A botanical chameleon

A plant that mimics its neighbors... and we still don't know how it works

One of the things I love most about science is its capacity to astonish us.

You can be really knowledgeable in a field, and then the natural world slings a curve ball at you and leaves you amazed. Sometimes these unexpected twists trigger profound leaps in our understanding—an example is the discovery of the parallel magnetic stripes in igneous rocks along the Mid-Atlantic Ridge leading to the theory of plate tectonics—but sometimes it’s just a fascinating bit of scientific trivia, one of those little things that makes you smile in a bemused sort of way and say, “Science is so cool.”

I had a moment like that recently. I taught biology for 32 years and have been interested in plants—especially tropical plants—a great deal longer than that. I have a fine collection of tropicals, that during our frigid winters are jammed into my greenhouse so tightly that I can barely walk through it. Now that it’s warm (freakin’ hot, actually), most of them are in their summer homes on my deck and patio, enjoying the high temperatures probably a great deal more than I am. I have bromeliads, cacti, three species of ginger, two different kinds of angel’s trumpet (one of which got to be seven feet tall last summer, and sometimes had twenty giant, peach-colored flowers all blooming at once), two fig trees that produce every year, and two species of eucalyptus.

Among others.

While I wouldn’t call myself an expert when it comes to tropical plants, I’m at least Better Than The Average Bear. So I was startled to run, quite by accident, into an account of a species I had never even heard of—and even more startled when I found out how truly bizarre and unique this plant is.

It’s called the “chameleon vine,” and its scientific name is Boquila trifoliolata. It belongs to a small and rather obscure family of dicots called Lardizabalaceae, which contains forty species found in two places—southeast Asia and western South America. (How a group of plants with common ancestry ended up in such widely separated locales is a mystery in and of itself; populations like this are called peripheral isolates and are a perennial puzzle in evolutionary biology.)

Boquila is one of the South American ones, and lives in southern Chile and Argentina. It’s a woody vine whose leaves are composed of three leaflets (thus the plant’s species name). Here’s a picture:

[Image licensed under the Creative Commons Inao, Boquila trifoliata [sic], CC BY-SA 2.0]

It’s not really much to look at, and you non-botanical types are probably tapping your fingers and saying, “So what?” But wait till you hear what this plant can do—and why it merits its common name of “chameleon vine.”

Boquila trifoliolata has an extraordinary ability called mimetic polymorphism. It’s capable of altering its leaf shape to mimic a variety of different (unrelated) plants—including the ones it most commonly twines up as a support. We’re not talking about small differences, either. It can be glossy or dull, have different petiole lengths, have different leaflet sizes and shapes, and even change whether or not it has serrations or spines along the edge!

This ability, first described in a paper by botanists Ernesto Gianoli and Fernando Carrasco-Urra in Current Biology in 2014, was first attributed to genetic transfer from the host to the vine, a sort of genetic parasitism. I’ll admit that was the first explanation I thought of—although how a plant could take up DNA from another species and only express the genes related to leaf morphology left me scratching my head a little. But Gianoli and Carrasco-Urra were able to rule out this possibility, because Boquila can alter its leaf shape without touching the plant it’s mimicking.

All it has to do is be nearby. So it isn’t a parasite at all. The current guess is that Boquila is picking up volatile organic compounds emitted by the other plant, and those are altering gene expression, but the alleged organic compounds have yet to be identified—nor has any kind of specific mechanism by which that kind of alteration in phenotype could happen.

Even though we still have no idea how Boquila is managing this neat trick, the why is pretty clear. If it’s hiding amongst the foliage of another plant, herbivores can’t single it out for a snack. Gianoli and Carrasco-Urra found that when Boquila is climbing up a non-living support like a chain-link fence, herbivores actually seek it out for browsing. But when it’s camouflaged within another plant’s leaves, it can avoid being seen and identified—and, they found, browsing of its foliage dropped by as much as fifty percent.

Fascinating, isn’t it? And yet despite study, we haven’t been able to figure out how the plant evolved this amazing (and apparently unique in the plant world) ability, nor what kind of information it’s gleaning that might say, “Okay, time to change color and grow some spikes!”

So yet another example of how science is really freakin’ cool. It also illustrates how every new discovery opens up new avenues for investigation. The crazy chameleon plant should make it absolutely clear that if you go into science, you’ll never be done learning.