thimbleweed

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

• noun Any of several North American anemones having cylindrical, thimblelike fruit clusters.

from The Century Dictionary.

• noun An American anemone, Anemone Virginiana.

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

• noun (Bot.) Any plant of the composite genus Rudbeckia, coarse herbs somewhat resembling the sunflower; -- so called from their conical receptacles.

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

• noun botany Any of various plants whose heads resemble thimbles, including Rudbeckia laciniata, Anemone virginiana, and Anemone cylindrica.

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

• noun a common North American anemone with cylindrical fruit clusters resembling thimbles