Description

Key Characters:

Growth Form: Plants completely submerged.

Stems: Stems slender, slightly compressed and inconspicuously winged, 2–10 dm long, many branched, arising from a dense mat of slender rhizomes.

Roots: Fibrous root system.

Leaves: Leaves simple. Alternate, occasionally the upper ones subopposite. Blades linear, 10–100 mm long, (0.3–)1–1.5(–2.5) mm wide, (1–)3–5–nerved. Apex acute to cuspidate. Base attenuate, attached directly at the node. Surfaces glabrous. Sheathing. Stipules connate into a tubular sheath, the sheath 5–15 mm long, rupturing and deciduous, with portions persistent.

Flowers: Flowers few in subglobose to subcapitate spikes 1–5 mm long, peduncles stout, 3–15(–20) mm long. Flowers small, wind–pollinated, bisexual (perfect), actinomorphic. Perianth of 4 tepals in 1 series, greenish, 0.5–1 mm long. Stamens 4 in 1 series, opposite the tepals, adnate to the claw; anthers subsessile, dithecal, opening by longitudinal slits, extrorse. Pollen spheric. Ovary superior, carpels 4, distinct, alternate with the stamens; ovule 1, attached to the ventral margin of the carpel usually toward the base, orthotropous, usually becoming campylotropous or anatropous after fertilization; style short, terminal, or absent; stigma dry, not papillose.

Fruit: Fruit obliquely obovoid; 1.5–2(–2.5) mm long; dorsal keel prominent undulate–dentate; the 2 lateral keels obscure; style persistent; 0.1–0.4 mm long. Seeds without endosperm.

Ploidy: 2n = 14; 26; 28

Habitat: Aquatic; occurring in streams; taro paddies; and man–made watercourses such as irrigation ditches.

Elevation Range: 0–190 m.