The Collaborative International Dictionary of English v.0.48:

Water chickweed \Wa"ter chick"weed`\ (Bot.)
   A small annual plant (Montia fontana) growing in wet places
   in southern regions.
   [1913 Webster]

WordNet (r) 3.0 (2006):

water chickweed
    n 1: small Indian lettuce of northern regions [syn: blinks,
         blinking chickweed, water chickweed, Montia
         lamprosperma]