WordNet (r) 3.0 (2006):

rock brake
    n 1: any of several small lithophytic ferns of tropical and warm
         temperate regions [syn: cliff brake, cliff-brake, rock
         brake]
    2: dwarf deciduous lithophytic ferns
    3: chiefly lithophytic or epiphytic fern of North America and
       east Asia [syn: rock polypody, rock brake, American wall
       fern, Polypodium virgianum]