WordNet (r) 3.0 (2006):

Conoclinium coelestinum
    n 1: rhizomatous plant of central and southeastern United States
         and West Indies having large showy heads of clear blue
         flowers; sometimes placed in genus Eupatorium [syn:
         mistflower, mist-flower, ageratum, Conoclinium
         coelestinum, Eupatorium coelestinum]