Rhizomatous glabrous monoecious or rarely dioecious herbs with tubers, usually growing submerged in fresh water or (after drying up) on wet soil. Leaves all basal and alternate, simple and usually with long petioles; blades oblong to linear. Inflorescence usually a simple or bifid spike (rarely the spike digitate and divided into 3–4 parts), at first enclosed in a thin caducous spathe, very rarely (in the South African species A. ranunculiflorus) the inflorescence is much abbreviated simulating a Ranunculus flower. Flowers bisexual or more rarely unisexual. Tepals 1–6 or absent, petal-like, often persisting in fruit. Stamens 1–6, rarely more; filaments free, filiform or flattened; anthers extrorse, 2-thecous, most often only 0.2–0.5 mm. long. Ovaries 3–8, free or slightly united near their base; each ovary superior and 1-locular, with 1–14 erect ovules borne along one side of the locule-wall or at the base of the locule. Fruit a 1–14-seeded follicle. Seeds discoidal to fusiform, straight or slightly curved, with a simple or double testa; endosperm absent.
Fresh-water aquatic herbs with submerged or floating leaves; rhizome tuberous, with fibrous roots. Leaves long-petiolate, or sessile, oblong-elliptic to linear, with few principal parallel nerves and numerous transverse secondary nerves. Flowers hermaphrodite or rarely unisexual, spicate-scapose, spike simple or usually 2- (rarely up to 8-) forked, without bracts. Perianth-segments 1-3, or absent, sometimes petaloid and bract-like, equal or unequal, usually persistent. Stamens 6 or more, free, hypogynous, persistent; anthers extrorse, 2-locular. Carpels free, 3-6, sessile; style short; ovules 2 or more, ascending. Fruits opening on the adaxial side. Seeds without endosperm.
Perennial water plants with a rootstock or rhizome. Leaves in a rosette, submerged and/or floating, very seldom emergent. Inflorescence on a long scape emerging above the water surface, in bud enveloped by a caducous or (rarely) persistent spathe, and composed of 1 or 2-15 spikes. Plants usually monoecious, seldom dioecious or apogamous. Flowers hypogynous, sessile, more or less spirally arranged on the inflorescence axis, or secund. Tepals (1-)2-6, absent in female specimens of dioecious species. Stamens usually 6, absent in female specimens of dioecious species and often in apomictic specimens. Anthers 2-thecate, 4-sporangiate, with extrorse longitudinal dehiscence. Pollen probably always yellow. Carpels usually 3, free, sessile, I-locular, pear-shaped, narrowed into the stylulus with a stigmatic ridge on the ventral side, rudimentary and sterile in male specimens of dioecious specimens, and sometimes more numerous in apomictic specimens. Ovules 2-12 per ovary, basal or marginal. Fruit a follicle with a mostly distinct, lateral or terminal, often curved beak. Seeds without endosperm.
Only one genus of about 45 spp., confined to the Old World, predominantly the southern hemisphere.
The 45 species of the single genus are confined to the Old World, except Europe and temperate Asia. The centre of diversity is in the tropical and subtropical areas ofAfrica and Madagascar. Aponogeton reaches the Cape region of Africa and occurs also in India and Australia. All species have fairly restricted ranges. On the whole, the species do not seem to be endangered, but A. bullosus from the Atherton Tableland (Australia) has become very rare through overcollection for aquarium purposes.
About a dozen species are of some economic importance. In some regions of the world the tubers and in others the leaves are eaten. In Africa the inflorescences of A. distaehyos are used as an ingredient in soups and stews; the plant is cultivated for this purpose. During the flowering season the inflorescences are sold, and they are then even canned.
About five spp. from Sri Lanka and Madagascar are imported on a large scale to Europe and the United States for aquarium purposes. A few other species are imported only occasionally.
A. distachyos is a popular plant for ponds. When there is no ice on the water it may even flower in midwinter.
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