The Collaborative International Dictionary of English v.0.48:

evening-snow \evening-snow\ n.
   small California annual (Linanthus dichotomus) with white
   flowers.

   Syn: evening snow, Linanthus dichotomus.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

evening-snow
    n 1: small California annual with white flowers [syn: evening-
         snow, Linanthus dichotomus]