荩草 jin cao

Annual. Culms slender, sprawling, decumbent, rooting from lower nodes, weakly ascending up to 30 cm or more. Leaf sheaths glabrous to tuberculate-hispid, margin ciliate; leaf blades ovate to narrowly ovate, 2–5 cm × 6–15 mm, glabrous or hispid, base amplexicaul, margins pectinate-setose at least around base, apex sharply acute; ligule 0.5–3 mm. Racemes 2–10 or more, 1.5–4 cm, pale green or purple; rachis internodes (1/2–) 2/3–3/4 length of sessile spikelets, glabrous or sparsely to densely pilose, hairs less than 0.5 mm. Sessile spikelet 3–5 mm; lower glume lanceolate, weakly convex, margins not inflexed, 6–9-veined, veins scabrid-hispidulous to spinulose; upper glume slightly longer than lower, apex cuspidate; awn up to 11 mm, well developed and exserted from glumes, or sometimes reduced and included; palea absent. Anthers 2, 0.7–1 mm. Pedicelled spikelet usually absent; pedicel reduced to a minute stump, sometimes up to 2 mm or more at raceme apex, glabrous, sparsely ciliate, or infrequently densely pilose. Fl. and fr. Sep–Nov. 2n = 10, 18, 36.

Streamsides, damp meadows, among crops, other moist places; 100–2300 m. Anhui, Fujian, Guangdong, Guizhou, Hainan, Hebei, Heilongjiang, Henan, Hubei, Jiangsu, Jiangxi, Nei Mongol, Ningxia, Shaanxi, Shandong, Sichuan, Taiwan, Xinjiang, Yunnan, Zhejiang [Bhutan, India, Indonesia, Japan, Kazakhstan, Korea, Kyrgyzstan, Malaysia, Nepal, New Guinea, Pakistan, Philippines, Russia (Far East), Sri Lanka, Tajikistan, Thailand, Uzbekistan; Africa, SW Asia (Caucasus, Oman), Australia].

Arthraxon hispidus is an extremely polymorphic, polyploid species, to which many names have been applied, both at specific and infraspecific rank. It is now a widespread weed, occurring in many warm-temperate and tropical parts of the world.

Arthraxon hispidus is based on a gathering from Japan with rather small (ca. 3.5 mm), spinulose spikelets and glabrous raceme internodes and pedicel stumps. Arthraxon micans is based on a gathering from NE India with slightly longer (ca. 4.2 mm), merely scabrid spikelets and densely pilose internodes and pedicels. These two entities are often maintained as separate species. While populations at the margins of the distribution of this widespread taxon are often fairly uniform, over the main part of its distribution in SE Asia and China there is every possible combination of characters. It has proved impossible to recognize more than one species in China.

The awn is usually well developed and clearly exserted, but there is continuous variation through more shortly awned forms to those with the awn included within the glumes, thereby making the spikelets appear awnless. The name Arthraxon hispidus var. cryptatherus has been applied in China to apparently awnless forms, but in fact the type of the species name, from Japan, has included awns. Arthraxon langsdorffii is based on a Japanese specimen with well-exserted awns.

Pubescence of the rachis internodes and pedicels, spikelet length, and degree of development of spinules on the lower glume are also very variable and without clear discontinuities. Spikelet length given here applies to specimens seen from China. Elsewhere, spikelets may be as long as ca. 8 mm. Infrequently, lanceolate pedicelled spikelets up to 3.5 mm are present at the raceme apex, including on the type of Arthraxon micans. Such specimens are easily distinguished from A. lancifolius by their flatter, broader, spinulose sessile spikelets.