Source : Webster's Revised Unabridged Dictionary (1913)

Joe-Pye weed \Joe`-Pye" weed`\ (Bot.)
   A tall composite plant of the genus {Eupatorium} ({E.
   purpureum}), with purplish flowers, and whorled leaves.

Source : WordNet®

Joe-Pye weed
     n 1: North American herb having whorled leaves and terminal
          clusters of flowers spotted with purple [syn: {purple
          boneset}, {trumpet weed}, {marsh milkweed}, {Eupatorium
          purpureum}]
     2: North American herb having whorled leaves and terminal
        clusters of small pinkish or purple flower heads [syn: {spotted
        Joe-Pye weed}, {Eupatorium maculatum}]