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208. Arthraxon P. Beauvois, Ess. Agrostogr. 111. 1812.
荩草属 jin cao shu
Authors: Shou-liang Chen & Sylvia M. Phillips
Batratherum Nees; Lucaea Kunth; Pleuroplitis Trinius.
Annual or perennial. Culms slender, much branched, often trailing, nodes bearded or infrequently glabrous. Leaf blades lanceolate to ovate, cordate, often clasping culm, usually pectinate-setose on lower margins; ligule membranous, hairy on margin and back. Inflorescence of subdigitate, slender, fragile racemes, these terminal on culms and branches, not spathate; rachis internodes and pedicels filiform to linear, glabrous or ciliate on angles; spikelets of a pair dissimilar, or spikelets apparently solitary. Sessile spikelet linear to lanceolate, dorsally or laterally compressed; callus short, truncate; lower glume membranous to leathery, back flat or convex, several-veined, with or without lateral keels, scaberulous to spinulose; upper glume boat-shaped, keel herbaceous, margins hyaline, apex acute to mucronate; lower floret reduced to an empty hyaline lemma; upper lemma hyaline, entire or shortly 2-toothed, awned from near base; awn geniculate, glabrous. Stamens 2 or 3. Caryopsis terete. Pedicelled spikelet variable, awnless, well developed, reduced, or represented by the pedicel only, sometimes almost completely suppressed. x = 9.
About 26 species: Old World tropics, mainly in India; introduced in America; 12 species (one endemic) in China.
Arthraxon is a rather isolated genus with no obvious close relatives, distinguished from the other awned Andropogoneae by its broad, clasping leaf blades on slender, branching culms, together with a sub-basally awned fertile lemma. It is superficially similar to Microstegium, but that genus has awned pedicelled spikelets.
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| 1 |
Lower glume of sessile spikelet laterally 2-keeled, margins inflexed; perennial; anthers 3 |
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(2) |
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Lower glume of sessile spikelet without lateral keels, margins flat; annual or perennial; anthers 2 or 3 |
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(4) |
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| 2 (1) |
Keels of lower glume stoutly pectinate-spinose, intercarinal veins usually muricate; leaf blades pubescent; uppermost sheath inflated, spathelike. |
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1 A. echinatus |
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Keels of lower glume tuberculate or almost smooth, intercarinal veins smooth or scaberulous; leaf blades glabrous or sparsely hispid; uppermost sheath tightly cylindrical |
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(3) |
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| 3 (2) |
Plant with knotty rootstock covered in velvety scales; lower glume of sessile spikelet with 2 rows of tubercles along each keel, intercarinal veins obscure except near apex. |
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2 A. prionodes |
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Plant with spreading branching rhizomes; lower glume of sessile spikelet with 1 row of tubercles along each keel, intercarinal veins visible from base. |
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3 A. epectinatus |
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| 4 (1) |
Sessile spikelets 1.2–2.1 mm. |
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6 A. junnarensis |
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Sessile spikelets 2–8 mm |
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(5) |
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| 5 (4) |
Pedicelled spikelets present, at least at raceme apex |
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(6) |
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Pedicelled spikelets absent or vestigial, represented by the pedicel only, this sometimes reduced to a minute stump |
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(8) |
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| 6 (5) |
Sessile spikelets lanceolate, strongly scabrid to spinulose. |
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7 A. hispidus |
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Sessile spikelets smooth to scaberulous |
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(7) |
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| 7 (6) |
Lower glume of sessile spikelet linear, obscurely veined, smooth below middle. |
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11 A. lancifolius |
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Lower glume of sessile spikelet lanceolate or elliptic, strongly 6- or 7-veined with deep grooves between. |
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12 A. microphyllus |
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| 8 (5) |
Stamens 2 |
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(9) |
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Stamens 3 |
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(10) |
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| 9 (8) |
Culms 10–30 cm tall; lower glume 5–9-veined. |
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7 A. hispidus |
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Culms 30–60 cm tall; lower glume 9–11-veined. |
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8 A. multinervis |
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| 10 (8) |
Sessile spikelets 4–8 mm; anthers (1.5–)2–3.5 mm |
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(11) |
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Sessile spikelets 2.8–4.2 mm; anthers 0.4–2 mm |
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(12) |
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| 11 (10) |
Raceme bases terete, pubescent all over; upper glume broad, leathery, hyaline margins 0.1–0.2 mm; lemma margins ciliate. |
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4 A. castratus |
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Raceme bases flattened on inner face, only flattened surface pubescent; upper glume narrow, leathery, hyaline margins 0.6–0.7 mm; lemma margins glabrous. |
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5 A. typicus |
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| 12 (10) |
Sessile spikelets apparently awnless; anthers 1.5–2 mm. |
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9 A. submuticus |
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Sessile spikelets with exserted awn; anthers 0.4–0.5 mm. |
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10 A. nudus |
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List of lower taxa
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