Heteranthera rotundifolia Griseb.

Plants annual. Vegetative stems submersed with elongate inter-nodes, or if emersed at early age, then procumbent. Flowering stems 2–12 cm, distal internode 1–6 cm. Sessile leaves submersed, forming basal rosette; blade linear to oblanceolate, thickened, 2.4–5 cm × 2–4 mm. Petiolate leaves floating or emersed; stipule 1–5 cm; petiole 3–11 cm; blade round to oblong, 1–5 cm × 5–25 mm, length equaling (or, on young plants, greater than) width, base cordate to truncate, apex obtuse. Inflorescences 1-flowered; spathes 1–2.8 mm, glabrous. Flowers opening within 1 hour after dawn, wilting by midday; perianth blue or white, salverform, tube 11–29 mm, limbs essentially actinomorphic, lobes narrowly elliptic, 5.2–18.2 mm, proximal lobe longer, distal central lobe with lateral flanges toward base; stamens unequal, lateral stamens 2.8–8 mm, central stamen 3.9–8.5 mm; filaments linear, curved downward apically, glandular-pubescent; style glabrous. Seeds 8–15-winged, 0.5–1 × 0.3–0.6 mm. 2n = 14.