Tansy, Tanacetum vulgare L., contains a violent, irritant, narcotic poison, producing spasms and convulsions, but is very rarely eaten by animals. It was introduced into this country from Europe, and has escaped from gardens in various places.

It is a bitter and strong-scented herb, two to four feet high, with tough parsley-like leaves. The heads, each containing many yellow, tubular florets and few ray florets, are borne in dense flat corymbs.