Erect or floating aquatic herbs. 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). Perianth hypogynous, petaloid, divided into 6 lobes more or less arranged in two series, united at the base or free. Stamens 1, 3, or 6, equal or unequal, inserted on the perianth; filaments free; anthers dithecous, opening by longitudinal slits or rarely by terminal pores. 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. Seeds longitudinally ribbed, with copious endosperm.
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. 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. Ovary superior, 3-locular, with axile placentas or 1-locular with 3 parietal placentas; style entire or shortly lobed. Ovules numerous to solitary and then pendulous. Fruit a capsule opening by 3 valves, or indehiscent. Seeds ribbed, with copious endosperm.
Submerged, floating or emergent, freshwater annuals or perennials. Stems of two kinds, vegetative and flowering; vegetative stems indeterminate, with many leaves, with or without sympodial rhizomes or stolons; flowering stems determinate, leafless, bearing a spathe and a terminal inflorescence. Leaves distichous or spiro-distichous, pseudo-whorled in Hydrothrix (see below), often scalelike on rhizomes and stolons, cauline or basal, usually sheathed at the base; stipules axillary or median, either large and enveloping the stem, forming an ochrea, or reduced to a small sheath or ligule or absent; juvenile leaves simple and linear; adult leaves either simple and linear or clearly differentiated into petiole and blade; petioles of variable length, sometimes inflated; blades simple, submerged, floating or emergent, glabrous, linear to orbicular or sagittate, with entire margin, venation acrodromous. Inflorescence terminal, a panicle, umbel-like, a spike, or flowers paired or solitary, subtended by 2 opposed spathes (bracts), one often leaflike, the other sheathing or both leaflike or sheathing; peduncles glabrous or glandular pubescent. Flowers bisexual, zygomorphic or almost actinomorphic, some triheterostylous. Tepals usually 6, sometimes reduced to 4 or 3, equal or unequal, all petaloid, usually withering early, free almost to the base or united basally into a tube, white, blue, pink mottled with yellow or yellow. Stamens all alike or dimorphic, 6, 4, 3 or 1; filaments inserted on the perianth, similar or dissimilar, elongate or swollen, straight or twisted, glabrous or hairy; the hairs linear and smooth, glandular, or moniliform; anthers similar or dissimilar, 2-thecate, basifixed or auriculate and thus appearing dorsifixed, dehiscing introrsely by longitudinal slits or through apical pores, remaining straight or coiling, yellow, blue, brown or black. Gynoecium of 3 united carpels; ovary superior, 3-10cular, sometimes only 1 locule fertile; placentation axile or appearing parietal with intrusive placentas, ovules anatropous, crassinucellar, bitegmic, solitary or numerous; style single, simple and elongate, glabrous or hairy; stigma relatively small, entire or 3-1obed, Dry. Welldeveloped septal nectaries present in Eichhornia and Pontederia. Fruit a capsule or a I-seeded nutlet enclosed in a specialized perianth base (anthocarp). Seeds numerous or solitary, ovoid, usually with longitudinal ribs; endosperm starchy; embryo central, cylindrical, linear; cotyledon terminal; plumule lateral.
A family comprising 9 genera and ± 33 species; distributed mostly in the tropics but extending into temperate zones as well; almost cosmopolitan through introduction. The centre of diversity is tropical and subtropical New World.
All species of Pontederiaceae are aquatic, either obligate submerged plants with emergent flowers of free-floating or bottom-rooted emergents. They are found in a wide range of oligotrophic to eutrophic freshwater habitats. Annual species are restricted to seasonally wet sites, the perennials usually occur in permanent water. Some species of Monoehoria may occur in saline or brackish habitats. Many species are gregarious and may dominate large areas.
Monoehoria (Asia and Africa) and Seholleropsis (Africa) are native to the Old World; Pontederia, Reussia, Eurystemon, Hydrothrix and Zosterella are indigenous to the New World. Eiehhornia and Heteranthera are mostly New World with E. natans and H. eallifolia in Africa. Eiehhornia erassipes, Monoehoria vaginalis, Pontederia eordata and three species of Heteranthera are widely naturalised outside their native range.
Eiehhornia erassipes (water hyacinth) is one of the most troublesome weeds in the world (GopaI1987). In some regions it is being replaced by even more noxious aquatics such as Hydrilla vertieillata and Salvinia molesta. Attempts are being made to utilise E. erassipes as animal feed, mulch, compost, paper fibre or as a source of biogas, alcohol and numerous chemicals, and also for pollution abatement. In some regions such as SE Asia it is used for fodder, fish food and compost and is even regarded as desirable. Ash from burning large quantities of Eiehhornia (probably E. azurea) which contains much K20, is used as a substitute for common salt by the Indians of the Amazon lowland (K. Kubitzki, pers. comm.).
Some species of Heteranthera are pernicious weeds in rice fields. They are difficult to eradicate chemically because they are sensitive to the same chemicals as rice. The seeds remain viable for at least 4 years even when dried or exposed to frost (Schiele 1988). Many species, such as water hyacinth and Pontederia spp., are widely cultivated as ornamentals. Some species of Heteranthera, Zosterella, Hydrothrix and Eiehhornia are grown as aquarium plants. Monoehoria is used in medicine in India and particularly against asthma and toothache; the leaves are eaten by humans in SE Asia.
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