joe-pye weed

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

• noun Any of several tall North American plants of the genus Eupatorium of the composite family, having whorled leaves and clusters of small pinkish or purplish flower heads.

from The Century Dictionary.

• noun An American plant, Eupatorium purpureum, a tall weed with corymbs of purple flowers, common in low ground. Also called trumpetweed. See Eupatorium.

from the GNU version of the Collaborative International Dictionary of English.

• (Bot.) A tall composite plant of the genus Eupatorium (Eupatorium purpureum), with purplish flowers, and whorled leaves.

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

• noun A plant of the genus Eutrochium.

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

• noun North American herb having whorled leaves and terminal clusters of flowers spotted with purple
• noun North American herb having whorled leaves and terminal clusters of small pinkish or purple flower heads