The many faces of poison ivy

July 10, 2006 2:39 PM

Being in the midst of my first bout of urishiol-induced contact dermatitis, I'm using some of my downtime to read up on the culprit: Poison Ivy. Along the way, however, I've come across some confusing information...

According to the Wikipedia article and several other sources, the plant itself can grow in several modes: as a free-standing shrub, as ground cover, and as a climbing vine.

Being a rural boy myself, I'd been familiar with different modes of growth in Blackberries, but always attributed these different modes (free-standing shrub & ground cover vine) to genetic variation - variation in the appearance and quality of their respective product seemed to support this theory.

The absence of listed poison ivy subspecies suggests that this theory is not applicable to that plant, and indeed may have been an incorrect assumption on my part with blackberries.

Can any amateur or professional botanists out there advise as to whether (and how) genetically identical plants can "choose" different modes of growth to conform to their present environment?

posted by The Confessor to science & nature (7 comments total)

Though IANAB, I suspect the variations are a result of local environment. That and, perhaps, a certain genetic adaptability to said different environments. Growing next to a vertical structure or tree? Climb up. Out in the open? Shrub. Lots of low-lying growth? Go ground cover.
Just a hunch, mind you. I battle poison ivy all summer around my house and can can attest to its adaptability.
posted by Thorzdad at 3:00 PM on July 10, 2006

Phenotypic Plasticity
posted by mcstayinskool at 3:05 PM on July 10, 2006

Fascinating, mcstayinskool!

I'd never heard of that concept applied beyond the insect world, and my understanding of it was incomplete even there!

Do you know of any highly variant plant for which exhaustive behavioral studies have been done? Given its noxious nature, poison ivy would appear to be a poor candidate...
posted by The Confessor at 4:31 PM on July 10, 2006

I know of one case which isn't a plant. There's a salamandar called the Axolotl which has a juvenile form (with gills) and an adult form (with lungs).

Ordinarily, however, they don't lose their gills. They stay aquatic and breed in that form. But if there's a dry period, they develop their lungs and the gills will wither.
posted by Steven C. Den Beste at 4:52 PM on July 10, 2006

I once had a terrible case of poison ivy, too, and used the time to learn all about plants and indoor gardening.

I'm pretty sure it's only adaptable due to environment. English Ivy acts the same way, pretty much. The vine puts out "air roots" that will react differently to surfaces. If they find the ground, they'll keep 'running' low to the ground and spread a gigantic soft root system. If it finds a wall/tree/fence/brick, chances are it will find a nice bit of sunlight if it grows high enough. It's ground roots will dig in, going deep but not spreading out. It's a little harder to imagine ivy not having access to soil (maybe there's a pine needle covering - we usually see it in potted ivy that only has a tiny bit of soil), and it will clump in a tiny shrub as the 'air roots' harden and the vine itself acts more as a stem.

It's really fun to clone. ; - D
posted by cowbellemoo at 7:17 PM on July 10, 2006

Do you know of any highly variant plant for which exhaustive behavioral studies have been done?

As a matter of fact, I do. I went to graduate school (my degree is in Ecology, but I was in the Botany department) with a woman who studied phenotypic plasticity in an aquatic plant, Vallisneria americana, common name wildcelery (not related to the vegetable). Vallisneria will grow into wildly different forms depending on the stream conditions it's growing in.
posted by mcstayinskool at 8:21 PM on July 10, 2006

There's something in the front yard that starts out as a shrub, but if it runs into a wall, it will grow up the wall like a vine. They say if you take cuttings from the vine part, they will always try to vine up. I cannot remember what it's called, but some common landscaping bush.
posted by unrepentanthippie at 4:58 AM on July 11, 2006