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Annual or perennial grasses, culms tufted or with creeping rhizomes or stolons.  Leaf-blades linear to linear-lanceolate, ligules membranous. Inflorescence of spike-like racemes, single or digitate or racemosely arranged, rachis triquetrous. Spikelets orbicular, secund, plano-convex, 2-4 rowed, disarticulating below glumes; glumes unequal, lower glume absent, upper glume herbaceous, as long as spikelets; lower floret sterile, upper floret perfect; lower lemma herbaceous, flat; upper lemma indurate, margin inrolled; palea usually absent in lower floret. Lodicules 2, truncate. Stamens 3. Caryopsis elliptic to orbicular.

Key to the species

Serial Key Reference
1a. Spikelets arranged in four rows upon a broad rachis P. longifolium
1b. Spikelets arranged in two rows 2
2a. Spikelets fringed with fine white hairs from the margins of the upper glume P. conjugatum
2b. Spikelets glabrous or pubescent, not ciliate on the margins of the upper glume 3
3a. Plants tufted; racemes 3-5, subdigitate or on a short axis; spikelets rotundate-elliptic, broadly obovate or suborbicular, obtuse, solitary or paired P. scrobiculatum
3b. Plants with long creeping stolons and/or rhizomes; racemes 2 (-3), paired; spikelets lanceolate to ovate or obovate, solitary 4
4a. Upper glume pubescent; spikelets plano-convex, obovate oblong, twice as long as broad; lower lemma with prominent median nerve P. distichum
4b. Upper glume entirely glabrous; spikelets strongly flattened, lanceolate oblong, thrice as long as broad; lower lemma faintly nerved P. vaginatum