Moonseed, also known as
Yellow parilla, is a poisonous plant that is dangerously similar to
wild grapes.
It has heart-shaped
leaves with long
stalks, similar to that of a grape. It is a climbing
vine, like a grape, however, it
twines around whatever it is securing itself to, rather than sending out
tendrils. It has clusters of purplish-black fruit, again similar to grape. Moonseed is found throughout North America.
Moonseed and grapes even ripen at the same time, early summer. They grow in the same places, thickets, stream banks, and woods. Moonseed contains an Alkaloid dauricine. It is highly toxic, the convulsions are a dead giveaway that you've been poisoned. It could prove fatal.
Now that I've scared the pants off anyone who likes to eat wild grape, I will tell you how to tell these plants apart. Firstly, the stems do not get as woody as grapes, they are lacking the loose bark as well. The final method to differentiate them is also the most precise, the fruit of the Moonseed contains a single flat, crescent-shaped seed. Grapes contain a few little seeds. So I guess what I'm trying to say is, cut your wild grapes in half before you eat them.
Sources:
Hall, Alan. The Wild Food Trail Guide. Holt, Rhinehart, and Winston. 1945.