed eye on the middle of the mammalian head.

Luckily, researchers studying Sonic Hedgehog remembered the story of the cyclops sheep in Idaho. It didn’t take long to put the puzzle pieces together. It was soon realized that V. californicum produces one alkaloid in particular that interferes with Sonic Hedgehog. The compound was given the name “Cyclopamine” as a reference to the deformities is caused in those sheep back in 1957. Scientists finally had the smoking gun.

The molecular structure of Cyclopamine

When droughts caused sheep to moved into the mountains in search of plants to munch, some of them would nibble on the flowers of V. californicum. If they were pregnant at the time, enough Cyclopamine made it into their system that it would shut down the Sonic Hedgehog gene pathway in their developing offspring. Once that pathway is shut down, the embryo no longer has a sound blueprint for development and all of those horrendous deformities take place.

The story does not end here. Not only was a 30+ year mystery solved, scientists had come away with a far more detailed understanding embryonic development. They also walked away with some new ideas to test. The most exciting of these involves cancer treatments. It turns out, the Sonic Hedgehog pathway is one of the many pathways involved in a couple different kinds of cancer. Normally, Sonic Hedgehog is dormant in adults but certain circumstances can see it reactivate and go into overdrive, leading to cancerous tumors. Some scientists are now using Cyclopamine to turn off the Sonic Hedgehog pathway in those tumors as a form of cancer treatment.

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

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

Buckthorns Gone Wild

Colletia paradoxa photo by James Gaither licensed by CC BY-NC-ND 2.0

When I think of the buckthorn family (Rhamnaceae), my mind conjures up images of battling with Rhamnus invasions around the Great Lakes or the amazing diversity of Ceanothus in western North America. Never have my thoughts drifted to the bizarre and wonderful genus Colletia. Native to temperate regions of South America, this strange group of spiny shrubs is certainly worth a closer look.

Though new to me, the genus Colletia has been known to science and horticulture since at least the late 1700’s. Hailing from temperate climates, at least two of the five known species of Colletia have found there way into temperate gardens elsewhere. Who could blame gardeners for their fascination with these shrubs. Close inspection of Colletia reveals surprisingly complex morphological features.

Colletia paradoxa

For starters, those large, thick, leaf-like thorns are not leaves at all. They are flattened extensions of the stem called cladodes. Instead of relying on leaves for most of their photosynthetic needs, the various Colletia instead produce chlorophyll in their stems. The cladodes function in much the same way as leaves in that their increased surface area maximizes photosynthetic potential. It is likely that cladodes are a means of conserving valuable resources for the plant.

Instead of producing vulnerable leaves that are subject to plenty of damage, these shrubs simply utilize stem tissues. Stems don’t need to be regrown year after year and by adorning the tips of the cladodes with spines, the plant is better able to protect its photosynthetic tissues. That is not to say that Colletia produce no leaves at all. Colletia will produce leaves near the base of each cladode, especially on younger tissues. Leaves, however, are deciduous and don’t stick around long enough to do much photosynthesizing.

Colletia ulicina with its red, tubular flowers. Photo by FarOutFlora licensed by CC BY-NC-ND 2.0

The flowers of Colletia ulicina are pollinated by hummingbirds. photo by James Gaither licensed by CC BY-NC-ND 2.0

Colletia are made all the more noticeable when they come into flower. For most species, clusters of lightly-scented, white flowers are produced at the base of the cladodes. For these species, insects are thought to be the predominant pollinators. Such is not the case for Colletia ulicina. This species produces sprays of bright red, tubular flowers along its stems. In the wild, these are pollinated by the green-backed firecrown hummingbird (Sephanoides sephaniodes).

Another interesting aspect of Colletia ecology is that they are all nitrogen fixers. To be fair, the plants themselves don’t do any of the fixing. Instead, they produce tiny structures on their roots called “nodules,” and those nodules house specialized bacteria collectively referred to as actinomycetes. In exchange for carbohydrates produced via photosynthesis, these bacteria fix nitrogen from the air. This extra boost of nitrogen allows Colletia to survive and excel in the nutrient-poor soils they call home.

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

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

Salty Succulents

Photo by Leoboudv licensed by CC BY 2.5

Succulent plants come in a variety of shapes, sizes, and colors. They also hail from a variety of plant families. If there is one thing that unites these plants (other than their succulent habit) its that the vast majority of them around found growing in dry places. Whether its the heart of a desert or up in the canopy of a tree, succulence has evolved as a means of storing water. However, those of you living near salt marshes may recognize that a handful of salt marsh plants are succulent as well. How is it that plants so frequently found growing in standing water have evolved a succulent habit? The answer lies in salt.

Salt water is pretty bad for most plants. Just like we get dehydrated from drinking or eating high amount of salt, so too do plants. In general, salt both dehydrates plants and causes issues with nutrient uptake. Such is not the case for genera like Salicornia. Commonly referred to as glassworts, pickleweeds, or picklegrass, the various Salicornia are true salt-lovers.

Photo by OliBac licensed by CC BY 2.0

Taxonomically speaking, the genus Salicornia has been called a “taxonomic nightmare.” Thanks to their highly reduced morphology and extreme phenotypic plasticity, delineating species among the genus is something best left to Salicornia experts. What we do know is that they all belong in the amaranth family, Amaranthaceae. All of this confusion should not take away from your enjoyment of Salicornia. Indeed, there is a lot worth appreciating in this family, including their ability to grow in conditions that would kill most other plants.

Salicornia are not simply salt tolerators that can hang on under saline conditions. They are true salt lovers or ‘halophytes.’ In fact, experiments have shown that various Salicornia grow much better when salt levels are high. This all has to do with the way in which these plants deal with their salty environment. Like all succulents, Salicornia have enlarged vacuoles that store water. However, these large vacuoles store more than good ol H2O. They also store salts and lots of them.

Photo by S.Ahmadihayeri licensed by CC BY-SA 3.0

The secret to Salicornia’s salty success has to do with osmosis. As you may remember from science class, substances in our universe like to move from areas of high concentration to areas of low concentration. In the case of water within the tissues of an organism, this often occurs between biological membranes. As you add salt to water, it actually displaces water molecules such that the more salt you add, the less concentrated the water becomes. That is why salt water dehydrates us. When you surround a cell with salt, water will diffuse out of the cell to balance out the concentrations on both sides of the cell membrane. Salicornia use this to their advantage.

These plants actively take up salt from their environment and dump it into their vacuoles. This means that the concentration of water within the vacuole is less than the concentration of water outside of the cell. Osmosis then takes over and water rushes into the plant’s cells. By concentrating salt in their vacuoles, Salicornia are always ensuring that they are on the receiving end of the water gradient. Water is always moving into these salty plants and not the other way around. By co-opting morphological adaptation to drought, Salicornia are able to conquer a niche that is largely unavailable to most other plant species. It also means that, despite all of the water in their environment, these plants maintain a pleasingly succulent habit.

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

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

The Sinewy American Hornbeam

Photo by Richard Webb licensed by CC BY-SA 3.0

Winter is when I really start to notice trees. Admittedly, I am pretty poor when it comes to tree ID and taxonomy but there are a few species that really stand out. One of my all time favorite trees is Carpinus caroliniana.

Carpinus caroliniana goes by a handful of common names including ironwood, musclewood, and American hornbeam. All of these names have been applied to other trees so I'll stick with its scientific name. Finding C. caroliniana is rather easy. All you have to do is look for its unmistakable bark.

Photo by Rob Duval licensed by CC BY-SA 3.0

With smooth, sinewy striations and ridges, it is no wonder how this tree got the name "musclewood." The wood is extremely close-grained and is therefore very hard, earning it another nickname of "ironwood."They are generally small trees, rarely exceeding a few meters in height, though records have shown that some individuals can grow to upwards of 20 meters in rare circumstances. I hope that someday I will be able to meet one of these rare giants.

Carpinus caroliniana is also an indicator of fairly rich soils. Due to their high tolerance for shade, they are often a tree of the mixed hardwood understory. Their foliage resembles that of the family in which they belong, the birch family (Betulaceae).

Photo by Katja Schulz licensed by CC BY 2.0

The caterpillar of the io moth (Automeris io)

An adult io moth (Automeris io). Photo by Andy Reago & Chrissy McClarren licensed by CC BY 2.0

A multitude of insect species utilize C. caroliniana as a larval food source including the famed io moth. In the spring, male and female catkins are born on the same tree and, after fertilization, they are replaced by interesting looking nutlets covered by leaf-like involucres. The seeds are an important food source for a variety of birds, mammals, and insects alike.

The male flowers of Carpinus caroliniana. Photo by Philip Bouchard licensed by CC BY-NC-ND 2.0

Carpinus caroliniana is a tree I could never get bored with. Not only does it have immense ecological value, it is aesthetically pleasing too. Its small size and shade tolerance also makes it a great landscape tree in areas too cramped for something larger. Why this species isn't more popular in native landscaping is beyond me.

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

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

To grow or to flower, that is the cactus conundrum

Melocactus intortus

Flowers are costly structures for plants to produce. In the flowering plant world, there is always a trade-off between growth and reproduction. Flowers are produced from tiny structures called axillary buds, and many plants can only produce one flush of flowers per bud. Cacti are no exception to this rule and their amazing morphological adaptations to harsh climates has forced them into quite a conundrum when it comes to reproduction.

The axillary buds of cacti are located at the base of their spines in little structures called areoles. This is where the flowers will eventually emerge. However, unlike plants that can produce cheap stems and branches, cacti must produce a whole new chunk of stem or internode before they can produce more axillary buds. Think of it this way, if a cactus wants to produce 10 flowers, it must produce ten internodes to do so. This means producing all of the expensive cortex and epidermis along with it. Their harsh environments have forced most cacti into an extremely tight relationship between growth, water storage, photosynthesis, and flowering that is potentially very limiting from a reproductive standpoint.

Micranthocereus estevesii with lateral cephalium

Amazingly, some cacti have managed to break from this evolutionary relationship and they have done so in a bizarre way. Take a look at all of the cacti pictured here. Each has developed a strange looking structure called a cephalium. Essentially, you can think of the cephalium of a cactus as its “adult” reproductive form whereas the rest of the body consists of non-reproductive, photosynthetic “juvenile” form.

The cephalium is a unique and fascinating structure. It differs from the rest of the cactus body in that it is not photosynthetic. It also produces no chlorophyll and no stomata. In fact, it does not form anything like the epidermis of the rest of the plant. Instead, the cephalium produces dense clusters of short spines and trichomes. Most importantly, it produces tightly packed axillary buds in high abundance. These are the buds that will produce the flowers. The end result is a wacky looking structure that has the ability to produce far more flowers than that of cacti that do not grow a cephalium.

Facheiroa tenebrosa with lateral cephalium

Obviously not all cacti produce cephalia but it is common in genera such as Melocactus, Backebergia, Espostoa, Discocactus, and Facheiroa (this is not a complete list). What the cephalium has done for genera like these is decouple the afore mentioned relationships between growth and reproduction. For a period of time (often many years) following germination, these cacti grow the typical succulent, photosynthetic stems we are accustomed to seeing.

At some point in their development, something triggers these plants to switch to their adult forms. Axillary buds within either lateral or apical meristems switch their growth habit and begin forming the cephalium. It is worth mentioning that no one yet knows what triggers this switch. If the cephalium is produced from axillary buds in the apical meristem like we see in Melocactus, the plant will no longer produce photosynthetic tissues. This represents another major trade-off for these cacti. Such species must rely on the photosynthetic juvenile tissues for all of their photosynthetic needs for the rest of their lives (unless the cephalium is damaged or lost). Backebergia have managed to get around this trade-off by not only growing multiple stems, they will also shed their apical cephalia after a few years, thus re-initiating photosynthetic juvenile growth.

Backebergia militaris with bizarre apical cephalia reminiscent of the bearskin hats of the Queen’s guard.

Things are a bit different for cacti that produce lateral cephalia. Genera such as Espostoa, Facheiroa, and Buiningia are less limited by their cephalia because they are produced along the ribs of the stem, thus leaving the apical meristem free to continue more typical photosynthetic growth. Nonetheless, the process is much the same. Dense clusters of spines, trichomes, and most importantly, axillary buds are produced along the rib, giving each stem a lovely, lopsided appearance.

There are other benefits to growing cephalia in addition to simply being able to produce more flowers. The densely packed spines and trichomes offer the developing flowers and fruits ample protection from both the elements and herbivores. Floral buds are free to develop deep within the interior of the cephalium until they are mature. At that point, the cells will begin to swell with water, pushing the flower outward from the cephalium where it will be exposed to pollinators. As the petals curl back, they offer a safe spot for visiting pollinators that is free from menacing spines. Once pollination has been achieved, the flower wilts and the deeply inferior ovaries are then free to develop within the safety of the cephalium. Once the fruits are mature, they too will begin to swell with water and be pushed out from the cephalium where they will attract potential seed dispersers.

Melocactus violaceus with fruits emerging from the cephalium

I hope that I have convinced you of just how awesome this growth form can be. I will never forget the first time I saw a cactus topped with a cephalium. It was a mature Melocactus growing in a cactus house. Sticking out of the odd “cap” on top was a ring of bright pink fruits. I knew nothing of the structure at that time but it was incredible to see. Now that I know what it is and how it functions, I am all the more appreciative of these cacti.

This post was inspired by the diligent work of Dr. Jim Mauseth. Click here to learn more about cacti.

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

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

What an orchid that smells like rotting meat can tell us about carrion flies

Satyrium pumilum Photo by Bernd Haynold licensed by CC BY-SA 3.0

Orchids are really good at tricking pollinators. Take, for instance, this strange looking orchid from South Africa. Satyrium pumilum is probably obscure to most of us but it is doing fascinating things to ensure its own reproductive success. This orchid both smells and kind of looks like rotting meat, which is how it attracts its pollinators.

It is a bit strange to think of orchids living in arid climates like those found in South Africa but this family is defined by exceptions. That is not to say that Satyrium pumilum is a desert plant. To find this orchid, you must look in special microclimates where water sticks around long enough to support its growth. Populations of S. pumilum are most often found clustered near small streams or hidden under bushes throughout the western half of the greater Cape Floristic Region.

Satyrium pumilum blooms from the beginning of September until late October. As is typical in the orchid family, S. pumilum produces rather intricate flowers. Whereas the sepals are decked out in various shades of green, the interior of the flower is blood red in color. Also, unlike many of its cousins, S. pumilum doesn’t throw its flowers up on a tall stalk for all the world to see. Instead, its flowers open up at ground level and give off an unpleasant smell of rotting meat.

This is where pollinators enter into the picture. It has been found that carrion flies are the preferred pollinator for S. pumilum. By producing flowers at ground level that both look and smell like rotting meat, the plants are primed to attract these flies. The plants are tapping into the flies’ reproductive habits, a biological imperative so strong that they simply do not evolve a means of discriminating a rotting corpse from a flower that smells like one. This is the trick. Flies land on the flower thinking they have found a meal and a place to lay their eggs. They go through the motions as expected and pick up or deposit pollen in the process. Unfortunately for the flies, their offspring are doomed. There is not food to be found in these flowers.

What is most remarkable about the reproductive ecology of S. pumilum is that not just any type of fly will do. It appears that only a specific subset of flies actually visit the flowers and act as effective pollinators. Amazingly, this provides insights into some long-running hypotheses regarding carrion fly ecology.

(A) The habitat of S. pumilum (B) Satyrium pumilum in situ (scale bar = 1 cm). (C–E) Pollination sequence of a S. pumilum flower by a sarcophagid fly in an arena (scale bar for all three photos = 0·5 cm); (C) the fly carrying five pollinaria from other S. pumilum flowers enters an unpollinated flower (D) as the fly moves deeper into the flower towards the right-hand spur, it presses an attached pollinium against the stigma, and its thorax against the right-hand viscidium; (E) as it leaves the flower, the fly has deposited two massulae on the stigma (1), and removed a pollinarium (2) – it now carries six pollinaria. [SOURCE]

Apparently there has been a lot of debate in the fly community over why we see so many different species of carrion flies. Rotting meat is rotting meat, right? Probably not, actually. Fly ecologists have comes up with a few hypotheses involving niche segregation among carrion flies to explain their diversity on the landscape. Some believe that flies separate themselves out in time, with different species hatching out and breeding at different times of the year. Others have suggested that carrion flies separate themselves by specializing on carrion at different stages of decay. Still others have suggested that some flies specialize on large pieces of carrion whereas others prefer smaller pieces.

By studying the types of flies visiting the flowers of S. pumilum researchers did find evidence of niche segregation based on carrion size. It turns out that S. pumilum is exclusively pollinated by a group of flies known as sarcophagid carrion flies. These flies were regularly observed with orchid pollen sacs stuck to their backs and plants seemed to only set seed after they had been visited by members of this group. So, what is it about these flowers that makes them so specific to this group of flies?

The answer lies both in their size as well as the amount of scent they produce. It is likely that the quantity of scent compounds produced by S. pumilum most closely mimics that of smaller rotting corpses. The types of flies that visited these blooms were mostly females of species that lay relatively few eggs compared to other carrion flies. It could very well be that the smaller brood size of these flies allows them to effectively utilize smaller bits of carrion than other, more fecund species of fly. To date, this is some of the best evidence in support of the idea that flies avoid competition among different species by segregating out their feeding and reproductive niches.

Rotting meat smells are not uncommon in the plant world. Even within the home range of S. pumilum, there are other plants produce flowers that smell like carrion as well. It would be extremely interesting to look at what kinds of flies visit other carrion flowers and in what numbers. Like I mentioned earlier, reproductive is such a major part of any organisms life that it may simply be too costly for carrion flies to evolve a means of discriminating real and fake breeding sites. It is amazing to think of what we gain from trying to understand the reproductive biology of a small, obscure orchid growing tucked away in arid regions of South Africa.

Photo Credits: [1] [2]

Further Reading: [1]