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What’s in a Name?

Part Two: How’s Your Latin?

295738_obamadon_f
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.

acacia
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!

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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.

 

Toxicodendron_vernix#1978a#2_400
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.

 

1024px-Spanish_moss_at_the_Mcbryde_Garden_in_hawaii
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

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Sex & the Reign of the Red Queen

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.

1280px-Passiflora_in_Canary_Islands
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.

IMG_2933
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.

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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.

1280px-Europasaurus_holgeri_Scene_2
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
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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)
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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
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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)
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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
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Killing Me Softly, or, The Fatal Embrace of the Strangler Fig

(Via: Wikimedia Commons)

Common Name: Strangler Figs

A.K.A.: Ficus species

Vital Stats:

  • There are around 800 sp. of figs, over half of which are hemi-epiphytes, like stranglers
  • Around 10% of all vascular plants are epiphytes (about 25,000 species)
  • The trees which produce the figs we eat are terrestrial, and do not grow in other trees

Found: Tropical forests of Latin America, Southeast Asia, and Australia

It Does What?!

What does it take to squeeze the life out of a full-grown tree? A lot of time and some very long roots, apparently. Many parasites eventually bring about the untimely death of their hosts, but few do it as slowly and as insidiously as the strangler fig.

Stranglers begin life as a tiny seed that leaves the back end of a bird and happens to land on a tree branch high in the rainforest canopy. The seed germinates, and the young fig begins to grow as an aerial plant, or epiphyte, taking its moisture from the air and its nutrients from the leaf litter on its branch. Thousands of plant species, including most orchids, grow in this manner. But then an odd thing begins to happen. The seedling produces a single long root. Very long. From tens of metres up in the canopy, this root grows all the way down to the ground. Many young stranglers will die before their questing root reaches the earth, but for those that make it, a connection is formed with the soil through which water and nutrients can be extracted. From this point on the great, towering giant which holds this tiny little interloper is in mortal danger.

The strangler fig, playing “harmless epiphyte.”
(Screenshot from The Private Life of Plants, BBC)

A secure connection to the soil allows the fig to speed up its growth and to begin sending more and more roots earthward. Rather than dropping straight down, like the initial root, these later organs will twine around the bark of the host tree. At first, the roots are tiny, like mere vines crawling over the host trunk. Over time, however, they thicken, covering more and more of the trunk’s surface. Where they touch or overlap, the roots actually fuse together, forming a mesh over the surface of the bark. Up above, the stem of the strangler is growing as well. It rises through and above the host branches, soaking up the light and leaving the other tree shaded and starved for energy.

In fact, this is a war fought on two fronts. As the starving host tree struggles to gather light energy to send downward from the leaves, it is also increasingly unable to bring water up from its roots. This is because the tree’s trunk continues to expand even as the strangler’s grip grows tighter around it. These opposing forces effectively girdle the tree, crushing the vascular tissues that carry moisture from the soil. Eventually, the battle is lost and the tree dies. Fortunately for the fig, its major investments in root growth have paid off – the dead host tree does not fall, taking the strangler with it. Instead, it simply rots where it stands. Finally, many years after its arrival on the scene, the strangler fig has achieved independence. It is now a free-standing tree, completely hollow and supported by its interwoven lattice of aerial roots.

The first root finds the ground.
(Screenshot from The Private Life of Plants, BBC)

So what happens when more than one strangler fig seed lands on a particular tree? Something quite unique… the roots of the different individuals fuse and form an organism which is indistinguishable from a single tree, except by molecular testing. These are what biologists refer to as ‘genetic mosaics.’ What’s more, the individuals actually begin to act like a single tree. You see, figs typically have staggered flowering times, such that it is unlikely for numerous trees in a small area to be in bloom at the same time. This helps in keeping their wasp symbionts well nourished. Once trees fuse, however, they seem to become physiologically linked as well, with researchers reporting that they bloom as a single individual.

The most hurricane-proof tree ever.
(Screenshot from The Private Life of Plants, BBC)

[Fun Fact: Some strangler fig species have very high growth rates, and huge individuals have actually been found engulfing abandoned buildings in the tropics.]

Says Who?

  • Harrison (2006) Journal of Tropical Ecology 22(4): 477-480
  • Perry & Merschel (1987) Smithsonian 17: 72-79
  • Schmidt & Tracey (2006) Functional Plant Biology 33: 465-475
  • Thomson et al. (1991) Science 254: 1214-1216
Don’t meditate under strangler figs.
(Via: Flickr, by vincenzooli)
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The Bloodhounds of the Plant World (Cuscuta sp.)

(Via: Marine Science)

Common Names: Dodder, Goldthread, Witch’s Shoelaces

A.K.A.: Genus Cuscuta

Vital Stats:

  • Approximately 200 species
  • Part of the Convolvulaceae family, which includes morning glory and sweet potato
  • Only 15-20 species are considered to be problematic crop parasites

Found: Throughout temperate and tropical parts of the world

It Does What?!

We’ve discussed a few parasites on this blog already, and they’ve all been pretty typical of what comes to mind when we think of parasitic organisms- tiny, malignant little creatures that invade the host’s body, steal its resources, and, in some cases, eat its tongue. But when we think ‘parasite,’ we don’t usually think ‘plant.’ As it turns out, there are an estimated 4500 parasitic species just among the angiosperms, or flowering plants. Among them, dodders have to be one of the strangest.

Found nearly throughout the world, these vine-like plants begin as tiny seeds that germinate late in the spring or summer, after their potential host plants have established themselves. The young seedling has no functional roots and little or no ability to photosynthesize, so initially, it must make do with what little nutrition was stored in its seed. This isn’t much, so the plant has only a few days to a week to reach a host before it dies. To better its chances, the dodder stem swings around in a helicopter-like fashion as it grows, trying to hit something useful.

Much more impressive is the plant’s other method of finding suitable hosts- a sense of smell. Recent research has found that, uniquely among plants, the dodder can actually detect odours given off by surrounding plants and grow towards them. In experiments, the seedlings were found to grow toward the scent of a tomato, even if no actual plant was present. What’s more, they are capable of showing a preference among hosts. Presented with both tomato plants, which make excellent hosts, and wheat plants, which make poor hosts, seedlings were found to grow toward the aroma of tomatoes much more often. Like herbivores, they can use scent to forage amongst a variety of species for their preferred prey.

Smells like lunch… even to other plants.
(Via: Wikimedia Commons)

Once a host plant is found, the dodder begins to twine itself around the stem and to form haustoria (singular: haustorium). These are like tiny tap roots that pierce the host’s stem and actually push between the living cells inside until they reach the vascular system. Once there, the haustoria enter both the xylem (where water and minerals move upward from the roots) and the phloem (where sugars from photosynthesis move around the plant). From these two sources, the dodder receives all its nutrients and water, freeing it from any need for a root system, or even a connection to the soil. And since it doesn’t need to capture solar energy, all green pigment fades from the parasite, and it turns a distinctive yellow or red colour. Leaves aren’t necessary either, which is why the plant is essentially nothing but stem, explaining its common name of “witch’s shoelaces.”

Not what you want to see when you head out to weed the garden.
(Via: County of Los Angeles)

Once it gets comfortable on its new host, the dodder can grow at a rate of several centimetres a day (impressive for a plant) and produce stems of a kilometre or more in length, quickly overrunning an area. It can also attach itself to additional hosts – hundreds, in fact – which is problematic, because at this point it becomes the plant equivalent of a dirty shared needle. Since the vasculature of the hosts is connected, any virus present in one host can be freely transferred to any other. This ability, coupled with its affinity for potatoes, tomatoes, tobacco, and several other important crops, makes dodder a major nuisance for many farmers. And since it’s able to regenerate from just a single, tiny haustorium left in a host plant, it’s really hard to get rid of. There’s always a flip side, though; in some ecosystems, dodder can actually maintain biodiversity by preferentially parasitising the more competitive plants, allowing the weaker ones to survive. It seems dodder may also be the Robin Hood of the plant world.

[Extra Credit: Here’s a video showing how dodder can completely take over a group of nettle plants, complete with ominous soundtrack. Narrated by the fantastic Sir David Attenborough.]

Says Who?

  • Costea (2007-2012) Digital Atlas of Cuscuta (Convolvulaceae). Wilfred Laurier University Herbarium, Ontario, Canada
  • Furuhashi et al. (2011) Journal of Plant Interactions 6(4): 207-219
  • Hosford (1967) Botanical Review 33(4): 387-406
  • Pennisi (2006) Science 313: 1867
  • Runyon et al. (2006) Science 313:1964-1967

    Cuscuta: 1, Acacia: 0
    (Via: Wikimedia Commons)