Twice in the last year I've fished at lakes in the D/FW area and gotten a rash of some sort on one of my legs, just about my ankle. The rash looks like a bright red, slightly purplish sunburn, but does not itch at all. It goes away after a week.

If it were poison ivy, I would expect it to itch and cause blisters, but it did neither. Anybody know what kind of plant can cause this?

Try to go here and post that, see what they say.
http://en.allexperts.com/q/Dermatology-1011/

Thanks.