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FOC | Family List | FOC Vol. 22 | Poaceae

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.

1 Lower glume of sessile spikelet laterally 2-keeled, margins inflexed; perennial; anthers 3   (2)
+ Lower glume of sessile spikelet without lateral keels, margins flat; annual or perennial; anthers 2 or 3   (4)
2 (1) Keels of lower glume stoutly pectinate-spinose, intercarinal veins usually muricate; leaf blades pubescent; uppermost sheath inflated, spathelike.   1 A. echinatus
+ Keels of lower glume tuberculate or almost smooth, intercarinal veins smooth or scaberulous; leaf blades glabrous or sparsely hispid; uppermost sheath tightly cylindrical   (3)
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.   2 A. prionodes
+ Plant with spreading branching rhizomes; lower glume of sessile spikelet with 1 row of tubercles along each keel, intercarinal veins visible from base.   3 A. epectinatus
4 (1) Sessile spikelets 1.2–2.1 mm.   6 A. junnarensis
+ Sessile spikelets 2–8 mm   (5)
5 (4) Pedicelled spikelets present, at least at raceme apex   (6)
+ Pedicelled spikelets absent or vestigial, represented by the pedicel only, this sometimes reduced to a minute stump   (8)
6 (5) Sessile spikelets lanceolate, strongly scabrid to spinulose.   7 A. hispidus
+ Sessile spikelets smooth to scaberulous   (7)
7 (6) Lower glume of sessile spikelet linear, obscurely veined, smooth below middle.   11 A. lancifolius
+ Lower glume of sessile spikelet lanceolate or elliptic, strongly 6- or 7-veined with deep grooves between.   12 A. microphyllus
8 (5) Stamens 2   (9)
+ Stamens 3   (10)
9 (8) Culms 10–30 cm tall; lower glume 5–9-veined.   7 A. hispidus
+ Culms 30–60 cm tall; lower glume 9–11-veined.   8 A. multinervis
10 (8) Sessile spikelets 4–8 mm; anthers (1.5–)2–3.5 mm   (11)
+ Sessile spikelets 2.8–4.2 mm; anthers 0.4–2 mm   (12)
11 (10) Raceme bases terete, pubescent all over; upper glume broad, leathery, hyaline margins 0.1–0.2 mm; lemma margins ciliate.   4 A. castratus
+ Raceme bases flattened on inner face, only flattened surface pubescent; upper glume narrow, leathery, hyaline margins 0.6–0.7 mm; lemma margins glabrous.   5 A. typicus
12 (10) Sessile spikelets apparently awnless; anthers 1.5–2 mm.   9 A. submuticus
+ Sessile spikelets with exserted awn; anthers 0.4–0.5 mm.   10 A. nudus

  • List of lower taxa


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