Laticiferous water plant. Leaves floating, ovate with rounded or emarginate apex, base deeply cordate, basal lobes obtuse, 1.5-6.5 cm long measured along the midrib, greatest width 2.5-10.5 cm; submerged phyllodes sometimes present, linear to lanceolate, shortly petioled, 5-11 by 1/3-1/2 cm; nerves 15-17, prominent on the under-surface, the inner 6-8 directed apically, the others towards the lobes, on the undersurface connected by parallel cross-veins under an angle of c. 70° spaced 1-2 mm, upper surface with veins densely reticulate; petiole ribbed, c. 15-30 cm with air-channels and in sicco prominent septations spaced 2-4 mm; sheath with a broad scarious margin. Peduncles 1-7, rather flaccid, floating, ribbed, with wide air-channels, short-patent hairy towards the apex incl. the raceme 15-40 cm. Racemes c. 1/3 as long as the peduncle, with 2-6 whorls of 2-3 flowers; 1-4 lower whorls with ☿ flowers, the upper ones male. Bracts 3 in each whorl, broad-elliptic, connate, rounded at the top, green with scarious margin, 0.8-2 cm long. Pedicels up to 1 cm, after anthesis thickened and recurved. Sepals broadly triangular-ovate, blunt, keeled, 8-11 by 7-10 mm. Petals obovate to orbicular, very broadly rounded at the apex, delicate, white with sometimes a small purple spot above the yellowish base, 12-15(-18) mm. Stamens in the ☿ flowers 8-12, in an interrupted whorl grouped opposite to the sepals, in the ♂ flowers 6-10, in a whorl, exceeding the rudiments of the pistils, filaments 2-3 mm, much dilated and flattened towards the base, fine-papillose; anthers oblong, 1½ by ¾ mm. Carpels co, elliptic to suborbicular, with a dorsal and a ventral, undulate, membranous crest; style terminal directed inward, c. 1 mm; stigma punctiform. Achenes ∞, 3-4 mm, elliptic, short-stalked, with broad, blunt-spiny crest, spines connected by a thin membrane, c. 1 mm high; lateral ridges without or with minute warts; beak broadly scarious-margined; exocarp with a very fine reticulate relief. Seed brown, 0.5 mm.
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Stolons usually lacking. Floating leaves broadly ovate to cordate-ovate, 1.2-9 × 1-10 cm, base deeply cordate, apex obtuse; submerged leaves linear or lanceolate, 3-11 cm × 5-10 mm. Inflorescences racemose, 8-40 cm, in 2-6 whorls of 3 flowers; bracts connate toward base. Bisexual flowers usually on lower 1-4 whorls; pedicels 1-1.5 cm, thickened. Male flowers with pedicel 2-5 cm. Sepals not reflexed after anthesis, ovate, 0.5-1.5 cm × 3-15 mm. Petals fugacious, obovate, subequal to sepals. Stamens 6 to numerous; anthers yellow. Achenes obovoid or elliptic, 2-4 × 1.5-3 mm, with cristate wing and oblique adaxial beak. Fl. May-Sep, fr. Jun-Nov. 2n = 22*.
Achenes compressed, 2¼-4 by 1¾-3 mm, wings typically deeply crested, rarely nearly smooth, their faces usually prominently 1-ribbed, the rib occasionally remotely echinate, rarely unadorned.
Ditches and wet rice-fields, 10-1000 m, often in great quantity, fl. Jan.-Dec. Flowers are closed in the morning, open at noon or somewhat later but never very widely, and close at dusk.
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