thim·ble·weed /ˈθɪmbəlˌwid/
  Thim·ble·weed n. Bot. Any plant of the composite genus Rudbeckia, coarse herbs somewhat resembling the sunflower; -- so called from their conical receptacles.
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  thimbleweed
       n : a common North American anemone with cylindrical fruit
           clusters resembling thimbles [syn: Anemone cylindrica]