■ Introduced from Europe in the 1800s, probably for medicinal purposes.
■ Grows from New England south to Virginia, and west to Kansas and Nebraska.
■ Average plant produces 400-500 seeds, which remain viable in the ground for up to five years.
■ Two-year life cycle: Clusters of heart-shaped, notched leaves lie close to the ground the first year; stalks grow 2 to 3½ feet high the following year, topped with clusters of small white flowers, followed by shiny black seed pods.
■ Kills all plants in its vicinity, including those needed by butterflies and moths.
SOURCES: Plant Conservation Alliance; Nature Conservancy