Dog's mercury (Mercurialis perennis)

Collins, 144; Readers Digest, 197

This low downy perennial enjoys  woods and shaded places where it flowers with green stalked tassels from February to May.  The plant is extremely poisonous to animals and humans.  Wild animals tend to avoid this plant but cattle that eat it can linger for long periods before dying.  The name derives from the fact that during mediaeval times it was considered worthless and only fit for dogs.

See also: http://www.botanical.com/botanical/mgmh/m/merdog31.html

Photograph taken in March showing female flowers?