blue cohosh

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A perennial herb (Caulophyllum thalictroides) of eastern North America, having one or two compound leaves, small yellow-green or purplish flowers, and blue berrylike seeds.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A perennial American herb (Caulophyllum thalictroides), whose rootstock is used in medicine.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun tall herb of eastern North America and Asia having blue berrylike fruit and a thick knotty rootstock formerly used medicinally