The Collaborative International Dictionary of English v.0.48:

Bunch grass \Bunch" grass`\ (Bot.)
   A grass growing in bunches and affording pasture. In
   California, Atropis tenuifolia, Festuca scabrella, and
   several kinds of Stipa are favorite bunch grasses. In Utah,
   Eriocoma cuspidata is a good bunch grass.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bunch grass
    n 1: any of various grasses of many genera that grow in tufts or
         clumps rather than forming a sod or mat; chiefly of western
         United States [syn: bunchgrass, bunch grass]