The Collaborative International Dictionary of English v.0.48:

Joe-Pye weed \Joe`-Pye" weed`\ (Bot.)
   A tall composite plant of the genus Eupatorium (Eupatorium
   purpureum), with purplish flowers, and whorled leaves.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Trumpetweed \Trump"et*weed`\, n. (Bot.)
   (a) An herbaceous composite plant (Eupatorium purpureum),
       often having hollow stems, and bearing purplish flowers
       in small corymbed heads.
   (b) The sea trumpet.
       [1913 Webster]

WordNet (r) 3.0 (2006):

Eupatorium purpureum
    n 1: North American herb having whorled leaves and terminal
         clusters of flowers spotted with purple [syn: Joe-Pye
         weed, purple boneset, trumpet weed, marsh milkweed,
         Eupatorium purpureum]