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.