Stinging Nettle, Urtica dioica, a wild herb plant that is edible and has medicinal properties. There are thin needles on the stems and leaves, double click on the photo to enlarge.
While on a nature walk with my twelve year old son at the site of his wilderness school (a homeschool program) I asked him to show me some stinging nettle as I've never seen it in real life. Well, I might have seen it in my garden path last year but I'm not sure. He knew right where it was (taught to him by his naturalist teachers).
Photo taken 4/22/10 by ChristineMM in Fairfield County, Connecticut.