Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Spikelets 1-fld, strongly flattened, articulated below the glumes, closely or loosely imbricate in 2 rows on 2 sides of a triangular rachis; glumes unequal, narrow, 1-veined, acute, acuminate, or awned, the second (exterior in the spike) exceeding the lemma; lemma firm, keeled, awnless, obscurely veined; palea equaling or usually exceeding the lemma; perennial, usually colonial from stout, scaly rhizomes, with a few to many dense, one-sided spikes appressed to spreading along a common axis; ligule a band of hairs; good seed only sparingly produced. 15, New World and w. Europe and Afr.