The Collaborative International Dictionary of English v.0.48:

Dayflower \Day"flow`er\ (-flou`[~e]r), n. (Bot.)
   A genus consisting mostly of tropical perennial herbs
   (Commelina), having ephemeral flowers.
   [1913 Webster]

WordNet (r) 3.0 (2006):

dayflower
    n 1: any plant of the family Commelinaceae [syn: spiderwort,
         dayflower]