Monday, February 22, 2016
Evolution doesn't always tend towards larger, more complex organisms. The dinosaurs' closest living relatives are pigeons and sparrows. Similarly, the tiny, shy aquatic quillworts (Isoetes) descend from "scale trees" that dominated great rainforests 300 million years ago and could've outgrown a 9-story building.
From dinosaur to chicken: Isoetes and its ancestors
Today, the closest living relative of Tyrannosaurus rex is arguably a chicken.
All right, that isn't strictly true: birds are certainly the closest living relatives of dinosaurs (and are in fact dinosaurs themselves, by any reasonable measure), but chickens are no closer to T. rex than are swans, ostriches, or toucans. They're also no more distantly related than any of those, though -- and isn't that remarkable? Goofy, awkward, halfway-flightless domesticated featherbags have as much claim to the tyrannosaur's legacy as anything else alive.
Evolution does this sort of thing all the time, altering species in directions quite different from any human notion of "progress." The plant kingdom has hundreds of examples, and none quite as spectacular as the story of Lepidodendron and Isoetes.
An extinct genus of giant lycopsids (early ferns) with thick scale-patterned bark and leafy, forking branches, Lepidodendron -- the scale trees -- once dominated great rainforests that stretched around the world. Despite having no true wood to hold them up, they grew up to 30 meters tall with trunks a meter thick. For sixty million years, they flourished worldwide. Their rainforests produced so much plant matter that instead of decaying or fossilizing normally, it compacted into vast beds of coal. Huge scale-tree fossils -- massive trunks, spiky-leaved branches, sporing cones longer than a human hand -- have captured botanists' imagination for as long as miners have been chipping them free of the bedrock. It's no exaggeration to call these vanished giants the Tyrannosaurus of the plant world.
300 million years ago, though, the scale trees went extinct. The Carboniferous ended in a planetary cold snap that brought glaciers creeping down from the poles; practically overnight, the rainforests collapsed. Giant lycopsids all but vanished, and tree ferns took their place in the cold new forests.
Today, Lepidodendron's closest living relatives are the little grass-like quillworts of the genus Isoetes. They're tiny compared to their ancestors: a quillwort 20 cm tall is quite unusual, and the largest species alive only grow to one meter. Their rolled-up, rush-like leaves don't look much like scale-tree branches, and they have nothing at all like bark. They keep their spores tucked close inside the base of the leaves; there is no separate sporing cone. Most of them are aquatic, growing in calm freshwater. The North American species are particularly good at surviving in cold, infertile lakes where little else will grow.
These pointy little proto-ferns look about as much like the great Lepidodendron as a chicken resembles Tyrannosaurus. Just like the chicken, though, there are similarities: the structure of their veins, their different male and female spores, and the history traced in their genes. It's all there, if you can find the right way to see. Inside every quillwort is the shadow of an ancient rainforest.
Image sources:
All right, that isn't strictly true: birds are certainly the closest living relatives of dinosaurs (and are in fact dinosaurs themselves, by any reasonable measure), but chickens are no closer to T. rex than are swans, ostriches, or toucans. They're also no more distantly related than any of those, though -- and isn't that remarkable? Goofy, awkward, halfway-flightless domesticated featherbags have as much claim to the tyrannosaur's legacy as anything else alive.
Evolution does this sort of thing all the time, altering species in directions quite different from any human notion of "progress." The plant kingdom has hundreds of examples, and none quite as spectacular as the story of Lepidodendron and Isoetes.
 |
| Artist's reconstruction of Lepidodendron. This one was as tall as a 9-story building. |
300 million years ago, though, the scale trees went extinct. The Carboniferous ended in a planetary cold snap that brought glaciers creeping down from the poles; practically overnight, the rainforests collapsed. Giant lycopsids all but vanished, and tree ferns took their place in the cold new forests.
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| A clump of Isoetes tegetiformans with a U.S. penny for scale. Not much to look at unless you know what to look for. |
These pointy little proto-ferns look about as much like the great Lepidodendron as a chicken resembles Tyrannosaurus. Just like the chicken, though, there are similarities: the structure of their veins, their different male and female spores, and the history traced in their genes. It's all there, if you can find the right way to see. Inside every quillwort is the shadow of an ancient rainforest.
Image sources:
- Heimans, Eli. "Stigmaria [Lepidodendron] reconstruction." Retrieved 20 Feb 2016 from Wikimedia Commons: <https://en.wikipedia.org/wiki/File:Stigmaria_Heimans.jpg>
- US Fish and Wildlife Service. "Isoetes tegetiformans, on granite outcrop in eastern half of Georgia Piedmont." Retrieved 20 Feb 2016 from Wikimedia Commons: <https://commons.wikimedia.org/wiki/File:Isoetes_tegetiformans.jpg>
Friday, February 19, 2016
Life after extinction: Ginkgo biloba
The ginkgo tree, Ginkgo biloba, is well-known and highly distinctive. Its elegant fan-shaped leaves and oddly knobbly twigs make it easily recognizable all year round; its stately silhouette and general beauty make it quite popular in temperate cities' landscaping. Its cherrylike seeds are edible, as long as you discard the foul-smelling flesh before eating the nut, and have a long history of use in traditional Chinese medicine. The tree is sacred to several Buddhist traditions as a symbol of long life.
It should also, by all rights, be extinct.
Ginkgo biloba is the very last of its line. Back in the Jurassic period, there were dozens, maybe hundreds, of ginkgo species: entire fossil strata are positively saturated with their leaves. With the explosive rise of the flowering plants, though, the ginkgoes went into decline and fell one by one to extinction. When humans finally came on the scene, there was only one species left, and it was fading fast.
Fortunately for that elegant relic, though, humans decided that we really, really liked it. For its symbolism, Japanese Buddhist monks planted the trees on their monastery grounds and tended them lovingly even as their wild sisters faded. About a thousand years ago, the last of the wild ginkgoes died out, and those monastery trees became the last of their species.
Today, ginkgoes are planted along streets and in parks and lawns all over the world. Every one of them is descended, recently or farther back, from one of those rescued monastery trees. They are living proof that humans have the capacity to save species as well as destroy them.
Tuesday, October 7, 2014
Photosynthesis was scary stuff.
I dare say most of us don't think of plants as particularly dangerous things. Sure, some of them are poisonous, but you generally have to eat them first. A few will give you a nasty rash. Some even eat animals. Unless you're actively interacting with them, though, there's not much they can do to you.
As it turns out, they've already done their worst... and their worst was photosynthesis.
It's worse than it sounds, believe me, and here's why. Let's imagine for a minute that a new species of organism evolved today, one with a really exotic metabolism -- one that, where you and I take in oxygen and release carbon dioxide, took in our familiar air and released hydrogen fluoride. As the article behind that link describes, hydrogen fluoride is truly vicious stuff -- it's violently corrosive and extremely toxic, the kind of acid that dissolves glass outright and kills you with acute fluoride poisoning if the horrid chemical burns don't do it first.
Now imagine that this organism succeeded. Really succeeded. It spread all over the planet. Its breath corroded the very ground it lived on, and now there was a lot of it -- enough to burn off the entire surface of the earth. It wouldn't stop when the soil was seared away and the rocks saturated with fluoride, either: those things would still be alive, and still spitting their poison, only now it'd be building up in the air. In a geological eyeblink, they'd choke the entire atmosphere with toxic acid. I'm not going to describe exactly what would happen to life on Earth in that situation, but you can probably fill in the blanks yourself.
That's what happened when photosynthesis first arose.
When the earth was young, and life was just getting started, there was virtually no oxygen in Earth's atmosphere. Free O2 is reactive stuff; it had all gotten bound up in carbon dioxide. The atmosphere of the time was mostly nitrogen and CO2. Early life on Earth had evolved to be comfortable in that environment; to those early species, oxygen was a corrosive metabolic poison -- much like, say, hydrogen fluoride is to us.
Then, about 2.5 billion years ago, the first photosynthetic organisms evolved. They were something like cyanobacteria -- blue-green algae -- and probably not very efficient by modern standards, but they succeeded, and they started cranking out oxygen by the ton. At first it just corroded the rocks, oxidizing them quickly and thoroughly; those first blue-green algae literally rusted the entire planet, and when the rocks were saturated, they started poisoning the atmosphere.
We have no way of knowing what the death toll was like, as free oxygen built up towards the modern 20% or so -- hard skeletons hadn't evolved yet, so nothing much from that era ever fossilized -- but it was assuredly unimaginable. This Oxygen Catastrophe was the first of Earth's great mass extinctions, and it made the slaughter of the dinosaurs look like barely a blip.
Mercifully, it never happened again. The few species that survived the Oxygen Catastrophe learned to work with free oxygen; aerobic respiration actually turned out to be pretty effective. The staggering diversity of life today is all descended from those survivors.
...Well, it never happened again, until very, very recently. Just an evolutionary eyeblink ago, another species with the ability to transform its whole world's atmosphere arose. It spread across the globe. It started cranking out its chosen gases in geologically-significant quantities. Just now, some individuals have even begun to notice what their species is doing. Some of them are taking steps toward making it stop.
Makes you think twice about how scary climate change might be, doesn't it?
As it turns out, they've already done their worst... and their worst was photosynthesis.
It's worse than it sounds, believe me, and here's why. Let's imagine for a minute that a new species of organism evolved today, one with a really exotic metabolism -- one that, where you and I take in oxygen and release carbon dioxide, took in our familiar air and released hydrogen fluoride. As the article behind that link describes, hydrogen fluoride is truly vicious stuff -- it's violently corrosive and extremely toxic, the kind of acid that dissolves glass outright and kills you with acute fluoride poisoning if the horrid chemical burns don't do it first.
Now imagine that this organism succeeded. Really succeeded. It spread all over the planet. Its breath corroded the very ground it lived on, and now there was a lot of it -- enough to burn off the entire surface of the earth. It wouldn't stop when the soil was seared away and the rocks saturated with fluoride, either: those things would still be alive, and still spitting their poison, only now it'd be building up in the air. In a geological eyeblink, they'd choke the entire atmosphere with toxic acid. I'm not going to describe exactly what would happen to life on Earth in that situation, but you can probably fill in the blanks yourself.
That's what happened when photosynthesis first arose.
When the earth was young, and life was just getting started, there was virtually no oxygen in Earth's atmosphere. Free O2 is reactive stuff; it had all gotten bound up in carbon dioxide. The atmosphere of the time was mostly nitrogen and CO2. Early life on Earth had evolved to be comfortable in that environment; to those early species, oxygen was a corrosive metabolic poison -- much like, say, hydrogen fluoride is to us.
Then, about 2.5 billion years ago, the first photosynthetic organisms evolved. They were something like cyanobacteria -- blue-green algae -- and probably not very efficient by modern standards, but they succeeded, and they started cranking out oxygen by the ton. At first it just corroded the rocks, oxidizing them quickly and thoroughly; those first blue-green algae literally rusted the entire planet, and when the rocks were saturated, they started poisoning the atmosphere.
We have no way of knowing what the death toll was like, as free oxygen built up towards the modern 20% or so -- hard skeletons hadn't evolved yet, so nothing much from that era ever fossilized -- but it was assuredly unimaginable. This Oxygen Catastrophe was the first of Earth's great mass extinctions, and it made the slaughter of the dinosaurs look like barely a blip.
Mercifully, it never happened again. The few species that survived the Oxygen Catastrophe learned to work with free oxygen; aerobic respiration actually turned out to be pretty effective. The staggering diversity of life today is all descended from those survivors.
...Well, it never happened again, until very, very recently. Just an evolutionary eyeblink ago, another species with the ability to transform its whole world's atmosphere arose. It spread across the globe. It started cranking out its chosen gases in geologically-significant quantities. Just now, some individuals have even begun to notice what their species is doing. Some of them are taking steps toward making it stop.
Makes you think twice about how scary climate change might be, doesn't it?
Friday, August 10, 2012
Wednesday, June 6, 2012
Glasswort by any other name: Salicornia
Yesterday we saw the most obvious way for a plant to deal with excess salt -- by taking it up and then immediately getting rid of it. That strategy works, as the dunegrasses' success can attest, but there's more than one way to peel an orange. Today, let's have a look at Salicornia, a genus with a lot of names (glasswort, pickleweed, sea pickle, marsh samphire, pousse-pierre...) and one interesting way of dealing with salt.
Salicornia plants are odd-looking little things, though you might have to get close to see very much; most species don't get much larger than a foot tall. With their thick, succulent stems and tiny, scale-like leaves pulled in close, they look mostly leafless, and indeed the stems do most of their photosynthesis. Some species are edible, sold as a delicacy under the names "sea beans" or "samphire greens"; it's also been used in the glass industry, as a source of soda ash. These two uses, as a salty food and as a source of sodium carbonate, betray one important fact: mature Salicornia plants are chock full of salt. Yes, it's the same salt you're thinking -- sea salt, table salt, salt that sucks the water right out of living things.
How do they manage it without dying of dehydration? Glassworts, it turns out, have a special modification to their cells' vacuoles. Virtually every plant cell has a vacuole; it's essentially just a large membrane-bound bubble in the middle of the cell, which the cell uses to store water, control its size, and dump substances it doesn't want. For Salicornia, those substances include salt. It can keep salt locked up in the vacuole even when the concentrations inside are many times that of the rest of the cell, high enough that most plants couldn't keep the stuff contained and would die of dehydration. For these tough little oddballs, it isn't a problem; they just go on doing their thing with bubbles of saline death locked down right in the middle of every cell.
Hence their names: pickleweed for the salty flavor, sea pickle for the tolerance to ocean salinity, glasswort for being so rich in salt that the glass industry once used them as sodium collectors.
Image source: Folini, Franco. American Glasswort (Salicornia virginica) (6122382261). Retrieved 6 Oct 2014, from Wikimedia Commons: <http://commons.wikimedia.org/wiki/File:American_Glasswort_(Salicornia_virginica)_(6122382261).jpg>
_(6122382261).jpg/450px-American_Glasswort_(Salicornia_virginica)_(6122382261).jpg) |
| Salicornia virginica in flower. The blossoms are those tiny stringlike structures at the ends of the branches. |
Salicornia plants are odd-looking little things, though you might have to get close to see very much; most species don't get much larger than a foot tall. With their thick, succulent stems and tiny, scale-like leaves pulled in close, they look mostly leafless, and indeed the stems do most of their photosynthesis. Some species are edible, sold as a delicacy under the names "sea beans" or "samphire greens"; it's also been used in the glass industry, as a source of soda ash. These two uses, as a salty food and as a source of sodium carbonate, betray one important fact: mature Salicornia plants are chock full of salt. Yes, it's the same salt you're thinking -- sea salt, table salt, salt that sucks the water right out of living things.
Hence their names: pickleweed for the salty flavor, sea pickle for the tolerance to ocean salinity, glasswort for being so rich in salt that the glass industry once used them as sodium collectors.
Image source: Folini, Franco. American Glasswort (Salicornia virginica) (6122382261). Retrieved 6 Oct 2014, from Wikimedia Commons: <http://commons.wikimedia.org/wiki/File:American_Glasswort_(Salicornia_virginica)_(6122382261).jpg>
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Tuesday, June 5, 2012
A sparkling coat of death: saltwater cordgrass
Word-association time! Answer this question with the first thing that comes into your head: What does one do with watermelon seeds?
If you're like me, or like millions of other Americans who grew up where melons could be had, you probably answered something like "spit them". When we eat watermelons1, we eat a big bite of delicious fruit and are left with the inedible seeds. Those, we spit out. (If you're a kid and it's a lazy summer afternoon, you have contests to see who can spit them the farthest.) We've taken in the part that nourishes us (yum, watermelon!) and gotten rid of the part we don't need (ptui, seeds).
Now what if the seeds were poison, and watermelon were the only thing we had to eat? We'd be like saltwater cordgrass (Spartina alterniflora). Native to the east coast of the USA, this plant grows in coastal sand dunes, where the only water available to it is thick with salt. In a habitat like that, most grasses quickly shrivel, drinking deep of seawater and still dying of dehydration. Spartina, though, thrives.
How does it manage? Like a person eating a slice of watermelon and spitting out the seeds, Spartina takes in seawater and actually spits out the salt. Specialized glands on its leaves exert a force stronger than osmosis, drawing the salt out of the water it sups, and excrete it onto the leaf surface in crystalline form. Until the rain washes them away, these crystals sit on the leaves and sparkle, visible to the naked eye.
Image source: Field Studies Council. "Spartina." Retrieved 10 Aug 2012 from <http://www.theseashore.org.uk/theseashore/Saltmarsh%20section/species/Spartina.html>
1. The older cultivars, not the new "seedless" ones.
If you're like me, or like millions of other Americans who grew up where melons could be had, you probably answered something like "spit them". When we eat watermelons1, we eat a big bite of delicious fruit and are left with the inedible seeds. Those, we spit out. (If you're a kid and it's a lazy summer afternoon, you have contests to see who can spit them the farthest.) We've taken in the part that nourishes us (yum, watermelon!) and gotten rid of the part we don't need (ptui, seeds).
Now what if the seeds were poison, and watermelon were the only thing we had to eat? We'd be like saltwater cordgrass (Spartina alterniflora). Native to the east coast of the USA, this plant grows in coastal sand dunes, where the only water available to it is thick with salt. In a habitat like that, most grasses quickly shrivel, drinking deep of seawater and still dying of dehydration. Spartina, though, thrives.
 |
| Spartina leaves. See the clumps of salt? |
Image source: Field Studies Council. "Spartina." Retrieved 10 Aug 2012 from <http://www.theseashore.org.uk/theseashore/Saltmarsh%20section/species/Spartina.html>
1. The older cultivars, not the new "seedless" ones.
Monday, June 4, 2012
Salt Lovers' Week: meet the halophytes
Water, water everywhere, nor any drop to drink... Coleridge knew it, sailors have always known it, and anyone who's been to the beach certainly knows it: salt water is no drop to drink. Water with as much salt as is found in seawater can, in fact, be lethal. It literally dehydrates the drinker,1 making you thirstier even as you guzzle it down. Humans can't survive on salt water.
1. By osmosis. If you have two aqueous solutions (things-dissolved-in-water) side-by-side, the water will tend to move from the less-concentrated to the more-concentrated one. The liquid in your tissues has less stuff dissolved in it than seawater does, so the salt water literally sucks the water out of your body. Nasty.
Neither can plants, and for much the same reasons. Salt water dehydrates them just as it dehydrates us, sucking the moisture out of their tissues and leaving them to wilt and die. There's a reason that ancient armies would salt an enemy's farmland if they wanted to destroy it utterly: salted ground can't support crops. Not even barnyard weeds will grow in land seeded with salt.
Like virtually everything in biology, though, this prohibition isn't absolute. Salty ground is harsh and unforgiving, but many species of plants -- halophytes -- have grown to live in it anyway. Dunegrasses take up the salt, then spit it right back out. Glasswort takes it up, puts it aside, and lives with it anyway. Tamarisks can tolerate salt well enough to take over the salt-crusted desert waterholes of the American West. Some plants can even live fully immersed in extremely salty water -- they must have managed it, if they were to survive the primordial oceans.
This week, look for a post each day, each dealing with one of these extraordinary plants as it thumbs its nose at the killing salts.
1. By osmosis. If you have two aqueous solutions (things-dissolved-in-water) side-by-side, the water will tend to move from the less-concentrated to the more-concentrated one. The liquid in your tissues has less stuff dissolved in it than seawater does, so the salt water literally sucks the water out of your body. Nasty.
Friday, May 4, 2012
Wednesday, May 2, 2012
What we call "a flower" isn't always just a flower. Often, it's actually a mass of several, tens, or even hundreds of tiny flowers -- an inflorescence -- condensed until it looks like one unit, sometimes with extra "petals" formed from tissues that aren't flowers at all. Jack-in-the-pulpit, dandelions and daisies, and poinsettias are all good examples of this particular weirdness.
Friday, April 27, 2012
Plants get sunburn, too, and it's bad for them for a lot of the same reasons that it's bad for us: it damages their DNA, frequently killing cells outright. To fight sunburn, they actually make natural sunscreens -- chemicals called flavonoids, which are transparent to visible light but opaque to dangerous UV.
Wednesday, April 25, 2012
Tuesday, April 24, 2012
Announcement: a new format
First off, I'd like to apologize for the Daily Cypsela's recent unannounced hiatus. It seems that a full-length post every day, on top of a full-time job and assorted other responsibilities, hobbies, etc., is more than I can really handle. As such, the Cypsela will, from now on, no longer be truly Daily. I really am sorry about that.
That does not, however, mean that this blog is to be abandoned. A full-length post every day may be too much, but a full-length one once or twice a week is completely manageable. Also, I plan to fill some of the gaps with entries even more like cypselae than the longer posts: little fun-fact sound bites, things that will fit into Facebook statuses or even tweets. Some of these mini-posts (tagged "cypsela") will be teasers for later full-length posts, in which I'll elaborate on some botanical wonder that the earlier blurb just pointed to.
We'll see how well the new schedule works out. Comments are, as always, very welcome.
And now, back to our semi-regularly-scheduled programming...
That does not, however, mean that this blog is to be abandoned. A full-length post every day may be too much, but a full-length one once or twice a week is completely manageable. Also, I plan to fill some of the gaps with entries even more like cypselae than the longer posts: little fun-fact sound bites, things that will fit into Facebook statuses or even tweets. Some of these mini-posts (tagged "cypsela") will be teasers for later full-length posts, in which I'll elaborate on some botanical wonder that the earlier blurb just pointed to.
We'll see how well the new schedule works out. Comments are, as always, very welcome.
And now, back to our semi-regularly-scheduled programming...
Wednesday, April 18, 2012
Hair-triggered suction traps: the bladderworts
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| A clump of Utricularia vulgaris in flower. Innocuous, right? |
Below the water, and at a much smaller scale, is where things get interesting. Look closely at those fine feathery leaves. Find the little rounded bladders that cling to them all over. Those aren't some kind of parasite -- they're part of the plant. In fact, they're its means of trapping prey.
The bladders, when they first develop, have a near vacuum inside. Their trap-door openings stay firmly shut, maintaining that suction-cup strain. Just outside the door, poking into the water like delicate whiskers, are one or more tiny hairs. Those hairs are fine triggers, poised, connected to the door.
When a water flea or tiny insect larva trundles by, brushing against those hairs -- snap! The trap door pops open, sucking water into the bladder, and the prey is swept along with it. The door snaps shut a fraction of a second later. By now, you can probably predict the end result: digestive enzymes, liquid bug, and the plant gets a very necessary dinner. Without the traps, the plant's growth slows dramatically, as it can't get enough nutrition from the acidic, nutrient-poor water of its native bogs.
Bladderwort traps are powerful things, especially for their size. If the plant is removed from the water (say, by a curious human), it often comes out with a spatter of audible crack! sounds: its traps springing shut on empty air.
Image source: Hillewaert, Hans. Utricularia vulgaris. Retrieved 17 Apr 2012, from Wikimedia Commons: <http://commons.wikimedia.org/wiki/File:Utricularia_vulgaris.jpg>
Tuesday, April 17, 2012
Sparkly but lethal: the sundews
The sundews, Drosera spp., set a wholly different sort of booby-trap for their prey. They do not move to trap it, not as dramatically as Venus flytraps do, but like Venus flytraps they depend on the hapless insect landing directly on their leaves.
Those leaves are beautiful, to the unwary: they sparkle in the light, giving the genus its common name. Those drops of liquid on their little stalks aren't just dew, though. For one thing, they're nectar-like, full of tasty sugar. Any hapless insect that lands to sip the bounty, though, will find out something else about them: they're sticky.
A bug tricked into landing on a sundew leaf is quickly and effectively glued down, unable to free itself. Even if it only brushed one sticky droplet, the stalks bearing other droplets -- appropriately known as tentacles -- move towards it, glomming many other droplets onto its body. Some sundews can snap these tentacles into place in fractions of a second, faster than any prey can respond.
The prey's futile struggles inevitably kill it, either through exhaustion or through suffocation as the sticky lures clog its breathing. Slowly, then, the tentacles begin to tug on its body. The leaf curls inward around its trapped insect, and the glands that secreted the sugary lure start to secrete digestive enzymes. The prey is reduced to a nutrient soup, which the plant absorbs through other glands on the leaf surface. Dinnertime for the sundew.
Like all carnivores, though, these plants aren't being vicious. Drosera roots are effectively useless for nutrient uptake: without the nutrients they capture from their prey, they would sicken and die very quickly. It's all perfectly natural -- beautiful, even, in the fierce and sharp-edged way that nature so often is.
Image source: Elhardt, Noah. Drosera capensis bend. Retrieved April 16, 2012, from Wikimedia Commons: <http://commons.wikimedia.org/wiki/File:Drosera_capensis_bend.JPG>
Those leaves are beautiful, to the unwary: they sparkle in the light, giving the genus its common name. Those drops of liquid on their little stalks aren't just dew, though. For one thing, they're nectar-like, full of tasty sugar. Any hapless insect that lands to sip the bounty, though, will find out something else about them: they're sticky.
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| A Drosera capensis leaf bending to surround and digest a trapped fly. Normally the leaves are more or less straight. |
The prey's futile struggles inevitably kill it, either through exhaustion or through suffocation as the sticky lures clog its breathing. Slowly, then, the tentacles begin to tug on its body. The leaf curls inward around its trapped insect, and the glands that secreted the sugary lure start to secrete digestive enzymes. The prey is reduced to a nutrient soup, which the plant absorbs through other glands on the leaf surface. Dinnertime for the sundew.
Like all carnivores, though, these plants aren't being vicious. Drosera roots are effectively useless for nutrient uptake: without the nutrients they capture from their prey, they would sicken and die very quickly. It's all perfectly natural -- beautiful, even, in the fierce and sharp-edged way that nature so often is.
Image source: Elhardt, Noah. Drosera capensis bend. Retrieved April 16, 2012, from Wikimedia Commons: <http://commons.wikimedia.org/wiki/File:Drosera_capensis_bend.JPG>
Monday, April 16, 2012
Don't fall in: the pitcher plants
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| Nepenthes edwardsiana pitcher. Steer clear, if you're a bug. |
Pitcher plants belong to five different genera in three different orders1, completely unrelated to each other, which is always a sign that something about them is adaptive (it works well enough to be "invented" independently). All of them share a common means of catching their little flying vitamin pills. They grow modified urn-shaped leaves -- "pitchers" -- with downward-pointing hairs or intricate grooves on their inner walls and a few milliliters of liquid in the bottom. The pitchers look or smell somehow enticing to their prey (some Nepenthes even produce sweet nectar as a lure), but the lure is just that: bait.
An insect that blunders into a pitcher plant's pitcher is usually doomed, as pitchers are very effective traps. Their walls are slippery and often grooved or covered with downward-pointing hairs, so that trying to climb out is like trying to force your way through a vertical hedge to climb a wall of slick ice. The trapped insect is forced into the pool of liquid at the bottom, where it eventually drowns.
Drowning isn't the end, though, because that liquid isn't just water. It's a solution of acid and digestive enzymes, much like the contents of a (much-diluted) human stomach. A drowned bug will be dissolved and digested over a period of days or weeks. The plant will absorb its nutrients through the walls of the pitcher, and hey presto! Dinner!
Contrary to popular belief, by the way, there is no such thing as a pitcher plant large enough to eat a human. The largest carnivorous plants in the world are pitcher plants -- Nepenthes rajah is the current champion -- but even they can't manage anything bigger than a small lizard or songbird.
Image source: Robinson, Alastair. Nepenthes edwardsiana entire ASR 052007 tambu. Retrieved April 16, 2012, from Wikimedia Commons: <http://en.wikipedia.org/wiki/File:Nepenthes_edwardsiana_entire_ASR_052007_tambu.jpg>
1. Nepenthes in the Caryophyllales; Heliamphora, Sarracenia, and Darlingtonia in the Ericales; and Cephalotus in the Oxalidales, in case anyone was wondering.
Monday, February 13, 2012
It's a leaf! It's a root! It's a... wait, what?
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| Tmesipteris elongata at Otira, New Zealand. Looks pretty normal, right? |
Sometimes, though, diversity isn't exactly what is needed, and plants simplify instead. Tmesipteris is a genus of unusual, "primitive" ferns, found only in a few scattered places in the South Pacific. To a casual eye, it looks as though it has all the usual parts of a fern -- roots, stems, leaves, and even the sort of spore capsules you'd expect on such an ancient lineage. It takes a much closer look, by which I mean microscopes and developmental analysis, to realize that something is odd there.
Those broad green structures along its stem, the ones that do most of its photosynthesizing? They're not leaves. The thready bits at its base, the ones that attach it to the bark where it lives? They're not roots.
Every single part of a Tmesipteris plant is, if you look closely enough, a modified stem.
At some point in the evolutionary past, this plant's ancestors found that leaves, roots, the whole shebang, were all -- for whatever reason -- unnecessary. As I pointed out before, evolution ditches unnecessary things pretty quickly. Why bother with leaves when you can just grow flat bits of stem, and they'll photosynthesize just fine? Why bother with roots when you can just grow thready stem-anchors, and they'll keep you nailed down just as well as you need? Other plants have found plenty of reasons to bother, but for Tmesipteris, there just wasn't a need. It's gotten along very well this way for something like 400 million years, thankyouverymuch, and it has no reason to change now.
Image source: Liefting, Alan [Public domain]. Tmesipteris elongata. Retrieved February 12, 2012, from Wikimedia Commons: <http://commons.wikimedia.org/wiki/File:Tmesipteris_elongata.jpg>
Wednesday, February 8, 2012
The elements of life
Plants are, in large part, literally defined by photosynthesis. It's practically alchemical, that ability to live on just air and water and sunshine. Yes, we know precisely how the process works -- it's a complex chain of chemical reactions whose details I won't discuss here -- but that doesn't remove the wonder. Photosynthesis produces the sugars that fuel a plant's metabolism and make up the building blocks of its structure. It is the source of well over 90% of a plant's mass.
Now consider this: that mass is mostly pulled out of thin air.
Let me explain, and bear with me for a minute. Photosynthesis, to make it simple, takes water from the soil and carbon dioxide from the air, then uses energy from light to pull an oxygen out of them and rearrange their remaining atoms into sugar. The overall chemical equation looks like this:
6CO2 + 6H2O + energy --> C6H12O6 + 6O2
Six molecules of carbon dioxide plus six of water plus energy are rearranged to give one molecule of glucose -- sugar -- and six of oxygen. There are quite a lot of intermediate steps, but this is what you get when you look only at what goes in (CO2, water, sun) and what comes out (sugar, oxygen).
The really fascinating thing, when you think about it, is where each of those atoms comes from and where it goes. All the carbon and oxygen atoms in the sugar come from CO2: the ones from water are thrown away as oxygen. Water only contributes hydrogen, which is important but not very heavy -- about 4% of the sugar's mass. Sunlight is absolutely crucial to the process, but it contributes energy, not matter. In the end, fully 96% of the sugar's mass comes from carbon dioxide.
That's what I mean when I say that most of a plant is made of thin air. Nearly 96% of its mass comes from just that. The rest comes from water, plus a fraction of a percent from trace minerals in the soil. Air, water, and soil, all of it held together with sunlight: it's the stuff of life.
That's not just true of plants, either. In virtually every biome on Earth, plants form the bottom of the food chain. The sugars they make provide energy for them, and for the herbivores that eat them, and for the carnivores that eat the herbivores, and so on. Almost every living thing is ultimately made of plant matter. We are made of plant matter: everything humans eat can be traced back to a plant.
When you get right down to it, then, all life on Earth is made of very simple things. We are air and water and a little bit of soil, all held together with sunlight.
Now consider this: that mass is mostly pulled out of thin air.
Let me explain, and bear with me for a minute. Photosynthesis, to make it simple, takes water from the soil and carbon dioxide from the air, then uses energy from light to pull an oxygen out of them and rearrange their remaining atoms into sugar. The overall chemical equation looks like this:
6CO2 + 6H2O + energy --> C6H12O6 + 6O2
Six molecules of carbon dioxide plus six of water plus energy are rearranged to give one molecule of glucose -- sugar -- and six of oxygen. There are quite a lot of intermediate steps, but this is what you get when you look only at what goes in (CO2, water, sun) and what comes out (sugar, oxygen).
The really fascinating thing, when you think about it, is where each of those atoms comes from and where it goes. All the carbon and oxygen atoms in the sugar come from CO2: the ones from water are thrown away as oxygen. Water only contributes hydrogen, which is important but not very heavy -- about 4% of the sugar's mass. Sunlight is absolutely crucial to the process, but it contributes energy, not matter. In the end, fully 96% of the sugar's mass comes from carbon dioxide.
That's what I mean when I say that most of a plant is made of thin air. Nearly 96% of its mass comes from just that. The rest comes from water, plus a fraction of a percent from trace minerals in the soil. Air, water, and soil, all of it held together with sunlight: it's the stuff of life.
That's not just true of plants, either. In virtually every biome on Earth, plants form the bottom of the food chain. The sugars they make provide energy for them, and for the herbivores that eat them, and for the carnivores that eat the herbivores, and so on. Almost every living thing is ultimately made of plant matter. We are made of plant matter: everything humans eat can be traced back to a plant.
When you get right down to it, then, all life on Earth is made of very simple things. We are air and water and a little bit of soil, all held together with sunlight.
Tuesday, January 31, 2012
A literal hair-trigger: Venus flytraps
The Venus flytrap, Dionaea muscipula, is probably the most famous of carnivorous plants, and for good reason. The spike-toothed traps that snap closed fast enough to capture fast-flying insects are unique among plants. Not only do they move quickly -- they're among the fastest things in the plant kingdom -- they do so only at a very, very precise trigger.
When an insect lands on the flytrap's trap (actually a modified leaf), it brushes against tiny hairs on the leaf surface. Touching those hairs triggers the trap, and it snaps shut. At first, there's still a little gap between the "teeth" of the trap, though, which lets very small prey escape -- that way, the plant doesn't have to waste its energy digesting something too small to be of any use. When too small a bug triggers the trap and then escapes, the trap can open back up within 12 hours. There's no need to waste time and digestive juices on a useless gnat.
If the trapped bug is big enough, though, it won't be able to slip out. Instead, it'll just keep squirming inside the trap: the continued pressure on the hairs tells the plant to seal the trap completely, pushing its edges together until it's a watertight pocket. Once that has happened, the plant releases digestive juices into the pocket. These juices break down and dissolve all the soft parts of the bug so that the plant can absorb the nutrients in it. Once this is finished, about 10 days later, the bug is nothing but an empty exoskeleton. The trap then opens back up, letting the bug-husk fall away and getting ready for its next meal.
When an insect lands on the flytrap's trap (actually a modified leaf), it brushes against tiny hairs on the leaf surface. Touching those hairs triggers the trap, and it snaps shut. At first, there's still a little gap between the "teeth" of the trap, though, which lets very small prey escape -- that way, the plant doesn't have to waste its energy digesting something too small to be of any use. When too small a bug triggers the trap and then escapes, the trap can open back up within 12 hours. There's no need to waste time and digestive juices on a useless gnat.
If the trapped bug is big enough, though, it won't be able to slip out. Instead, it'll just keep squirming inside the trap: the continued pressure on the hairs tells the plant to seal the trap completely, pushing its edges together until it's a watertight pocket. Once that has happened, the plant releases digestive juices into the pocket. These juices break down and dissolve all the soft parts of the bug so that the plant can absorb the nutrients in it. Once this is finished, about 10 days later, the bug is nothing but an empty exoskeleton. The trap then opens back up, letting the bug-husk fall away and getting ready for its next meal.
Monday, January 30, 2012
Carnivory Week: When plants get hungry
Everyone knows that carnivorous plants exist. Even if their sheer weirdness and amazing capabilities hadn't already brought them into classrooms, Little Shop of Horrors would have cemented them firmly in the popular consciousness. One thing that's rarely discussed, though, is exactly why a plant would resort to carnivory. Why bother catching and eating animals when you're a plant and can already make all your own food?
The answer is simple: minerals. Carnivorous plants are as good at photosynthesis as any other species, but photosynthesis only makes sugar. They still need soil nutrients -- nitrogen, phosphorus, potassium, and a host of other trace minerals -- for the same reason that people need our vitamins. Most plants get their nutrients from the soil, where the stuff is abundant; farmers and gardeners add minerals, in the form of fertilizer, to help their crops thrive.
On its own, though, a plant can't very well pop down to Home Depot and buy itself a bag of fertilizer. When the soil lacks important minerals, what's a plant to do? Some species have found ways to conserve or reuse scarce nutrients, making a little go a long way. Others have found ways of making their own: legumes can pull nitrogen right out of the air (and that's a subject for another post). Carnivorous plants do neither. Instead, they just let their prey bring the goods right to them.
When a plant traps and digests, say, a fly, it gets to suck up all the nutrients in that bug's body. There's nitrogen in the protein of its muscles, potassium in its nerves to let them fire, phosphorus down the very backbone of its DNA, and much more. A single fly can save the plant from a startling amount of malnutrition. Carnivorous plants aren't just being vicious: like any carnivore, they're only trying to survive.
This week, look for posts on the wonders of four different carnivorous plants: the literal hair-triggers of the Venus flytrap, the booby traps set by pitcher plants, the gluey hairs on sundews, and the vacuum suction of the bladderwort.
The answer is simple: minerals. Carnivorous plants are as good at photosynthesis as any other species, but photosynthesis only makes sugar. They still need soil nutrients -- nitrogen, phosphorus, potassium, and a host of other trace minerals -- for the same reason that people need our vitamins. Most plants get their nutrients from the soil, where the stuff is abundant; farmers and gardeners add minerals, in the form of fertilizer, to help their crops thrive.
On its own, though, a plant can't very well pop down to Home Depot and buy itself a bag of fertilizer. When the soil lacks important minerals, what's a plant to do? Some species have found ways to conserve or reuse scarce nutrients, making a little go a long way. Others have found ways of making their own: legumes can pull nitrogen right out of the air (and that's a subject for another post). Carnivorous plants do neither. Instead, they just let their prey bring the goods right to them.
When a plant traps and digests, say, a fly, it gets to suck up all the nutrients in that bug's body. There's nitrogen in the protein of its muscles, potassium in its nerves to let them fire, phosphorus down the very backbone of its DNA, and much more. A single fly can save the plant from a startling amount of malnutrition. Carnivorous plants aren't just being vicious: like any carnivore, they're only trying to survive.
This week, look for posts on the wonders of four different carnivorous plants: the literal hair-triggers of the Venus flytrap, the booby traps set by pitcher plants, the gluey hairs on sundews, and the vacuum suction of the bladderwort.
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