The Collaborative International Dictionary of English v.0.48:

dallis grass \dallis grass\, dallisgrass \dallisgrass\n.
   a tall tufted perennial tropical American grass (Paspalum
   dilatatum) naturalized as pasture and forage grass in the
   southern U.S.

   Syn: paspalum, Paspalum dilatatum.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

dallisgrass
    n 1: tall tufted perennial tropical American grass naturalized
         as pasture and forage grass in southern United States [syn:
         dallisgrass, dallis grass, paspalum, Paspalum
         dilatatum]