The Collaborative International Dictionary of English v.0.48:

Ice plant \Ice" plant`\ (Bot.)
   A plant (Mesembryanthemum crystallinum), sprinkled with
   pellucid, watery vesicles, which glisten like ice. It is
   native along the Mediterranean, in the Canaries, and in South
   Africa. Its juice is said to be demulcent and diuretic; its
   ashes are used in Spain in making glass.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ice plant
    n 1: Old World annual widely naturalized in warm regions having
         white flowers and fleshy foliage covered with hairs that
         resemble ice [syn: ice plant, icicle plant,
         Mesembryanthemum crystallinum]