5. Heteranthera rotundifolia (Kunth) Griseb. (mud plantain)

Pl. 189 e, f; Map 768

Plants annual. Vegetative stems creeping, at least some of the leaves at well‑separated nodes. Leaves dimorphic, clustered, the rosette leaves of seedlings linear and lacking a well‑defined blade, the emergent, later leaves long‑petiolate, the blades 1–5 cm long, mostly longer than wide, lanceolate to ovate, truncate to shallowly cordate at base, the tips rounded. Inflorescences produced on specialized flowering stems, these 2–12 cm long, erect to spreading. Flowers single, sessile at the tips of the flowering stems. Perianth purple to white, zygomorphic, 2‑lipped, the tube 11–29 mm long, the lobes linear to narrowly oblong, 5–18 mm long, the middle lower lobe the longest, descending, the 2 lateral lower lobes spreading, the 3 upper lobes erect, the middle upper one with a yellow spot at the base. Stamens unequal, the filaments glandular‑hairy. 2n=14. July–October.

Scattered in the southern half of the state and along the Missouri River (U.S., mostly in the central and southwestern states, south to South America, West Indies). Emergent aquatic, usually in shallow, stagnant or slow‑moving water or along muddy margins, in ponds, lakes, ditches, sloughs, and rice fields.