Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Spikelets ovate, elliptic, obovate, or orbicular, planoconvex, short-pediceled or subsessile, solitary or in pairs, forming a 2-rowed or 4-rowed, usually spike-like raceme on one side of a flattened or triquetrous rachis; first glume usually none, very short when present; second glume and sterile lemma of about equal length, 2–7-veined, acute to rounded; fertile lemma indurate, smooth or minutely papillose, its margins inrolled over the indurate palea; ours perennial (except P. boscianum), usually tufted or branched from the base, with usually soft lvs, membranous ligule, and a terminal infl of 1–many racemes along a common axis, often with additional racemes on axillary peduncles from the upper sheaths. 250, mainly trop. and warm-temp.