Category: Plants

Fir Trees & Building the World of the Distant Past

Understanding when and where a group of species evolved tells a story of the world they emerged into.

This past week, I had an interesting new scientific paper come across my desk, on the systematics of fir trees – genus Abies in the Pine family. I realize fir tree systematics is not what the average person might consider compelling reading, but if you look past the statistical tests and lines of code, systematics can be great reading for the imagination. In this paper, the researchers reconstructed the speciation pulse (a period of time when a bunch of species came into existence fairly quickly) of fir trees native to the Mediterranean Basin, then dated it using fossils. The main finding of the paper was that this burst had actually happened millions of years earlier than had been supposed.

The really neat part is how they then used this finding to paint a picture of the world when fir trees were colonizing the Mediterranean. At the time these fir trees diversified, what we now think of as the Mediterranean climate, temperate and favourable to biodiversity, didn’t exist, and wouldn’t for tens of millions of years yet. At this time, the Oligocene-Miocene boundary, around 23 million years ago, the global climate had been cooling for some time, which favoured the expansion of gymnosperms like firs. A single ancestor came to the Mediterranean from Asia and quickly (for trees) spread through the whole of the Mediterranean Basin, leaving a dozen or so new species in its wake. This was going on at a time when the first apes were evolving and glasslands were just forming for the first time. The Andes didn’t exist yet and Australia was moving northward and drying out. What we now know about Mediterranean fir trees adds a new detail to this picture of a world very different from, but turning into, our own.

In my own work on the systematics of the Dialiinae, I’ve always been captivated by a genus called Labichea. It’s a group of about 14 shrubs native to Queensland, Australia. The earlier evolving species of the genus have pinnate leaves with broad leaflets, sort of like walnut trees (but smaller and more oval). From this, there is an evolutionary progression to species with fewer leaflets, becoming long and thin, covered with hairs to keep the wind from pulling water away form the surface. They become tougher and more leathery to the touch. In one species, the leaflets have narrowed and curled up on themselves so much that they are, for all intents and purposes, needles now. Lining these species up next to one another is like watching a plant evolve and adapt to an increasingly hot, dry Australian outback in real time.

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Labichea stellata, one of the intermediate forms, with tough, leathery, narrow leaves adapted to a hot, dry climate.

Studying the morphology – the physical form – of a plant will tell you a lot about the challenges of the place it evolved and what it had to survive to make it to today, but reconstructing the evolutionary tree of a group creates a sort of speculative saga of a group of species changing as the world changed and it pushed out to new territories and new niches. 

I think that’s the difference between finding science a collection of dry facts and finding it utterly compelling to learn about… knowing that you need to see the forest rather than just the trees, and to find the story of life that all those facts come together to tell you.

 

[Note to sharp readers: yes, I know those are not fir trees in the image. But those are definitely the mists of time you’re seeing between them.]

Storage & Survival in the Palm Family

Palm trees have had to develop some creative strategies to survive drought and cool climates.

My recent work with Botany One writing news briefs for newly published botany research has had me reading a lot of scientific articles, and it just so happens that twice in the last couple of weeks, they’ve dealt with new research on palms. Having worked mostly on legumes as a researcher, I’d never given much thought to these fascinating plants, beyond the fact that they look good on a tropical beach. But there’s a lot to them, as I’ve been finding out lately, and I thought I’d write a little post to share what I’ve learned.

Palms are members of the Arecaceae family, which has around 2600 species spread through the world’s tropical and subtropical regions. They are monocots, like grasses or orchids. The arborescent, or tree-like, members of the palm family – what we’d call a palm tree – are unique among tall trees in that they have no vascular cambium. This is the cell layer in the trunk of a tree that allows it to widen year upon year, and is also responsible for tree growth rings. If you cut a palm tree down, there are no annual rings in its trunk, because that trunk didn’t continue to grow. (It’s also why their trunks look so cylindrical, as opposed to the usual tapering you see in a tree trunk.) This imposes some interesting restrictions on the tree. For instance, the tree’s vasculature cannot be renewed, as it is in other trees. The cells making up the tubes that transport water and nutrients through the trunk must last the entire life of the tree, which can be upwards of 100 years in some species.

While more than 90% of palms are restricted to tropical rainforests, some also occur in cool, high altitude regions and arid deserts. Unlike most of the plants that live in cool and dry habitats, palms lack dormancy mechanisms, such as dropping their leaves, that would help them to survive these conditions. What’s more, like all monocots, palms have no central tap root that will allow them to reach deeper reserves of soil water. So they’ve had to develop some creative survival strategies. Under drought conditions, which some palm trees endure regularly due to their arid habitat, the greatest danger to a plant is vascular embolism. This happens when the water column that runs through the plant breaks because there’s not enough water, and air bubbles form and expand through the xylem tubes. Once a certain amount of air is present in the tube, it will never function again and the tissue it feeds will die. To help counter this, palm trees store water in parenchyma cells adjacent to the xylem, so that when an embolism is imminent, more water can be shifted into the column. Their anatomy also encourages embolisms that do happen to happen closer to the tip of the leaf, as opposed to near or inside the trunk, where they would do greater damage. 

Palms have a neat survival trick to help their seeds germinate in the low temperatures. Most palms store oil in their seeds to provide sustenance for the seedling when it germinates. This is usually high in saturated fats, which aren’t liquid at low temperatures. This would mean that seeds either couldn’t germinate under cool conditions, or would risk starvation if they did. New research has found that palms growing in cooler climates have evolved their own oil blend rich in unsaturated fats, which are liquid at lower temperatures, to help their seeds thrive in those habitats.

Speaking of oil storage, palms have been hugely important to human beings since before the dawn of civilization, all thanks to those oils, which can occur in both the seed and the fruit, and provide a high calorie food source. The best known is coconut, Cocos nucifera, with its greasy, delicious seed, which we eat as a fruit. In fact, the fruit of a coconut isn’t a nut at all, it’s a drupe. But while coconut is perhaps the most familiar palm food, the most economically important is certainly the oil palm, genus Elaeis. The oil that comes from this palm is high in saturated fat, making it useful for deep-frying (and bio-fuel), if not the best for your health. The use of palm oil is controversial, because of the environmental and human rights abuses linked to its production, yet production is ongoing in regions of Africa, Asia, and the Americas. Outside of their oil production, palms are also the source of dates, palm syrup, carnauba wax, and wood.

Recent research has found that the seeds with the greatest oil storage are all grouped in the tribe Cocoseae, but that palms with oily fruits and moderately oily seeds abound throughout the family, suggesting there may yet be nutritionally and economically valuable species that haven’t been discovered, though whether the further exploitation of these resources is a welcome development is debatable. 

What’s in a Name?

Part Two: How’s Your Latin?

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The awesomely named Obamadon gracilis.  Image: Reuters

What do Barack Obama, Marco Polo, and the band Green Day have in common? They all have at least one organism named after them. Obama has several, including a bird called Nystalus obamai and an extinct reptile named Obamadon gracilis. Green Day’s honorary organism is the plant Macrocarpaea dies-viridis, “dies-viridis” being Latin for “green day.” Many scientists also have species named after them, usually as recognition for their contributions to a field. My own PhD advisor, Dr. Anne Bruneau, has a genus of legumes, Annea, named after her for her work in legume systematics.

Nashi_pear
“Pear-leaved Pear”   Photo via Wikimedia Commons

Scientific names, which are colloquially called Latin names, but which often draw from Greek as well, consist of two parts: the genus, and the specific epithet. The two parts together are called the species. Though many well-known scientists, celebrities, and other note-worthies do have species named after them, most specific epithets are descriptive of some element of the organism or its life cycle. Many of these are useful descriptions, such as the (not so bald) bald eagle, whose scientific name is the more accurate Haliaeetus leucocephalus, which translates to “white-headed sea eagle.” (See here for some more interesting examples.) A few are just botanists being hilariously lazy with names, as in the case of Pyrus pyrifolia, the Asian pear, whose name translates as “pear-leaved pear.” So we know that this pear tree has leaves like those of pear trees. Great.

In contrast to common names, discussed in our last post, Latin names are much less changeable over time, and do not have local variants. Soybeans are known to scientists as Glycine max all over the world, and this provides a common understanding for researchers who do not speak the same language. Latin is a good base language for scientific description because it’s a dead language, and so its usage and meanings don’t shift over time the way living languages do. Until recently, all new plant species had to be officially described in Latin in order to be recognized. Increasingly now, though, descriptions in only English are being accepted. Whether this is a good idea remains to be seen, since English usage may shift enough over the years to make today’s descriptions inaccurate in a few centuries’ time.

This isn’t to say that scientific names don’t change at all. Because scientific names are based in organisms’ evolutionary relationships to one another (with very closely related species sharing a genus, for example), if our understanding of those relationships changes, the name must change, too. Sometimes, this causes controversy. The most contentious such case in the botanical world has been the recent splitting of the genus Acacia.

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The tree formerly known as Acacia. Via: Swahili Modern

Acacia is/was a large genus of legumes found primarily in Africa and Australia (discussed previously on this blog for their cool symbiosis with ants). In Africa, where the genus was first created and described, the tree is iconic. The image of the short, flat-topped tree against a savanna sunset, perhaps accompanied by the silhouette of a giraffe or elephant, is a visual shorthand for southern Africa in the popular imagination, and has been used in many tourism campaigns. The vast majority of species in the genus, however, are found in Australia, where they are known as wattles. When it became apparent that these sub-groups needed to be split into two different genera, one or the other was going to have to give up the name. A motion was put forth at the International Botanical Congress (IBC) in Vienna in 2005 to have the Australian species retain the name Acacia, because fewer total species would have to be renamed that way. Many African botanists and those with a stake in the acacias of Africa objected. After all, African acacias were the original acacias. The motion was passed, however, then challenged and upheld again at the next IBC in Melbourne in 2011. (As a PhD student in legume biology at the time, I recall people having firm and passionate opinions on this subject, which was a regular topic of debate at conferences.) It is possible it will come up again at this year’s IBC in China. Failing a major turnaround, though, the 80 or so African acacias are now known as Vachellia, while the over one thousand species of Australian acacias continue to be known as Acacia.

The point of this story is, though Latin names may seem unchanging and of little importance other than a means of cataloguing species, they are sometimes both a topic of lively debate and an adaptable reflection of our scientific understanding of the world.

Do you have a favourite weird or interesting Latin species name? Make a comment and let me know!

What’s in a Name?

Part One: Common vs. Scientific Names

img_3146-staghornsumac

When I was a kid growing up on a farm in southwestern Ontario, sumac seemed to be everywhere, with its long, spindly stems, big, spreading compound leaves, and fuzzy red berries. I always found the plant beautiful, and had heard that First Nations people used the berries in a refreshing drink that tastes like lemonade (which is true… here’s a simple recipe). But often, we kids were warned by adults that this was “poison sumac,” not to be touched because it would give us itchy, burning rashes, like poison ivy did. In fact, plenty of people would cut down any nascent stands to prevent this menace from spreading. We were taught to fear the stuff.

 

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THIS is the stuff you need to look out for. Via The Digital Atlas of the Virginia Flora

It was many years later before I learned that the red-berried sumacs I grew up with were not only harmless, but were also not closely related to the poisonous plant being referred to, which, as it turns out, has white berries and quite different leaves. Scientifically speaking, our innocent shrub is Rhus typhina, the staghorn sumac, while the rash-inducing plant is called Toxicodendron vernix. Not even in the same genus. Cautious parents were simply being confused by the similarity of the common names.

 

This story illustrates one of the ironies of common names for plants (and animals). Though they’re the way nearly everyone thinks of and discusses species, they’re without a doubt the most likely to confuse. Unlike scientific (Latin) names, which each describe a single species and are, for the most part, unchanging, a single common name can describe more than one species, can fall in and out of use over time, and may only be used locally. Also important to note is that Latin names are based on the taxonomy, or relatedness, of the species, while common names are usually based on either appearance, usage, or history.

 

This isn’t to say that common names aren’t valuable. Because common names describe what a plant looks like or how it is used, they can convey pertinent information. The common names of plants are also sometimes an important link to the culture that originally discovered and used the species, as in North America, where native plants all have names in the local languages of First Nations people. It seems to me, although I have no hard evidence to back it up, that these original names are now more often being used to form the Latin name of newly described species, giving a nod to the people who named it first, or from whose territory it came.

 

One high profile case of this in the animal world is Tiktaalik roseae, an extinct creature which is thought to be a transitional form (“missing link”) between fish and tetrapods. The fossil was discovered on Ellesmere Island in the Canadian territory of Nunavut, and the local Inuktitut word “tiktaalik”, which refers to a type of fish, was chosen to honour its origin.

 

But back to plants… Unlike staghorn sumac and poison sumac, which are at least in the same family of plants (albeit not closely related within that family), sometimes very distinct species of plants can end up with the same common name through various quirks of history. Take black pepper and bell or chili peppers. Black pepper comes from the genus Piper, and is native to India, while hot and sweet peppers are part of the genus Capsicum. Botanically, the two are quite distantly related. So why do they have the same name? Black pepper, which bore the name first, has been in use since ancient times and was once very highly valued. The confusion came about, it would seem, when Columbus visited the New World and, finding a fruit which could be dried, crushed, and added to food to give it a sharp spiciness, referred to it as “pepper” as well.

Sa-pepper
A black peppercorn. Easy to confuse with a chili pepper, I guess? Via: Wikimedia Commons

 

Another interesting, historically-based case is that of corn and maize. In English-speaking North America, corn refers to a single plant, Zea mays. In Britain and some other parts of the Commonwealth, however, “corn” is used to indicate whatever grain is primarily eaten in a given locale. Thus, Zea mays was referred to as “Indian corn” because it was consumed by native North Americans. Over time, this got shortened to just “corn”, and became synonymous with only one species. Outside of Canada and the United States, the plant is referred to as maize, which is based on the original indigenous word for the plant. In fact, in scientific circles, the plant tends to be called maize even here in North America, to be more exact and avoid confusion.

 

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Not Spanish, not a moss. Via: Wikimedia Commons

And finally, for complete misinformation caused by a common name, you can’t beat Spanish moss. That wonderful gothic stuff you see draped over trees in the American South? That is neither Spanish, nor a moss. It is Tillandsia usneoides, a member of the Bromeliaceae, or pineapple family, and is native only to the New World.

 

And that wraps up my very brief roundup of confusing common names and why they should be approached with caution. In part two, I’ll discuss Latin names, how they work, and why they aren’t always stable and unchanging, either.

 

There are SO many more interesting and baffling common names out there. If you know of a good one, let me know in the comments!

 

*Header image via the University of Guelph Arboretum

Sex & the Reign of the Red Queen

Why sexual species beat clones every time.

Tenniel_red_queen_with_alice

“Now, here, you see, it takes all the running you can do to keep in the same place.”

From a simple reproductive perspective, males are not a good investment. With apologies to my Y chromosome-bearing readers, let me explain. Consider for a moment a population of clones. Let’s go with lizards, since this actually occurs in lizards. So we have our population of lizard clones. They are all female, and are all able to reproduce, leading to twice the potential for creating more individuals as we see in a species that reproduces sexually, in which only 50% of the members can bear young. Males require all the same resources to survive to maturity, but cannot directly produce young. From this viewpoint alone, the population of clones should out-compete a bunch of sexually-reproducing lizards every time. Greater growth potential. What’s more, the clonal lizards can better exploit a well-adapted set of genes (a “genotype”); if one of them is well-suited to survive in its environment, they all are.

Now consider a parasite that preys upon our hypothetical lizards. The parasites themselves have different genotypes, and a given parasite genotype can attack certain host (i.e. lizard) genotypes, like keys that fit certain locks. Over time, they will evolve to be able to attack the most common host genotype, because that results in their best chance of survival. If there’s an abundance of host type A, but not much B or C, then more A-type parasites will succeed in reproducing, and over time, there will be more A-type parasites overall. This is called a selection pressure, in favour of A-type parasites. In a population of clones, however, there is only one genotype, and once the parasites have evolved to specialise in attacking it, the clones have met their match. They are all equally vulnerable.

The sexual species, however, presents a moving target. This is where males become absolutely worth the resources it takes to create and maintain their existence (See? No hard feelings). Each time a sexual species mates, its genes are shuffled and recombined in novel ways. There are both common and rare genotypes in a sexual population. The parasite population will evolve to be able to attack the most common genotype, as they do with the clones, but in this case, it will be a far smaller portion of the total host population. And as soon as that particular genotype starts to die off and become less common, a new genotype, once rare (and now highly successful due to its current resistance to parasites), will fill the vacuum and become the new ‘most common’ genotype. And so on, over generations and generations.

Both species, parasite and host, must constantly evolve simply to maintain the status quo. This is where the Red Queen hypothesis gets its name: in Wonderland, the Red Queen tells Alice, “here, you see, it takes all the running you can do to keep in the same place.” For many years, evolution was thought of as a journey with an endpoint: species would evolve until they were optimally adapted to their environment, and then stay that way until the environment changed in some fashion. If this was the case, however, we would expect that a given species would be less likely to go extinct the longer it had existed, because it would be better and better adapted over time. And yet, the evidence didn’t seem to bear this prediction out. The probability of extinction seemed to stay the same regardless of the species’ age. We now know that this is because the primary driver of evolution isn’t the environment, but competition between species. And that’s a game you can lose at any time.

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Passionflower. Photo by Yone Moreno on Wikimedia Commons.

Now the parasite attacking the lizards was just a (very plausible) hypothetical scenario, but there are many interesting cases of the Red Queen at work in nature. And it’s not all subtly shifting genotypes, either; sometimes it’s a full on arms race. Behold the passionflower. In the time of the dinosaurs, passionflowers developed a mutually beneficial pollinator relationship with longwing butterflies. The flowers got pollinated, the butterflies got nectar. But then, over time, the butterflies began to lay their eggs on the vines’ leaves. Once the eggs hatched, the young would devour the leaves, leaving the plant much the worse for wear. In response, the passionflowers evolved to produce cyanide in their leaves, poisoning the butterfly larvae. The butterflies then turned the situation to their advantage by evolving the ability to not only eat the poisonous leaves, but to sequester the cyanide in their bodies and use it to themselves become poisonous to their predators, such as birds. The plants’ next strategy was to mimic the butterflies’ eggs. Longwing butterflies will not lay their eggs on a leaf which is already holding eggs, so the passionflowers evolved nectar glands of the same size and shape as a butterfly egg. After aeons of this back and forth, the butterflies are currently laying their eggs on the tendrils of the passionflower vines rather than the leaves, and we might expect that passionflowers will next develop tendrils which appear to have butterfly eggs on them. These sorts of endless, millennia-spanning arms races are common in nature. Check out my article on cuckoos for a much more murderous example.

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Egg-like glands at the base of the passionflower leaf (the white dots on my index finger).

Had the passionflowers in this example been a clonal species, they wouldn’t likely have stood a chance. Innovations such as higher-than-average levels of cyanide or slightly more bulbous nectar glands upon which defences can be built come from uncommon genotypes. Uncommon genotypes produced by the shuffling of genes that occurs in every generation in sexual species.

And that, kids, is why sex is such as fantastic innovation. (Right?) Every time an illness goes through your workplace, and everybody seems to get it but you, you’ve probably got the Red Queen (and your uncommon genotype) to thank.

 

Sources

  • Brockhurst et al. (2014) Proc. R. Soc. B 281: 20141382.
  • Lively (2010) Journal of Heredity 101 (supple.): S13-S20 [See this paper for a very interesting full explanation of this links between the Red Queen hypothesis and the story by Lewis Carroll.]
  • Vanderplank, John. “Passion Flowers, 2nd Ed.” Cambridge: MIT Press, 1996.

*The illustration at the top of the page is by Sir John Tenniel for Lewis Carroll’s “Through the Looking Glass,” and is now in the public domain.

Floral Invasion

Onam_Flower_Arrangement            Throughout evolution, there have been, time and time again, key biological innovations that have utterly changed history thereafter. Perhaps the most obvious is the one you’re using to read this; the human brain. The development of the anatomically modern human brain has profoundly changed the face of the planet and allowed humans to colonize nearly every part of the globe. But an equally revolutionary innovation from an earlier time stares us in the face each day and goes largely unremarked upon. Flowers. (Stay with me here, guys… ) We think of them as mere window dressing in our lives. Decorations for the kitchen table. But the advent of the flowering plants, or “angiosperms”, has changed the world profoundly, including allowing those magnificent human brains to evolve in the first place.

 

Angiosperm percentage
From: Crepet & Niklas (2009) Am. J. Bot. 96(1):366-381

Having arisen sometime around the late Jurassic to early Cretaceous era (150-190 million years ago), angiosperms come in every form from delicate little herbs to vines and shrubs, to towering rainforest canopy trees. They exist on every continent, including Antarctica, which even humans have failed to develop permanent homes on, and in every type of climate and habitat. They exploded from obscurity to the dominant form of plant life on Earth so fast that Darwin himself called their evolution an “abominable mystery”, and biologists to this day are unable to nail down exactly why they’ve been so incredibly successful. Nearly 90% of all terrestrial plant species alive today are angiosperms. If we measure success by the number of species that exist in a given group, there are two routes by which it can be improved- by increasing the number of distinct species (“speciation”), or by decreasing the rate at which those species go extinct. Let’s take a look at a couple of the features of flowers that have likely made the biggest difference to those metrics.

Picture a world without flowers. The early forests are a sea of green, dominated by ferns, seed ferns, and especially, gymnosperms (that is, conifers and other related groups). Before the angiosperms, reproduction in plants was a game of chance. Accomplished almost exclusively by wind or water, fertilization was haphazard and required large energy inputs to produce huge amounts of spores or pollen grains in order that relatively few would make their way to the desired destination. It was both slow and inefficient.

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The world before flowers. By Gerhard Boeggemann on Wikimedia Commons

The appearance of flowers drew animals into the plant reproduction game as carriers for pollen – not for the first time, as a small number of gymnosperms are known to be insect pollinated – but at a level of control and specificity never before seen. Angiosperms have recruited ants, bees, wasps, butterflies, moths, flies, beetles, birds, and even small mammals such as bats and lemurs to do their business for them. The stunning variety of shapes, sizes, colours, and odours of flowers in the world today have arisen to seduce and retain this range of pollinators. Some plant species are generalists, while others have evolved to attract a single pollinator species, as in the case of bee orchids, or plants using buzz pollination, in which a bumblebee must vibrate the pollen loose with its flight muscles. In return, of course, the pollinators are rewarded with nectar or nutritious excess pollen. Or are at least tricked into thinking they will be. Angiosperms are paying animals to do their reproductive work for them, and thanks to incentivisation, the animals are doing so with gusto. Having a corps of workers whose survival is linked to their successful pollination has allowed the flowering plants to breed and expand their populations and territory quickly, like the invading force they are, and has lowered extinction rates in this group well below that of their competitors. But what happens when you expand into new territory to find that your pollinators don’t exist there? Or members of your own species are simply too few and far between for effective breeding?

Selfing morphology
On the left, a typical outbreeding flower. On the right, a selfing flower of a closely related species. From: Sicard & Lenhard (2011) Annals of Botany 107:1433-1443

Another unique feature that came with flowers is the ability to self-fertilise. “Selfing”, as it’s called, is a boon to the survival of plants in areas where pollinators can be hard to come by, such as very high latitudes or elevations; pollen simply fertilises its own flower or another flower on the same plant. Selfing can also aid sparse populations of plants that are moving into new territories, since another of its species doesn’t need to be nearby for reproductive success. It even saves on energy, since the flower doesn’t have to produce pleasant odours or nectar rewards to attract pollinators. Around half of all angiosperms can self-fertilise, although only 10-15% do so as their primary means of reproduction. Why, you may ask, since it’s such an effective strategy? Well, it’s an effective short term strategy. Because the same genetic material keeps getting reused, essentially, in each successive generation (it is inbreeding, after all), over time the diversity in a population goes down, and harmful mutations creep in that can’t be purged via the genetic mix-and-match that goes on in normal sexual reproduction. Selfing as a sole means of procreation is a slow ticket to extinction, which is why most plants that do it use a dual strategy of outbreeding when possible and inbreeding when necessary. As a short term strategy, however, it can allow a group of new colonists to an area to survive long enough to build up a breeding population and, in cases where that population stays isolated from the original group, eventually develop into a new species of its own. This is how angiosperms got to be practically everywhere… they move into new areas and use special means to survive there until they can turn into something new. I’m greatly simplifying here, of course, and there are additional mechanisms at play, but this starts to give an idea of what an unstoppable force our pretty dinnertable centrepieces really are.

Angiosperms are, above all, adaptable. Their history of utilising all possible avenues to ensure reproductive success is unparalleled. As I mentioned, we have the humble flower to thank for our own existence. Angiosperms are the foundation of the human – and most mammal – diets. Both humans and their livestock are nourished primarily on grasses (wheat, rice, corn, etc.), one of the latest-evolving groups of angiosperms (with tiny, plain flowers that you barely notice and which, just to complicate the point I’m trying to make here, are wind-pollinated). Not to mention that every fruit, and nearly every other type of plant matter you’ve ever eaten also come from angiosperms. They are everywhere. So the next time you buy flowers for that special someone, spare a moment to appreciate this world-changing sexual revolution in the palm of your hand.

Sources

  • Armbruster (2014) AoB Plants 6: plu003
  • Chanderbali et al. (2016) Genetics 202: 1255-1265
  • Crepet & Niklas (2009) American Journal of Botany 96(1): 366-381
  • Endress (2011) Annals of Botany 107: 1465-1489
  • Sicard & Lenhard (2011) Annals of Botany 107: 1433-1443
  • Wright et al. (2013) Proc. Biol. Sci. 280(1760): 20130133

**Top image by Madhutvin on Wikimedia Commons **

Bee_Orchid_(Ophrys_apifera)_(14374841786)_-_cropped
Photo by Bernard Dupont on Wikipedia

Pitcher Plants: Sweet Temptation and the Slippery Slope

(Via: Wikimedia Commons)

Common Name: The Asian Pitcher Plant

A.K.A.: Genus Nepenthes

Vital Stats:

  • Over 130 species in the genus
  • The vast majority of species have extremely narrow ranges of only a single island or small island group, and are considered threatened
  • Most recently discovered (2007) was Nepenthes attenboroughii, named for Sir David Attenborough, who is fond of pitcher plants

Found: Mountainous regions of Southeast Asia, Oceania, and Madagascar

It Does What?!

Plants have evolved a variety of different ways to deal with growing in nutrient-poor soils. Some become parasitic, some develop close symbiotic relationships with bacteria or fungi, and some of them… well, some of them just start eating animals.

Lizard: makes a nice, light snack.
(Via: Wikimedia Commons)

One group of plants that went this route are the Asian pitcher plants (not to be confused with the not-closely-related New World pitcher plants, which tend to have tall, flute-like pitchers). These smallish, climbing plants use highly modified leaves to form what are essentially external stomachs, complete with the plant’s own digestive fluid. These pitchers, which vary in size from one species to the next, have extremely slick, waxy inner walls. When visitors come to eat the nectar produced on the lid (or “operculum”) of the trap, they lose their footing and fall into the liquid below.

That liquid is actually a pretty complex mixture; it’s divided into two phases, like oil and water. The upper portion is mostly rainwater, but has been laced with a compound that makes it more viscous, preventing winged insects from just flying away, as they could from pure water. The trap’s lid actually functions to prevent too much rainwater from getting inside and diluting the fluid too much. The lower portion of the liquid is a digestive acid capable of breaking down flesh into useable molecules (particularly nitrogen and phosphorous), much like our own stomach acid. Analogous to our intestines, the lower inside surface of the pitcher is covered with special glands that absorb suspended nutrients.

Most of what gets caught in pitcher plants is about what you’d expect- winged insects, spiders, beetles, small scorpions. But occasionally, some larger animals find their way in. Things that should have known better, like frogs, lizards, and even birds. Arguably, these plants are doing evolution a favour by taking out any bird dumb enough to fly into its own watery grave. And yes, to answer your next question- they can eat rats, but only a single species has been documented to do this. Nepenthes rajah, the largest of all pitcher plants, has pitchers which grow to a height of nearly half a metre (1.6’) and hold up to three and a half litres (1gal.) of fluid, most of which is digestive juice.

Interestingly, pitcher plants have formed symbiotic relationships with several of the same types of creatures that it otherwise preys on. Nepenthes lowii, for example, provides nectar to a tree shrew. Instead of falling in and being digested, the shrew treats the pitcher as its personal toilet, thereby providing the plant with most of the nutrition it requires.

In one end and out the other.
(Via: Wikimedia Commons)

Other species form alliances with groups of carpenter ants. In exchange for a steady supply of nectar and a place to live- in this case a hollow tendril- the ants basically act as the plant’s evil henchmen (apparently a specialty of ants). When prey that is too large to be easily digested falls into the trap, the ants remove it, rip it to shreds, and then throw the bits back in again.

How’s that for a brilliant piece of evolution? Not only did these plants grow an external stomach… they get ants to chew their food for them.

[Fun Fact: Some pitcher plants primarily survive by digesting leaves that fall from trees into their traps – the ‘vegetarians’ of the carnivorous plant world.]

Says Who?

  • Bonhomme et al. (2011) Journal of Tropical Ecology 27: 15-24
  • Clarke et al. (2009) Biology Letters 5: 632-635
  • Krol et al. (2012) Annals of Botany 109: 47-64
  • Robinson et al. (2009) Botanical Journal of the Linnean Society 159: 195-202
  • Wells et al. (2011) Journal of Tropical Ecology 27(4): 347-353
So big it makes them vaguely uncomfortable.
(Via: Wikimedia Commons)

The Stench of Death, brought to you by the Forests of Sumatra

(Via: The Parasitic Plant Connection)

Common Name: Giant Rafflesia

A.K.A.: Rafflesia arnoldii

Vital Stats:

  • One of about 28 species of Rafflesia, all parasites native to southeast Asia
  • Dioecious: produces male and female flowers on separate plants
  • Flowers last only a few days

Found: In the rainforests of Sumatra, Western Indonesia

It Does What?!

In my very first post here on Questionable Evolution, I discussed the Titan Arum, a.k.a. Corpse Plant, known for its pungent aroma and generally phallic appearance. This rare oddity is confined to the ever-shrinking rainforests of the western Indonesian island of Sumatra. Now meet its neighbour and fellow rotting flesh imitator, the Giant Rafflesia. Like the Titan Arum, this species is found only in the Sumatran rainforest and uses its odour to attract carrion flies for pollination. (With all the plants pretending to be dead animals on this island, it’s a wonder the flies ever actually find themselves any real carcasses.)

How big?  THAT big.
(With Mr. Troy Davis, Via: The Parasitic Plant Connection)

Rafflesia’s claim to fame in the plant world is that it produces the largest flower on Earth. A single bloom from Rafflesia arnoldii can reach a diameter of 1m (3.3’) and a mass of up to 7kg (15lbs.). In other words, one flower weighs about as much as your overweight cat. Impressive, sure, but what’s more interesting about this plant is that the flower’s the only part of it you’re ever likely to see.

Much like dodder, rafflesia is a holoparasite, depending entirely on a host plant (in this case, a vine of genus Tetrastigma, part of the grape family) for its water and nutrients. Unlike dodder, however, rafflesia doesn’t grow up and over its victim, eventually smothering it- no, this plant grows inside its host. Over the course of its evolution, the leaves, roots, and stems of rafflesia have been reduced to nothing but miniscule threads that grow, fungus-like, through the intercellular spaces of another plant, absorbing whatever they require. The giant flower arises directly from the roots or stem of the host vine, pushed out through the host’s tissues. Think chestbursters from Alien. Beyond the juvenile phase when a new seedling searches for its host, this is the only part of rafflesia that will ever see the light of day.

Flowering Time!!

Interestingly, botanists have found that rafflesia’s giant flowers evolved over a very short period of time (relatively speaking), with flower diameter increases of, on average, 20cm per million years. Blindingly fast, as plant evolution goes. The reason for this, they speculate, may have been a preference on the part of certain carrion flies to feed on larger animal carcasses. The range of flower sizes seen in different species of genus Rafflesia probably functions to attract different sets of fly species with varying tastes – some want wee little dead mice, some want dead rhinoceros, judging from the size of these things.

Plants: give ‘em a few million years, and they can mimic almost anything.

Says Who?

  • Barkman et al. (2008) Current Biology 18: 1508-1513
  • Beaman et al. (1988) American Journal of Botany 75(8): 1148-1162
  • Patifino et al. (2002) New Phytologist 154: 429-437

EVOLUTION TAG TEAM, Part 3: Coral Polyps & the Garden Within

The third in an ongoing series of biology’s greatest duos. (Check out Parts One and Two)

(Via: Wikimedia Commons)

Common Name: Coral Polyps

  • A.K.A.: Class Anthozoa, Subclass Hexacorallia

Common Name: Coral Algae

  • A.K.A.: Genus Symbiodinium

Vital Stats:

  • Polyps grow to a length of only a few centimetres, depending on species
  • Coral can grow outward at a rate of up to 10cm (4”) per year
  • The Great Barrier Reef stretches over 2000km (1243 mi) and can be seen from space

Found: Various coastal areas; largest reefs surrounding Australia, Oceania, and the Caribbean

It Does What?!

If you’ve ever been told that coral reefs are alive, then looked at one and felt a bit sceptical that this chuck of colourful rock could be a living thing… well, good for you, because you’re actually mostly right. The vast majority of the volume of a coral reef is, in fact, nonliving inorganic mineral (calcium carbonate, specifically). The amazing thing about coral isn’t so much what it’s made of, but what’s going on on the surface. You see, that oddly-shaped, porous rock is actually a communal exoskeleton produced and excreted over time by hundreds of thousands of polyps living in the tiny, cup-shaped depressions on the surface.

“Breaded, with a side of chips, please.”
(Via: Wikimedia Commons)

Looking like tiny jellyfish (and belonging to the same phylum), the polyps hide in the stony sanctuary they’ve made, letting only their tentacles project. These tentacles are tipped with stinging cells which can inject a powerful venom into any prey foolish enough to swim within reach. This prey can range in size from microscopic plankton to small fish. That’s right, coral eats fish. Watch where you stick your toes.

So where does the ‘duo’ part come in? Despite their ability to snatch passing sea creatures and eat them, coral polyps actually get only a small part of their caloric intake this way. Impressively, these guys managed to find a diet that requires even less effort than just reaching out and grabbing stuff. Who needs movement when you can just photosynthesize, like plants do? The polyps have developed a symbiosis with a type of single-celled alga (called zooxanthellae) that allows them to do just that.

The algae start out as free-living cells drifting through the water. They are eaten by the coral polyp, but instead of being digested, they are able to enter the cells lining its digestive tract. Since the polyps are transparent to begin with, all they have to do is expose their bodies to sunlight in order to allow the algae to produce sugars by photosynthesis (this is why reefs form in relatively shallow waters). The majority of the sugars made by the symbiont are then absorbed by the polyp.

And what do the algae get out of this arrangement? A couple of things. First, they get a safe place to live, and won’t get eaten by something that can digest them. Second, they get nutrients, in the form of carbon dioxide and nitrogen compounds, both natural waste products of the polyp’s metabolism. Still, sometimes as much as 30% of the cells in a polyp are algal cells, and this puts a stain on the host’s physiology.

“I’ve just got a lot going on right now.”
(Via: Wikimedia Commons)

Maybe you’ve heard of “coral bleaching” as one of the symptoms of pollution around reefs. Bleaching happens when additional stresses (like pollution) get to be a bit too much for the polyps to handle. They can’t change the water purity, so instead, they offload the stressor they can control- the algae. Getting rid of the photosynthetic cells also gets rid of much of the characteristic colour of the reef, hence the term ‘bleaching’. In the short term, this is a smart move. It increases the polyp’s chance of survival during brief crises, and new algae can always be taken on when the host is ready. The real problems start when the environmental stress persists, and the polyp never takes on new algae. Eventually, it can’t sustain itself and dies, as those in a tenth of the world’s reefs already have. At least there’s still hope for these areas; if conditions improve, new colonies can be formed using the old reef as a foundation. The Great Barrier Reef, for example, is considered to be between 6000 and 8000 years old. However, the modern structure has developed atop an older, dead reef system, thought to be over half a million years old. Time enough for us to clean up our act, maybe.

[Fun Fact: Coral polyps only reproduce sexually to start new colonies. Within a single piece of coral, all the polyps are genetically identical clones, produced by polyps dividing in half and then re-growing their lost tissues.]

Says Who?

  • CoRIS- Coral Reef Information System
  • Fransolet et al. (2012) Journal of Experimental Marine Biology and Ecology 420-421:1-7
  • Piper (2007) Extraordinary Animals. Greenwood Press: Westport, Connecticut.
  • Wooldridge (2010) BioEssays 32(7):615-625

    The little-known “Lady Gaga Coral”
    (Via: Wikimedia Commons)

The Plant That Time Forgot (Welwitschia mirabilis)

(Via: Wikimedia Commons)

Common Name: Welwitschia mirabilis

A.K.A.: Welwitschia

Vital Stats:

  • Welwitschia is a gymnosperm, like pines or firs, and thus reproduces via male and female cones
  • Considered a “living fossil”
  • Named after one of its discoverers, Austrian botanist Friedrich Welwitsch
  • In mature specimens, the woody stem can grow up to one metre (3.3’) across

Found: In the Namib desert, along the west coast of Namibia and Angola

It Does What?!

Restricted to a tiny, arid swath of African desert, Welwitschia mirabilis represents the last remaining species of a very unusual lineage of plants. Close relatives met with extinction over the aeons, while welwitschia, tucked away in its remote and harsh desert range with little competition, just kept going. The fact that the species is alone, not just in its genus, but also in its family and order (the two ranks above genus in plant systematics), speaks to just how distantly related to any other living plant it is. For the sake of comparison, the Rosales, the order to which roses, apples, and pears belong, contains around 7700 species in 9 families and 260 genera. So original and captivating is welwitschia among plants that it has been the subject of more than 250 scientific articles since it was first described in 1863.

A mere infant. But probably still older than you are.
(Via: Lizworld.com)

So what makes this thing so weird? Well, plants typically have what’s called an apical meristem at the tips of their stems and/or branches. You can think of this as a clump of stem cells that keeps dividing, throwing off new leaves and buds in its wake. If you cut off the apical meristem, the plant must either develop a new one elsewhere, or stop producing new tissue.

In welwitschia, this isn’t the case. At the beginning of the plant’s life, the apical meristem produces just two leaves, and then dies. The plant will never grow another leaf, which is much more surprising when you consider that it may well live for more than a thousand years. How do you get through a millennium with only two leaves?! The answer is, these aren’t ordinary leaves. Uniquely, welwitschia’s two strap-like leaves have a band of meristematic tissue built into their base, which means they can continue to elongate outward indefinitely. The leaves will continue to grow at a rate of around half a millimetre (0.02”) per day for as long as the plant lives. If you’re thinking that this must mean leaves that are several hundred metres long, unfortunately, no, they aren’t. The leaves are abraded away by sand storms and eaten by passing animals. Even in the best case scenario, the cells at the leaf tips have a maximum lifetime of about ten years (still pretty good for a leaf…). What’s more, the leaves tend to get frayed and split over time, and end up looking like a lot more than just two leaves. Despite all the punishment, though, each leaf can reach a length of up to four metres (13’), giving a mature welwitschia a width of up to eight metres (26’) across.

Welwitschia’s answer to the pinecone.
(Image by Friedrich A. Lohmuller)

As you might expect from a long-lived relic of the past, there aren’t a lot of these plants around. For once, this has less to do with human disturbance than natural circumstances. Over millions of years, the range where welwitschia grows has dried out considerably, and in fact continues to get drier even now. Today, the plant relies largely on fog to meet its water needs, restricting its range to a thin strip of desert coastline where fogs occur regularly. Unlike cactuses or succulents, welwitschia has never evolved the ability to store water. Also problematic is a fungus, Aspergillus niger, which frequently infects and destroys germinating seeds. These factors together can mean that a welwitschia colony can sometimes go many years without successfully reproducing.

And of course, no threatened species would be complete without some human interference. In recent decades, unscrupulous collectors have removed plants from already small breeding populations, making it even more difficult to sustain their numbers. Interestingly, it’s noted in Wikipedia that plants in Angola are actually better protected from collecting than those in Namibia due to the higher concentration of landmines there.

So… landmines: bad for humans, good for endangered plants.

You think you have problems with split ends?
(Via: Natural History Museum)

Says Who?

  • The Gymnosperm Database
  • Dilcher et al. (2005) American Journal of Botany 92(8):1294-1310
  • Henschel & Seely (2000) Plant Ecology 150:7-26
  • Jacobson & Lester (2003) Journal of Heredity 94(3):212-217
  • Rodin (1958) American Journal of Botany 45(2):96-103