The Collaborative International Dictionary of English v.0.48:

Oxalis \Ox"a*lis\, n. [L., a kind of sorrel, Gr. 'oxali`s, fr.
   'oxy`s sharp, pungent, acid.] (Bot.)
   A genus of plants, mostly herbs, with acid-tasting
   trifoliolate or multifoliolate leaves; -- called also wood
   sorrel.
   [1913 Webster]

WordNet (r) 3.0 (2006):

oxalis
    n 1: any plant or flower of the genus Oxalis [syn: oxalis,
         sorrel, wood sorrel]