Yes, Chichicastenango translated means "Place of the Poison Trees" and the trees do exist.
"Chichicaste" is the plant's name and "Tenango" indicates a place. Our guide told us that chichicaste trees are commonly planted around tobacco plantations to keep intruders out. The leaves are kind of fuzzy, and seem to invite you to touch them -- but I decided to just believe the story and not check it out firsthand. I hear that it is painful.