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.