Description

Key Characters:

Growth Form: Plants only partly submerged.

Stems: Stems stout, nearly terete (cylindrical), 4–15(–20) dm long, unbranched or branched toward apex, arising from rather stout, spreading rhizomes.

Roots: Fibrous root system.

Leaves: Leaves simple. Alternate. Blades dimorphic, submerged ones thin and flaccid, linear–lanceolate to elliptic–lanceolate, 100–200(–300) mm long, 10–20 (–35) mm wide; floating leaves coriaceous, elliptic to oblong–elliptic, (30–)50–120 mm long, (15–)20–40 mm wide. Apex of submerged plants acute; apex of floating plants obtuse to mucronate. Base submerged: attenuate to base; floating: base cuneate. Surfaces glabrous. Submerged leaves 7–15-veined, floating leaves usually 10–20 veined. Petioles of all leaves directly attached at the node; 20–100(–130) mm long. Stipules distinct, those of submerged leaves delicate and caducous, (30–)40–80 mm long, those of floating leaves slightly wider.

Flowers: Flowers numerous in congested spikes 30–60 mm long, peduncles stout, (30–)50–150 mm long. Flowers small, wind–pollinated, bisexual (perfect), actinomorphic. Perianth of 4 tepals in 1 series. greenish or greenish brown, 1.5–2.5 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; 3.5–4 mm long; dorsal keel sharp and prominent; the 2 lateral keels rounded and less prominent; style persistent; 0.3–0.5 mm long. Seeds without endosperm.

Ploidy: 2n = 52

Habitat: Occurring at low elevations in taro paddies; ditches; and ponds on O'ahu and Maui.

Elevation Range: