Texas Gardening: need help identifying weed please?, 1 by jerrytx

jerrytx wrote:
I am trying to I.D. the weed found in my garden bed. This rascal upon touching any part of it, causes a "pins & needles" affect on the skin, and stays in that state for several days no matter how well, or often you wash the skin! I know the pic is a little (?) grainy, but the leaf is heart shaped, and has a "sawtooth" edge to it. Any help would be appreciated.

p.s. I work at a community garden where I ALSO have encountered this weed..