Eragrostis japonica (Thunb.) Trin.

Nile region and Sinai.

Tropical Africa to southeast Asia.

Sandy and heavy soils.

Annual or perennial.

An extremely polymorphic species with three main sources of variation;

1. Palea-keels: smooth palea-keels are confined to South and tropical Africa (Eragrostis namaquensis Schrad.)- scaberulous keels are found throughout tropical Africa (Eragrostis diplachnoides) and Asia.

2. Spikelet size: plants with few-flowered spikelets and lemmas less than 1 mm are generally separated as Eragrostis japonica sensu stricto, although similar forms from Africa with smooth palea-keels are called Eragrostis namaquensis, and those with rough keels are called Eragrostis diplachnoides.

3. Panicle-form: three main sorts can be recognised; interrupted with branches in pseudo whorls (Eragrostis koenigii), almost exclusively Asian; partly whorled but more generally open, branches branched from the base (Eragrostis diarrhena, Eragrostis namaquensis and Eragrostis japonica); branches solitary, bare at the base, panicle open (Eragrostis diplachnoides).

Spikelet and lemma size and panicle form are continuously variable with complete intergradation between the extremes; the two sorts of variation work wholly independently of one another. Furthermore the two forms of palea-keel show no correlation with either of the other two variables. In view of this it is quite impracticable to subdivide the Asian species until some Comprehensive biosystematic study has been undertaken. In the meantime, therefore, all Asian species and varieties, however unsatisfactory this may seem, are reduced to synonymy.

Eragrostis japonica belongs to a small group of closely allied species with membranous ligules which have been treated as a separate genus Diandrochloa De Winter. Judgement on this issue has been deferred until variation within the genus as a whole has been more closely studied.

This species is eaten by cattle when other food is not available. It is considered to be a good fodder for buffaloes in parts of India and Pakistan.

Poa japonica Thunb., F1. Jap. 51. 1784. Culm erect. Blade 15-20 cm long by 2 mm wide; ligule about 0.5 mm long, fimbriate at the apex, pubescent on the back. Inflorescence an elongated open panicle, about 35 cm long. Spikelets several-flowered, about 1.5 mm long. Florets articulating from top downward; glumes chartaceous, ovate-lanceolate, 1-nerved; the lower somewhat smaller than the upper, about 0.6 mm long; lemma chartaceous, about 0.7 mm long, distinctly 3-nerved, basal part inrolled; palea as long as the lemma, 2-keeled, scabrous along keels. Caryopsis about 0.4 mm long; circular in cross-section, embryo 1/2 the length of the caryopsis.

Annual. Culms erect, or geniculate at base, 30–100 cm tall, 1.5–2.5 mm in diam., 3–4-noded. Leaf sheaths usually loose, longer than internodes, glabrous; ligules scarious, ca. 0.5 mm, fimbriate at apex, pubescent on back; leaf blades flat, 3–25 × 0.3–0.5 cm, smooth and glabrous. Panicle elongated, 6–34 × 1.5–6 cm; branches slender, clustered or verticillate, glabrous in axils. Spikelets usually purplish at maturity, ovate, 1–2 mm, 4–8-flowered; rachilla distarticulating between florets from top downward at maturity. Glumes chartaceous, ovate-lanceolate, subequal, 0.6–0.8 mm, 1-veined, apex obtuse. Lemmas chartaceous, broadly elliptical, distinctly 3-veined, apex obtuse, lower lemma ca. 1 mm. Palea subequal to lemma, along 2 keels ciliolate. Stamens 2; anthers ca. 0.2 mm. Caryopsis red-brown, ovoid, 0.4–0.5 mm. Fl. and fr. Jun–Nov.

Tufted annual or short-lived perennial; culms 10-150 cm high, erect. Leaf-blades flat, up to 30 cm long and 5 mm wide; ligule membranous, 0.3-0.6 mm long, truncate, fimbriate. Panicle linear, 4-50 cm long; branches ascending close to the main axis or spreading and the panicle lanceolate to narrowly ovate or branches contracted in dense remote pseudo-whorls, typically 3-14 cm long, bare towards the base, the spikelets shortly pedicelled and appressed to the secondary branchlets or longer pedicelled and spreading. Spikelets 4-14-flowered, ovate-oblong, 1.3-3 mm long, breaking up from the apex, the rhachilla fragile; glumes narrowly ovate to broadly oblong-elliptic, subequal, 0.4-0.7 mm long, acute to obtuse; lemmas broadly ovate, 0.7-1 mm long, obtuse; anthers 2, 0.2 mm long. Caryopsis ellipsoid, 0.3-0.5 mm long.

Tropical Asia, Nepal, China, Japan, Malaysia.

Distributed in India, China, and Korea to Japan and extending to Australia and Africa.

Distribution: Pakistan (Sind, Baluchistan, Punjab, N.W.F.P. & Kashmir); through-out South and Southeast Asia to tropical and South Africa and Australasia.

700-1700 m

Fl. & Fr. Per.: August-October or December.

Fields, roadsides, stream banks. Anhui, Fujian, Guangdong, Guangxi, Guizhou, Henan, Hubei, Jiangsu, Jiangxi, Taiwan, Yunnan, Zhejiang [Bhutan, India, Indonesia, Japan, Malaysia, Myanmar, Nepal, New Guinea, Philippines, Thailand, Vietnam].

Poa japonica Thunberg in Murray, Syst. Veg., ed. 14, 114. 1784.

japonica: of Japan

Robust tufted annual, up to 1.5 m.

Frequent

Annuals, Terrestrial, not aquatic, Stems nodes swollen or brittle, Stems erect or ascending, Stems caespitose, tufted, or clustered, Stems terete, round in cross section, or polygonal, 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 basal, below middle of stem, Leaves mostly cauline, Leaves sheathing at base, Leaf sheath mostly open, or loose, Leaf sheath smooth, glabrous, Leaf sheath hairy at summit, throat, or collar, Leaf sheath and blade differentiated, Leaf blades linear, Leaf blades very narrow or filiform, less than 2 mm wide, Leaf blades 2-10 mm wide, Leaf blade s mostly flat, Leaf blades mostly glabrous, Ligule present, Ligule a fringe of hairs, Inflorescence terminal, Inflorescence an open panicle, openly paniculate, branches spreading, Inflorescence solitary, with 1 spike, fascicle, glomerule, head, or cluster per stem or culm, Inflorescence branches more than 10 to numerous, Flowers bisexual, Spikelets pedicellate, Spikelets laterally compressed, Spikelet less than 3 mm wide, Spikelets with 3-7 florets, Spikelets solitary at rachis nodes, Spikelets all alike and fertille, Spikelets bisexual, Spikelets disarticulating above the glumes, glumes persistent, Spikelets disarticulating beneath or between the florets, Rachilla or pedicel glabrous, Glumes present, empty bracts, Glumes 2 clearly present, Glumes equal or subequal, Glumes distinctly unequal, Glumes shorter than adjacent lemma, Glumes 1 nerved, Lemmas thin, chartaceous, hyaline, cartilaginous, or membranous, Lemma similar in texture to glumes, Lemma 3 nerved, Lemma glabrous, Lemma apex truncate, rounded, or obtuse, Lemma awnless, Lemma margins thin, lying flat, Lemma straight, Palea present, well developed, Palea membranous, hyaline, Palea shorter than lemma, Palea 2 nerved or 2 keeled, Palea keels winged, scabrous, or ciliate, Stamens 3, Styles 2-fid, deeply 2-branched, Stigmas 2, Fruit - caryopsis, Caryopsis ellipsoid, longitudinally grooved, hilum long-linear.

Cỏ lông công hay còn gọi tinh thảo Nhật Bản (danh pháp khoa học: Eragrostis japonica) là một loài thực vật có hoa trong họ Hòa thảo. Loài này được (Thunb.) Trin. mô tả khoa học đầu tiên năm 1830.

乱草（学名：Eragrostis japonica），又名日本鲫鱼草、碎米知风草，是禾本科画眉草属的植物。分布于印度、台湾岛以及中国大陆的云南、江西、湖北、安徽、浙江、广东等地，生长于海拔100米至2,000米的地区，多生在河边、田野路旁或潮湿地，目前尚未由人工引种栽培。