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205. Ischaemum Linnaeus, Sp. Pl. 2: 1049. 1753.

鸭嘴草属 ya zui cao shu

Authors: Bi-xing Sun & Sylvia M. Phillips

Perennial, or sometimes annual. Culms often decumbent and much branched. Leaf blades linear to lanceolate, narrowed to ligule, sometimes pseudopetiolate; ligule membranous; sheath auricles often present. Inflorescence of paired racemes, or occasionally subdigitate, terminal and axillary, exserted or sometimes supported by a spatheole; racemes 1-sided, when paired often locked back to back and appearing as a single cylindrical raceme, spikelets of a pair similar or not; rachis internodes and pedicels stoutly linear to thickly clavate, U-shaped or triquetrous in cross section. Sessile spikelet dorsally compressed; callus truncate or obtuse, inserted into hollowed internode apex; lower glume papery to leathery, shallowly convex or almost flat, 2-keeled or rounded on flanks, sometimes winged, often rugose; upper glume boat-shaped, awnless or with straight awn from apex; lower floret male, well developed with palea; upper lemma usually deeply 2-lobed, awned from sinus, rarely awnless; awn geniculate, glabrous. Pedicelled spikelet as large as sessile or much smaller, upper lemma sometimes geniculately awned.

About 70 species: throughout the tropics but mainly in Asia, especially India; 12 species (one endemic) in China.

1 Margins of lower glume of sessile spikelet broadly rounded in lower part, narrowly inflexed and keeled above, not coarsely rugose or knobbly   (2)
+ Margins of lower glume of sessile spikelet narrowly and evenly inflexed and keeled along entire length, often coarsely rugose or knobbly   (8)
2 (1) Spikelets of a pair without obvious awns, or only sessile spikelet awned   (3)
+ Spikelets of a pair both clearly awned   (5)
3 (2) Inflorescence base enclosed in uppermost sheath; plant strongly rhizomatous.   1 I. muticum
+ Inflorescence long exserted from uppermost sheath; plant loosely tufted   (4)
4 (3) Racemes villous; sessile spikelet 8–10 mm.   2 I. anthephoroides
+ Racemes glabrous; sessile spikelet 5.5–8 mm.   3 I. aristatum
5 (2) Lower glume of sessile spikelet winged on keels, apex rounded, emarginate   (6)
+ Lower glume of sessile spikelet not winged on keels, apex sharply bicuspidate   (7)
6 (5) Racemes paired; rhizomes absent; culms less than 60 cm.   4 I. ciliare
+ Racemes (2–)3–6; rhizomes present; culms 60–100 cm.   5 I. polystachyum
7 (5) Spikelets ± glabrous; upper glume of sessile spikelet not winged on keel; callus hairs less than 1 mm.   6 I. timorense
+ Spikelets hispid; upper glume of sessile spikelet winged on keel; callus hairs ca. 2 mm.   7I I. thomsonianum
8 (1) Lower glume of sessile spikelet not transversely rugose or knobbly   (9)
+ Lower glume of sessile spikelet transversely rugose or knobbly on flanks   (10)
9 (8) Lower glume of sessile spikelet wingless, keels pilose; awn 1.8–2.5 cm.   8 I. aureum
+ Lower glume of sessile spikelet winged, glabrous; awn 1–1.2 cm.   9 I. setaceum
10 (8) Plant annual; lower glume of sessile spikelet coarsely rugose with 4–7 sharp transverse ridges across back.   10 I. rugosum
+ Plant perennial; lower glume of sessile spikelet with rounded knobs on keels in lower part, sometimes also with 2–4 weak ridges across back   (11)
11 (10) Culms up to 1 m tall; sessile spikelet 5–7 mm, awned, awn 1–1.5 mm.   11 I. barbatum
+ Culms 1–2 m tall; sessile spikelet 6.5–8 mm, awnless or awn less than 1 mm.   12 I. magnum

  • List of lower taxa


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