紫萍Spirodela polyrrhiza (Linn.) Schleid.

别名：水萍;浮萍;紫背浮萍;紫背萍;

科名：浮萍科 Lemnaceae

属名：紫萍属 Spirodela

《中国植物志》第13(2)卷207页
  1．紫萍（本草纲目）水萍（神农本草经），浮瓜叶、氽头蕰草、浮飘草（上海），萍、田萍（福建、甘肃）；水萍草（浙江杭州），浮萍（各地），紫背浮萍 图版42: 1
  Spirodela polyrrhiza (L.) Schleid. in Linnaea 13: 392. 1839; Matsum. et Hayata in Journ. Coll. Sci. Univ. Tokyo 22: 463. 1906; Hand. -Mazt., Symb. Sin. l: 1368. 1936; 裴鉴、单人骅, 华东水生维管束植物 34, 图41. 1952; Ohwi, Fl. Jap. 260. 1956; Backer, Fl. Jav. 3: 127. 1968. ——Lemma polyrrhiza L., Sp. Pl. ed. 1: 970. 1753.
  叶状体扁平，阔倒卵形，长5-8毫米，宽4-6毫米，先端钝圆，表面绿色，背面紫色，具掌状脉5-11条，背面中央生5-11条根，根长3-5厘米，白绿色，根冠尖，脱落；根基附近的一侧囊内形成圆形新芽，萌发后，幼小叶状体渐从囊内浮出，由一细弱的柄与母体相连。花未见，据记载，肉穗花序有2个雄花和1个雌花。
  产南北各地，生于水田、水圹、湖湾、水沟，常与浮萍 Lemna minor 形成覆盖水面的飘浮植物群落。全球各温带及热带地区广布。
  全草入药，发汗、利尿。治感冒发热无汗、斑疹不透、水肿、小便不利、皮肤湿热。也可作猪饲料，鸭也喜食，为放养草鱼的良好饵料。

《Flora of China》 Vol. 23 (2010)
Spirodela polyrhiza  (Linnaeus) Schleiden Linnaea. 13: 392. 1839.
紫萍   zi ping
Lemna polyrhiza Linnaeus, Sp. Pl. 2: 970. 1753.
Fronds obovate to orbicular, 3-10 mm, 1-1.5 × as long as wide, flat, rarely gibbous, sometimes with indistinct papillae on upper surface along veins. Roots (5-)7-21, 1(or 2) perforating scale, 0.5-3 cm. Turions sometimes present, without roots, brownish to olive, orbicular to reniform, 1-2 mm. Ovary with 1 or 2 ovules. Fruit laterally winged toward apex. Seed with 12-20 ribs. Fl. (very rare) Jun-Sep. 2n = 30, 32, 38, 40*, 50, 80.
Ponds, lakesides, rice fields, pools, ditches; not seen in regions with cool summers; sea level to 2900 m. Anhui, Fujian, Guangdong, Guangxi, Guizhou, Hebei, Heilongjiang, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Jilin, Liaoning, Qinghai, Shaanxi, Shandong, Shanxi, Sichuan, Taiwan, Yunnan, Zhejiang [worldwide].
A variety, Spirodela polyrhiza var. masonii Daubs was proposed for the ecotype, which has gibbous fronds. This variety, however, occurs only rarely throughout the whole distribution range, so the use of this name is not systematically necessary.A variety, Spirodela polyrhiza var. masonii Daubs was proposed for the ecotype, which has gibbous fronds. This variety, however, occurs only rarely throughout the whole distribution range, so the use of this name is not systematically necessary.