Excerpts from Jim Conrad's
from the April 17, 2005 Newsletter issued from the Sierra Nevada foothills
somewhat east of Placerville, California, USA
POISON OAK & BEYOND
Poison Oak is about as abundant here as Poison Ivy back in the East. Moreover, here in early spring it's so attractive that you're tempted to pick a sprig and taste it. The leaves are glossy, succulent and reddish, a little like Oak-leafed Lettuce. You can see such leaves here.
When I was a kid I learned that "Poison Ivy grows in the East, Poison Oak in the West." Now I know it's more complex than that.
For instance, we have Pacific Poison Oak here, TOXICODENDRON DIVERSILOBUM, which doesn't make it as far east as Utah, and then in the US Southeast there's Atlantic Poison Oak, T. PUBESCENS. Eastern Poison Ivy, T. RADICANS, occurs in eastern North America, but there's also a Western Poison Ivy, T. RYDBERGII found in both the West (but not California) and the northeastern and north-central states. Maps showing the distributions of these species appear midway down the page at http://plants.usda.gov/cgi_bin/topics.cgi?earl=plant_profile.cgi&symbol=TOXIC.