2. Hydrilla Rich., Mem. Cl. Sci. Math. Inst. Natl. France 12(2): 9 (1814).
Taxon Description
Perennial, submerged herbs. Roots filiform from bottom nodes. Stems long, branched. Leaves submerged, sessile in whorls of 3–8, pale green, translucent, variable in shapes, linear to lanceolate, 1–1.5 X 0.2–0.5 mm, apex apiculate, margin serrulate, midrib distinct, two minute fringed scales at base. Stipules fringed with orange brown hair. Plants dioecious or monoecious Spathes green, ca. 2 mm; male spathes subsessile, consisting of two united bracts, solitary in leaf axils; female spathes sessile, consisting of two united bracts, solitary or rarely two in leaf axils, ribbed. Flowers actinomorphic, borne singly in leaf axils. Male flowers subsessile, membranous, subglobose, with apical knob and corona of setae, 1-flowered; shortly pedicellate, free from spathe on water surface at anthesis. Sepals 3, ovate or obovate, convex. Petals 3, narrower than sepals. Stamens 3. Female flowers sessile, tubular, bifid at apex, 1-flowered. Sepals 3, narrowly oblanceolate. Petals 3, narrower, transparent. Ovary cylindric, 1-celled, enclosed within spathe, extended into a filiform beak; ovules few; styles 3. Fruit cylindric or linear, ca. 7 mm. Seeds brown, fusiform, borne in a single linear sequence, rarely more than 5, ca. 2.5 mm, smooth.
Taxon Statistics
Worldwide one species, in temperate to tropical regions.
1. Hydrilla verticillata (L.f.) Royle, Ill. Bot. Himal. Mts.: t. 376 (1839).
Serpicula verticillata L.f., Suppl. Pl.: 416 (1782); Vallisneria verticillata (L.f.) Roxb.
Perennial submerged herbs, 20–50 cm. Roots filiform from bottom nodes, turions present. Stems long, branched. Leaves sessile in whorls of 3–8, pale green, translucent, variable in shapes, linear to lanceolate, 1–1.5 X 0.2–0.5 mm, apex apiculate, margin serrulate, midrib distinct, two minute fringed scales at base. Plants dioecious or monoecious. Flowers actinomorphic, unisexual, borne singly in leaf axils. Male spathes subsessile, female spathes sessile, ribbed. Sepals 1.5-3 mm long, ovate or obovate, convex. Petals narrower than sepals. Stamens with minute filaments, filaments oblique, anthers erect, 4-loculed, explosively dehiscent. Female flowers tubular, sessile, apex bifid, 1-flowered. Sepals and petals similar to male ones. Ovary cylindric, 1-celled, enclosed within spathe, extended into a filiform beak; ovules few, styles 3. Fruit cylindric or linear, ca. 7 mm. Seeds brown, fusiform, borne in a single linear sequence, rarely more than 5, ca. 2.5 mm, smooth.
Distribution: Nepal, W Himalaya, E Himalaya, Tibetan Plateau, Assam-Burma, S Asia, E Asia, SE Asia, C Asia, SW Asia; Europe, Africa and Australasia.
Altitudinal range: 100–1600 m.
Ecology: Ponds and running water.
Flowering: May─July. Fruiting: August─October.
Whole plants used as medicine (Pal and Nimse, 2006).
Description of female flowers and fruit characters of Hydrilla verticillata is based on the other review articles (Cook, C.D.K. and Lfsnd, R., 1982. A revision of the genus Hydrilla (Hydrocharitaceae). Aquat. Bot., 13: 485–504.), floras (Qingfeng et al. 2010) protologue text, and digital image of holotype [LINN-1106.1].