Fl. Peruv. Prodr., 9, plate 2. 1794.
Herbs, annual or perennial, rooting in mud. Vegetative stems submersed and growing to surface, or emersed and procumbent or short. Flowering stems submersed and growing to water surface, or emersed. Sessile leaves submersed, forming basal rosette, or emersed on elongate stem; blade linear or sometimes oblanceolate, apex acuminate to obtuse. Petiolate leaves floating or emersed; blade reniform, cordate, or oblong, membranous, apex acute to obtuse. Inflorescences spicate or solitary, 1–30-flowered, elongating over 1–several days; spathes folded or clasping, with acute to caudate apex, or rarely expanded leaflike extension. Flowers: individuals open 1 day only; perianth with tepals connate 1/2 or more of its length, yellow, blue-mauve, mauve, or white, tubular or salverform, limb lobes linear to oblanceolate or narrowly elliptic, shorter than 2 cm, apex obtuse to acuminate; stamens 3, unequal, 2 lateral ones usually shorter; filaments yellow or purple, inflated in some species, glabrous, glandular-pubescent, or pilose; anthers yellow or purple, rounded, oblong, or sagittate; ovary incompletely 3-locular; ovules 10–many; style 3-lobed. Fruits capsular, elongate. Seeds 10–200, ovoid, testa with longitudinal wings.
Western Hemisphere, Africa
Species 12 (7 in the flora).
In the flora area, Heteranthera peduncularis Bentham is known only from one collection in Arizona (C. Mohr s.n., US), probably from about 1900. The center of the distribution of this species is in the highlands of Mexico. It is closely related to Heteranthera multiflora and H. reniformis, and may be distinguished by distinctly cordate leaves, mauve perianth limb lobes, and glabrous filaments.
|1||Sessile leaf blade linear; inflorescences 1-flowered; stamens equal; anthers coiling.||Heteranthera dubia|
|1||Sessile leaf blade linear to sometimes oblanceolate, or absent; inflorescences 1–24-flowered; stamens unequal; anthers not coiling.||> 2|
|2||Inflorescences 1-flowered; perianth limbs essentially actinomorphic.||> 3|
|2||Inflorescences 2–24-flowered; perianth limbs zygomorphic.||> 4|
|3||Vegetative stems commonly elongating unless plant emersed from early age; petiolate leaf blade round to oblong, base cordate to truncate; distal central perianth limb lobe with lateral flanges||Heteranthera rotundifolia|
|3||Vegetative stems elongating only on plants in over 5 cm of water; petiolate leaf blade oblong to ovate, base truncate to cuneate; distal central perianth limb lobe without lateral flanges||Heteranthera limosa|
|4||Petiolate leaves not produced; emersed peduncle glandular-pubescent; inflorescences elongating over several days||Heteranthera mexicana|
|4||Petiolate leaves present on mature plants; emersed peduncle glabrous; inflorescences elongating in 1–2 days.||> 5|
|5||Spikes shorter than spathes, terminal flower sometimes extending past spathe apex; filament hairs white; spathes equal to or barely longer than subtending internode of flowering stem.||Heteranthera reniformis|
|5||Spikes longer than spathes, except on cleistogamous inflorescences; filament hairs purple; spathes 3 or more times longer than subtending internode of flowering stem.||Heteranthera multiflora|