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FOC | Family List | FOC Vol. 22 | Poaceae

217. Hemarthria R. Brown, Prodr. 207. 1810.

牛鞭草属 niu bian cao shu

Authors: Bi-xing Sun & Sylvia M. Phillips

Perennial, rarely annual. Culms usually prostrate and rooting at lower nodes. Leaf blades linear, flat; ligule narrow, membranous, margin ciliate. Inflorescence composed of single axillary racemes; racemes solitary or in groups in upper leaf axils, dorsiventral, articulation line usually oblique but racemes tough, not or very tardily disarticulating; rachis internodes thickened, oblong-angular, adnate to adjacent pedicel. Sessile spikelet appressed to hollow in rachis, dorsally compressed (terete in H. sibirica); callus obtuse to cuneate, rarely truncate; lower glume narrowly elliptic, rigidly herbaceous to leathery, smooth, marginally 2-keeled, indistinctly winged above, obtuse to caudate or rarely 2-cleft; upper glume sometimes adnate to internode, mucronate or awned; lower floret barren, without palea; upper floret bisexual, with entire awnless lemma. Pedicelled spikelet similar to sessile, but base truncate and lacking callus; pedicel similar to adnate rachis internode, junction marked by a line. x = 9, 10.

Fourteen species: tropical and subtropical regions of the Old World; introduced in America; six species (one endemic) in China.

This is a genus of aquatic or semi-aquatic grasses concentrated in SE Asia. At first sight it is difficult to distinguish the sessile and pedicelled spikelets because they look very similar and, since the pedicel is fused to the rachis internode, both spikelets are in effect sessile. However, the sessile spikelet of a pair can be distinguished by its basal callus, which normally has an oblique articulation line beneath it. The strongly bilateral racemes have all the sessile spikelets on one side and all the pedicelled spikelets on the other.

1 Sessile spikelets 8–15 mm.   1 H. longiflora
+ Sessile spikelets less than 8 mm   (2)
2 (1) Lower glume of sessile spikelet evenly narrowed to acuminate apex; upper glume of pedicelled spikelet caudate-aristate   (3)
+ Lower glume of sessile spikelet with rounded apex, usually with subapical constriction; upper glume of pedicelled spikelet acute to acuminate   (4)
3 (2) Leaf blades 3–8 mm wide; lower glume of sessile spikelet leathery; lower glume of pedicelled spikelet distally smooth along margins.   2 H. vaginata
+ Leaf blades 1–2 mm wide; lower glume of sessile spikelet papery; lower glume of pedicelled spikelet distally scabrid along margins.   3 H. humilis
4 (2) Racemes subterete; articulations of rachis transverse; callus short, truncate.   4 H. sibirica
+ Racemes dorso-ventrally compressed; articulations of rachis oblique; callus triangular   (5)
5 (4) Sessile spikelet 3–5 mm; lower glume margins distally smooth; leaf blades rounded at base.   5 H. compressa
+ Sessile spikelet 5–7 mm; lower glume margins distally scabrid; leaf blades subcordate at base.   6 H. altissima

Lower Taxa


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