Pontederia limosa Swartz, Prodr., 57. 1788; Leptanthus ovalis Michaux

Plants annual. Vegetative stems submersed with elongate inter-nodes only on plants in over 5 cm of water, or emersed and short. Flowering stems 2–24 cm, distal internode 1–11 cm. Sessile leaves forming basal rosette, blade linear to oblanceolate, thin or sometimes thickened, 3.1–6 cm × 3–5 mm. Petiolate leaves emersed; stipule 1–6 cm; petiole 2–13 cm; blade oblong to ovate, 1–5 cm × 4–33 mm, length equaling or greater than width; base truncate to cuneate, apex acute. Inflorescences 1-flowered; spathes 0.9–4.5 cm, glabrous. Flowers opening within 1 hour after dawn, wilting by midday; perianth blue or white, salverform, tube 15–44 mm, limbs essentially actinomorphic, lobes equal, narrowly elliptic, 5.2–26.3 mm, distal lobes yellow toward base; stamens unequal, lateral stamens 2.3–7.8 mm, central stamen 3.3–7.2 mm; filaments linear, glandular-pubescent; style glabrous. Seeds 9–14-winged, 0.5–0.8 × 0.2–0.6 mm. 2n = 14.

Flowering May--Nov. Shallow water or emersed at pond edges and in roadside ditches; 0--2000 m; Ariz., Ark., Calif., Colo., Fla., Ill., Iowa, Kans., Ky., La., Miss., Mo., Nebr., N.Mex., Okla., S.Dak., Tenn., Tex.; Mexico; West Indies; Central America; South America (Argentina, Bolivia, Brazil, Colombia, Ecuador, Paraguay, Venezuela).

Personal observation of Heteranthera limosa suggests that it is best adapted for growth in water less than 5 cm deep and is a poor competitor with the closely related H. rotundifolia in deeper waters.