The Collaborative International Dictionary of English v.0.48:

Air plant \Air" plant`\ (Bot.)
   A plant deriving its sustenance from the air alone; an
   a["e]rophyte.
   [1913 Webster]

   Note: The "Florida moss" (Tillandsia, many tropical
         orchids, and most mosses and lichens are air plants.
         Those which are lodged upon trees, but not parasitic on
         them, such as the Spanish moss Tillandsia
         usneoides), are epiphytes.
         [1913 Webster]

WordNet (r) 3.0 (2006):

air plant
    n 1: plant that derives moisture and nutrients from the air and
         rain; usually grows on another plant but not parasitic on
         it [syn: air plant, epiphyte, aerophyte, epiphytic
         plant]