The Collaborative International Dictionary of English v.0.48:

Xyris \Xy"ris\, n. [L., a kind of Iris, Gr. ?, fr. ? a razor.]
   (Bot.)
   A genus of endogenous herbs with grassy leaves and small
   yellow flowers in short, scaly-bracted spikes; yellow-eyed
   grass. There are about seventeen species in the Atlantic
   United States.
   [1913 Webster] Xyst

WordNet (r) 3.0 (2006):

Xyris
    n 1: chiefly American marsh plants, having usually yellow
         flowers [syn: Xyris, genus Xyris]