Princeton's WordNet

1. Hamamelidae, subclass Hamamelidae(noun)

   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