Friday, July 4, 2008

What's it for?

Amorphophallus titanum, immature inflorescence, with a leaf from a young plant of the same species emerging at right.

I've been giving greenhouse tours to all sorts of groups for quite a few years now, and on more than one occasion--usually prompted by some plant that is completely outside of normal experience, like the Corpse Flower pictured here--a student or garden club member has asked, in these exact words: "But, what's it for?" That's a fairly open ended metaphysical question, but I think that the answer that people are looking for is something practical and immediate, like: "Local people in Sumatra use the leaves for umbrellas." Of course, it isn't really true that anyone uses Amorphophallus titanum to keep out of the rain, as far as I know.

In the absence of known utility for humans, I imagine that it would still be reasonably satisfying for the questioner to hear that, say, elephants eat the leaves, or at least that pretty butterflies visit the flowers. But again, I don't think that anything like that is true of A. titanum: as with other members of the genus, the leaves of the Corpse Flower are probably loaded with calcium oxalate crystals and other toxins. The flowers, famously, broadcast a putrid stench that does not attract charismatic pollinators like butterflies. Even the carrion insects that are drawn by the smell of decay are hapless dupes who receive no obvious benefit from their visit: the blooms merely produce a rotten smell, and yield nothing that a carrion beetle or sweat bee could actually lay eggs in or eat.

It's a safe bet that innumerable bacteria, fungi, mites, nematodes and other tiny organisms do live in association with a Corpse Flower growing in the rain forest. But a tour group is--rightly--not going to be satisfied by: "Well, if it's like other plants that have been studied, there are microbes that live around the roots, feeding on secretions of the root cap. But nobody has ever studied the rhizosphere flora of this species, and probably nobody ever will, unless evidence turns up that something unusual is going on with it. Which it probably won't. Evidence, that is. So yeah, errr, I guess, um, nobody knows for sure." The cute way to answer the "what's it for?" question would be to say "It brings in paying visitors and increases web traffic!" But even if there were an appealing, straightforward, practical purpose for the Corpse Flower (the tubers of related species are edible when suitably processed, for example, and there's no reason to expect that A. titanum would be any different, if it could be cultivated on a large scale), such an answer would be superficial at best, and probably a bit of a dodge, too.

There is a much deeper answer to the question of what the Corpse Flower is for, an answer that yields real insights and productive, testable ideas about why the plant has such peculiar characteristics. It's the answer that Darwin and Wallace gave to the world 150 years ago, almost to the day, for living things in general, not just A. titanum. It's just not tremendously satisfying to the average greenhouse tour-goer. For that matter, because of the workings of human psychology, it probably doesn't have much in the way of purely visceral appeal as an explanation to anyone, even the scientists who have formulated it. But whatever the answer lacks in terms of surface emotional satisfaction, it more than makes up for in pure utility for those who have studied the questions. Because, as far as anyone can tell, Darwin's answer is correct.

The metabolic processes that synthesize the chemicals that give A. titanum blooms their foul odor, the metabolic short circuit that generates the heat to volatilize those chemicals, the tall but thriftily constructed spadix from which the odor wafts into the sultry night air; these and a million other characteristics are what allowed the ancestors of the plant in the University greenhouse to germinate, to grow, to out-compete other plants, to resist herbivores and disease, to exchange pollen, to set and disperse seed. These adaptations permitted the ancestors of our A. titanum, now marooned in Connecticut, to survive and reproduce, century after century, in a teeming rain forest where the competition and the environment were always changing, slowly but inexorably.

What's the Corpse Flower for? It is for making more Corpse Flowers.


Patty H said...

Fantastic ruminations on the Titan Arum Matt. A wonderfully humorous commentary that I will no doubt share as a docent as our own Titan unfolds in the next couple of weeks at the Volunteer Park Conservatory in Seattle. Thanks for a fun read.

Matt said...

Thanks Patty, and I hope your Titan brings lots of attention to your conservatory!