Herbs, annual or perennial, aquatic, rooted in mud or free-floating. Stems of 2 types, vegetative and flowering; vegetative stems indeterminate, bearing many leaves, glabrous; flowering stems determinate, usually emersed, bearing single leaf, spathe, and terminal inflorescence. Leaves of 2 types, sessile and petiolate; stipule marcescent, apex truncate, associated with petiolate leaves only; sessile leaves submersed or rarely emersed, forming basal rosette or alternate on elongate stem, blade linear to occasionally oblanceolate, base sheathing, margins entire; petiolate leaves floating or emersed, blade cordate, reniform, or ovate. Inflorescences paniculate, spicate, umbellate, or 1-flowered; spathes bractlike, folded or clasping, commonly with acute to caudate extension. Flowers sessile, 3-merous; perianth with tepals connate proximally, yellow, blue, mauve, or white, tube tubular or funnelform, limb 6-lobed; stamens 3 or 6, adnate to perianth; pistils 3-locular, 1 or 3 developing to maturity; placentation parietal or basal; ovules 1–many. Fruits capsular or utriculate. Seeds smooth or with longitudinal wings.
Herbs annual or perennial, aquatic, floating or rooting in substrate. Roots fibrous. Vegetative stems short or creeping, thick. Leaves rosulate or distributed along stem, distichous; petiole mostly distinct, sometimes inflated; leaf sheath usually present; leaf blade emersed or submersed, broadly ovate, lanceolate, or broadly linear, sometimes completely reduced, stomata paracytic. Flowering stems erect, solid, terminating in a leaf, spathe, and inflorescence. Inflorescences paniculate, racemose, spicate, umbellate, or 1-flowered, subtended by a spathelike or tubular leaf sheath; bracts minute or absent. Flowers bisexual, mostly actinomorphic, sometimes zygomorphic. Perianth segments 6, in 2 whorls, petaloid, free or basally connate into a tube. Stamens usually 6 in 2 whorls, rarely 3 or 1, inserted on perianth, often unequal or dissimilar; filaments slender, free; anthers 2-loculed, introrse, dehiscing by longitudinal slits or rarely by pores; pollen grains 2- or 3-nucleate, colpi 1 or 2(or 3), distal or subequatorial. Ovary superior, 3-loculed and placentation axile or 1-loculed and placentation parietal; ovules numerous per locule or 1 and pendulous, anatropous. Style 1; stigma capitate or minutely 3-lobed. Fruit a 3-valved capsule or indehiscent. Seeds small, longitudinally ribbed or smooth; endosperm copious, mealy; embryo central in seed, straight, terete.
Ovary superior, 3-locular, with axile placentas or 1-locular with 3 parietal placentas; style entire or shortly lobed
Stamens 6 or 3, rarely 1, inserted on the perianth, sometimes somewhat unequal in length or 1 the longest of all; filaments free; anthers 2-locular, opening lengthwise by slits or rarely by pores
Fruit a capsule opening by 3 valves, or indehiscent
Ovules numerous to solitary and then pendulous
Aquatic erect or floating herbs
Leaves with floating or immersed blades sheathing at the base
Flowers bisexual, actinomorphic, arranged in racemes or panicles subtended by a spathe-like leaf-sheath; bracts minute or absent
Perianth hypogynous, corolline; lobes 6 or 4, sub-biseriate
Seeds ribbed, with copious endosperm
Seeds longitudinally ribbed, with copious endosperm
Leaves with floating and/or emersed blades, sheathing at the base
Flowers hermaphrodite, regular or slightly irregularly two-lipped, arranged in racemes, spikes, panicles or sub-umbellate inflorescences subtended by a spathe-like leaf-sheath or solitary (Eichhornia)
Erect or floating aquatic herbs
Ovary superior, 3-locular with axile placentas or unilocular with 3 parietal placentas; style entire or lobed; ovules anatropous, numerous to solitary
Fruit a capsule opening by 3 valves, or an indehiscent achene
Perianth hypogynous, petaloid, divided into 6 lobes more or less arranged in two series, united at the base or free
Alexander, E. J. 1937. Pontederiaceae. In: N. L. Britton et al., eds. 1905+. North American Flora…. 47+ vols. New York. Vol. 19, pp. 51–60. Barrett, S. C. H. and D. E. Seaman. 1980. The weed flora of California rice fields. Aquatic Bot. 9: 351–376. Eckenwalder, J. E. and S. C. H. Barrett. 1986. Phylogenetic systematics of Pontederiaceae. Syst. Bot. 11: 373–391. Kaul, R. B. and C. N. Horn. 1986. Pontederiaceae. In: Great Plains Flora Association. 1986. Flora of the Great Plains. Lawrence, Kans. Pp. 1239–1241. Rosatti, T. J. 1987. The genera of Pontederiaceae in the southeastern United States. J. Arnold Arbor. 68: 35–71. Solms-Laubach, H. 1883. Pontederiaceae. In: A. L. P. P. de Candolle and C. de Candolle, eds. 1878–1896. Monographiae Phanerogamarum.... 9 vols. Paris. Vol. 4, pp. 501–535.