Source : Webster's Revised Unabridged Dictionary (1913)

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

   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, are epiphytes.

Source : WordNet®

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