thimbleweed

from WordNet (r) 3.0 (2006)

thimbleweed
    n 1: a common North American anemone with cylindrical fruit
         clusters resembling thimbles [syn: {thimbleweed}, {Anemone
         cylindrica}]

from The Collaborative International Dictionary of English v.0.48

Thimbleweed \Thim"ble*weed`\, n. (Bot.)
   Any plant of the composite genus {Rudbeckia}, coarse herbs
   somewhat resembling the sunflower; -- so called from their
   conical receptacles.
   [1913 Webster]