Water
hemlock, or cicuta douglasii, is an extremely
poisonous herb. Water hemlock grows up to two meters high, has
hollow stems, and delicate white flowers not unlike
Queen Anne's Lace. It has narrow, jagged leaves, alternating along the stems. The roots are the most poisonous part, and remain potently
toxic even when dried, but all parts of the plant are toxic. It's been nicknamed "cowbane" because it can kill livestock grazing on even a small portion of it in 15 minutes. Humans have died shortly after only one bite of the deadly root, which strongly resembles
parsnips.
At a summer camp I used to work at, one of the kids fell in to a patch of water hemlock once. We washed him off with the fire hose. Seriously. We unhooked the fire hose from the pump in the lake where it was dutifully filling the well, put a pair of goggles on the poor kid, and blasted away. Water hemlock is seriously nasty shit.