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Annuals, or rhizomatous or tufted perennial grasses. Culms erect, ascending or decumbent. Leaf-blades linear to linear-lanceolate, leaf-sheath terete or compressed, ligule membranous, lacerate or ciliate. Inflorescence panicle, of varied shape and size, occasionally condendesed. Spikelets usually ovate to elliptic, more or less dorsally compressed, disarticulation below glumes; lower glume shorter than upper; upper glume typically equalling the lower lemma, usually as long as spikelets; lower floret male or barren; upper floret bisexual, upper lemma more or less of spikelet length, subcoriaceous to coriaceous, margins inrolled and clasping the palea; lodicules 2; stamens 3. Caryopsis ellipsoid.

Key to the species

Serial Key Reference
1a. Leaf-blades ovate-lanceolate; spikelets asymmetrical P. brevifolium
1b. Leaf-blades linear to lanceolate; spikelets symmetrical 2
2a. Upper lemma transversely rugose P. maximum
2b. Upper lemma smooth 3
3a. Spikelets 4.5-5.5 mm long, sharply acute, ovate to elliptic in back view P. miliaceum
3b. Spikelets up to 3.5 mm long 4
4a. Spikelets 1.5- 2.0 mm long. Dwarf grass P. humile
4b. Spikelets over 2 mm long 5
5a. Lower glume cuspidate or cuspidate- acuminate; spikelets gaping at maturity P. curviflorum
5b. Lower glume not cuspidate-acuminate; spikelets not gaping at maturity 6
6a. Spikelets narrowly lanceolate to lanceolate-oblong, acute 7
6b. Spikelets oblong, ovate-oblong to elliptic, acute or obtuse 9
7a. Lower glume ovate, acute or obtuse, 1/3 the length of the spikelet; spikelets 2.0-2.5 mm long; panicle branches densely spiculate P. auritum
7b. Lower glume orbicular, rotundate or truncate, 1/6th to 1/4th the length of the spikelet; spikelets 2.5-4.0 mm long; panicle-branches loosely to closely spiculate 8
8a. Culms spongy, floating; spikelets 3 mm long or more, narrowly lanceolate; leaf-blade broad, flat P. dichotomiflorum
8b. Culms tough, rhizomatous; spikelets less than 3 mm long, lanceolate to lanceolate-oblong; leaf-blade narrow, stiff, often involute P. repens
9a. Lower glume ¼ to 1/3 the length of the spikelet 10
9b. Lower glume ½ to ¾ the length of the spikelet or more 11
10a. Perennials; spikelets persistent, larger; panicle contracted; lower glume orbicular-apiculate P. antidotale
10b. Annuals; spikelets deciduous, smaller; panicle effuse, lower glume ovate-apiculate P. sumatrense ssp. psilopodium
11a. Annuals; spikelets acute. Dwarf grasses P. atrosanguineum
11b. Perennials; spikelets obtuse 12
12a. Lower floret epaleate; leaf-base deeply cordate; leaf-margins usually, but not always, pectinately ciliate below P. notatum
12b. Lower floret paleate; leaf-base not cordate, rounded, narrow; leaf-margins not pectinately ciliate below 13
13a. Inflorescence globular or ellipsoidal; spikelets often very crowded; glumes and lemmas dull, matt, with strongly marked nerves; branches and branchlets viscid; lower glume ¾ the length of the spikelet P. incomtum
13b. Inflorescence panduriform or fan-shaped; spikelets not crowded; glumes and lemmas shining, not strongly nerved; branches and branchlets smooth; lower glume ½ the length of the spikelet P. sarmentosum