WordNet (r) 3.0 (2006):

subclass Hamamelidae
    n 1: a group of chiefly woody plants considered among the most
         primitive of angiosperms; perianth poorly developed or
         lacking; flowers often unisexual and often in catkins and
         often wind pollinated; contains 23 families including the
         Betulaceae and Fagaceae (includes the Amentiferae);
         sometimes classified as a superorder [syn: Hamamelidae,
         subclass Hamamelidae]