Small Carpgrass

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.

This is a very common grass in Taiwan.

This species is found in southern Taiwan, and it seems to be of limited occurrence.

Annuals; culms weak, ascending and rooting at lower nodes. Ligule membranous, about 7 mm long, ciliated; leaves amplexicaudal, cordate at base. Inflorescence of weak 3-9 digitate racemes; rachis 2/3 as long as the spikelet; pedicelled spikelet reduced to a 0.5 mm long pedicel. Sessile spikelets lanceolate, about 3.8 mm long, compressed; lower glume coriaceous, papillate, 5-7-nerved, the nerves hispidulous, as long as the spikelet; upper glume papery, margins membranous, 1-nerved, as long as the lower glume; lower lemma lanceolate, palea wanting; upper floret awned, about 2.5 mm long, lemma hyaline, bifid at the apex, awn about 0.7 mm long, arising from near the base; palea hyaline, about 2 mm long. Caryopsis slender, about 1.8 mm long.

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.

Culms decumbent, branching from nearly every node, lower nodes rooting. Blade ovate-lanceolate, amplexicaul, acute; liguie small, ciliate; sheath hairy along margin, usually shorter than the intemode. Inflorescence of 2 to several digitately arranged spike-like racemes; rachis many-noded, ciliate, easily falling off at each node. Spikelets dimorphic, paired, the one pedicellate and the other sessile; pedicellate spikelet reduced to a mere pedicel. Sessile spikelet laterally compressed, basal part with white haris; lower glume covered with tubercled bristles, the bristles shorter on the lower part and longer on the upper part; upper glume acute, margins membranous, hard on dorsal part, lower lemma shorter than the lower glume, membranous, nerves obscure, epaleate; upper lemma transparent, convex, awned; from the very base, awn geniculate.

Distributed in the Caucasus, India, China and Japan.

Distributed in India, Malaysia and China.

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].

Nepal, India, Taiwan, Malaysia.

700-1500 m

Streamsides, damp meadows, among crops, other moist places; 100–2300 m.

Phalaris hispida Thunb., FL Jap. 44, 1784.
Arthraxon hispidus Makino subsp. ciliaris (Beauv.) Masamune & Yamamoto in Trans. Nat. Hist Soc. Form, 31: 326. 1941.

Alectoridia quariniana A. Rich., Tent. Fl. Abyss. 2: 448. pl. 99. 1851.
Arthraxon okamotoi Ohwi, Act. Phytotax. Geobot. 11: 165. 1942; Koyama, Grass. Jap. Neighb. Reg. 444. 1987.

Arthraxon quartinianus (A. Rich.) Nash
Alectoridia Quariiniana A. Rich. Tent. Fl. Abyss. 2 : 448. 1852. Arthraxon ciliaris Quartinianus Hack, in DC. Monog, Phan. 6 : 356. 1889.
Stems slender, barbed at the nodes, otherwise glabrous, finally decumbent at the base and rooting at the nodes, the upright portions up to 3 dm. long; leaf-sheaths glabrous or papillose-pilose; blades 2-5 cm. long and 1 cm. wide or less, ovate-lanceolate, acuminate, cordate and clasping at the base, more or less pilose on both surfaces; spikes few to many, 2-3 cm. long, the internodes pilose with long erect hairs; spikelets 3-5 mm. long, the first scale usually hispid toward the apex.
Type locality : Near Adowa, Abyssinia.
Distribution : Introduced into Jamaica and Guadeloupe. Native of Africa and Asia.

Annuals, Terrestrial, not aquatic, Stem s trailing, spreading or prostrate, Stems scandent, climbing, tips pendulous, Stems nodes swollen or brittle, Stems geniculate, decumbent, or lax, sometimes rooting at nodes, Stems mat or turf forming, Stems terete, round in cross section, or polygonal, Stems branching above base or distally at nodes, Stem nodes bearded or hairy, Stem internodes solid or spongy, Stem internodes hollow, Stems with inflorescence less than 1 m tall, Stems, culms, or scapes exceeding basal leaves, Leaves mostly cauline, Leaves conspicuously 2-ranked, distichous, Leaves sheathing at base, Leaf sheath mostly open, or loose, Leaf sheath hairy, hispid or prickly, Leaf sheath and blade differentiated, Leaf blades lanceolate, Leaf blades ovate, Leaf blades 2-10 mm wide, Leaf blades 1-2 cm wide, Leaf blades mostly flat, Leaf blades more or less hairy, Ligule present, Ligule a fringed, ciliate, or lobed membrane, Ligule a fringe of hairs, Inflorescence terminal, Inflorescence lateral or axillary, Inflo rescence solitary, with 1 spike, fascicle, glomerule, head, or cluster per stem or culm, Inflorescence a panicle with narrowly racemose or spicate branches, Inflorescence a panicle with digitately arranged spicate branches, Inflorescence with 2-10 branches, Inflorescence branches more than 10 to numerous, Inflorescence branches paired or digitate at a single node, Flowers bisexual, Flowers unisexual, Spikelets pedicellate, Spikelets sessile or subsessile, Spikelet less than 3 mm wide, Spikelets with 2 florets, Spikelets paired at rachis nodes, Spikelets in paired units, 1 sessile, 1 pedicellate, Spikelets bisexual, Spikelets unisexual, Spikelets disarticulating below the glumes, Glumes present, empty bracts, Glumes 2 clearly present, Glumes equal or subequal, Glumes equal to or longer than adjacent lemma, Glumes 1 nerved, Glumes 3 nerved, Lemmas thin, chartaceous, hyaline, cartilaginous, or membranous, Lemma coriaceous, firmer or thicker in texture than the glumes, Lemma 1 n erved, Lemma 3 nerved, Lemma glabrous, Lemma apex acute or acuminate, Lemma distinctly awned, more than 2-3 mm, Lemma with 1 awn, Lemma awn less than 1 cm long, Lemma awn 1-2 cm long, Lemma awn subapical or dorsal, Lemma awns straight or curved to base, Lemma awn twisted, spirally coiled at base, like a corkscrew, Lemma margins thin, lying flat, Lemma straight, Stamens 2, Styles 2-fid, deeply 2-branched, Stigmas 2, Fruit - caryopsis, Caryopsis ellipsoid, longitudinally grooved, hilum long-linear.

Arthraxon hispidus, is a grass commonly known as small carpetgrass or hairy jointgrass. It is native to East Asia and was accidentally introduced to the United States, where it is considered an invasive species.