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177. Pennisetum Richard, Syn. Pl. 1: 72. 1805.

狼尾草属 lang wei cao shu

Authors: Shou-liang Chen & Sylvia M. Phillips

Gymnotrix P. Beauvois.

Annuals or perennials. Culms tufted or rhizomatous, prostrate to over 3 m tall. Leaf blades flat, folded or convolute; ligule a ciliate membrane. Inflorescence a spikelike panicle, cylindrical to subglobose; branches numerous, contracted into short clusters of one or more spikelets subtended by an involucre of bristles; involucres sessile or with a short basal stipe, deciduous with the spikelets at maturity leaving peduncle stumps or scars on the main axis; bristles slender, scabrous, sometimes plumose, simple or very rarely branched, very unequal, outer shorter, often innermost stouter and conspicuously exceeding the rest. Spikelets usually lanceolate, dorsally compressed, herbaceous, acute or obtuse, florets 2, glumes and lower lemma variable; glumes often small and not exceeding 1/2 spikelet length; lower lemma staminate or neuter, equaling spikelet or reduced; upper lemma equaling spikelet, herbaceous or indurated, obtuse to acute. x = 9.

About 80 species: throughout the tropics; 11 species (four endemic, four introduced) in China.

Pennisetum is a large and variable genus, but the bristly, spikelike inflorescence is always readily recognizable. The only other panicoid genus with a similar bristly inflorescence is Setaria, but in that genus the bristles are not deciduous with the spikelets, instead remaining on the rachis at maturity. The bristles are derived from reduced panicle branches.

Many species provide good forage. Several species, including Pennisetum glaucum in China, are used for food.

1 Inflorescence reduced to 2–4 spikelets within the uppermost leaf sheath; low sward-forming perennial.   1 P. clandestinum
+ Inflorescence spikelike, clearly exserted above the leaves   (2)
2 (1) Bristles of involucre obviously branched above base.   2 P. lanatum
+ Bristles of involucre unbranched or branched only at extreme base   (3)
3 (2) Inflorescence axis with sharp decurrent wings below each involucre; upper floret deciduous; bristles densely woolly with crinkled hairs.   3 P. polystachion
+ Inflorescence axis not winged; upper floret persistent; bristles glabrous or hairs not crinkled, often tubercle-based   (4)
4 (3) Culms robust, often 2 m or more; upper lemma indurated in lower half, membranous toward apex; anthers with apical tuft of hairs   (5)
+ Culms usually less than 1.5 m; upper lemma of uniform texture; anthers without apical tuft of hairs   (6)
5 (4) Perennial; bristles longer than spikelets.   4 P. purpureum
+ Annual; bristles shorter than spikelets.   5 P. glaucum
6 (4) Involucres with a basal 2–3 mm stipe; bristles glabrous.   6 P. alopecuroides
+ Involucres subsessile or basal stipe less than 1 mm; bristles glabrous or plumose   (7)
7 (6) Inflorescence axis glabrous; plant with long spreading rhizomes   (8)
+ Inflorescence axis puberulous to hirtellous; plant loosely tufted or base decumbent   (9)
8 (7) Bristles equaling or longer than spikelets.   7 P. flaccidum
+ Bristles shorter than spikelets (except longest).   8 P. sichuanense
9 (7) Bristles soft, numerous, plumose; leaf sheaths glabrous.   9 P. qianningense
+ Bristles stiff, mostly in a single whorl, glabrous or thinly plumose; lower leaf sheaths papillose-pilose   (10)
10 (9) Leaf blades 1.2–2 cm wide; inflorescence 20–30 cm.   10 P. longissimum
+ Leaf blades 0.2–1.2 cm wide; inflorescence less than 20 cm.   11 P. shaanxiense

  • List of lower taxa


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