20. Eleocharis geniculata (Linnaeus) Roemer & Schultes, Syst. Veg. 2: 150. 1817.
黑籽荸荠 hei zi bi qi
Scirpus geniculatus Linnaeus, Sp. Pl. 1: 48. 1753; Eleocharis capitata R. Brown; E. caribaea (Rottbøll) S. F. Blake; S. caribaeus Rottbøll.
Annuals. Rhizomes and stolons absent. Culms tufted to densely tufted, 3-45 cm tall, ca. 0.5 mm thick, soft, with a few longitudinal ribs and sulcate. Leaf sheaths 2, basally reddish and apically straw-colored, 1-1.5 cm, mouth obliquely truncate, apex acuminate. Spikelet globose to ovoid, 3-5 × 3-3.5 mm, densely many flowered, apex obtuse. Basal 3 or 4 glumes empty; basal 2 glumes opposite, amplexicaul for ca. 1/2 of spikelet base; fertile glumes pale rust-colored becoming ± pale, broadly elliptic, 1.6-2 × 1-1.2 mm, midvein obscure, margin narrowly hyaline, apex rounded. Perianth bristles 6-8, rust-colored, slightly shorter than nutlet, laxly and shortly retrorsely spinulose. Stigmas 2. Nutlet dark purple, broadly obovoid to globose-ovoid, 0.7-1.1 × ca. 0.6 mm, biconvex, smooth and shiny; persistent style base pale, depressed conic, 1/5-1/4 as long and 1/7-1/4 as wide as nutlet, slightly reflexed basally on both sides. Fl. and fr. Jan-Apr. 2n = 30.
Shallow water margins at trail edges, sandy coastal habitats; near sea level. Fujian, Guangdong, Hainan, Taiwan [Afghanistan, Bangladesh, India, Indonesia, Japan (Ryukyu Islands), Malaysia, Myanmar, Pakistan, Philippines, Sri Lanka, Thailand; Africa, SW Asia, Australia, Central, North, and South America, S Europe, Madagascar, Pacific islands].