Alismataceae Vent.

Hermaphrodite, monoecious, polygamous or very rarely dioecious (Burnatia, not in Australia), annual or perennial, emergent aquatic herbs, glabrous or subglabrous, tufted, rhizomatous or stoloniferous, with corms, stolons (Luromium, not in Australia) and tubers (Sagittaria); laticifers present. Leaves alternate, spiral or 2-ranked, usually ± basal, simple, sessile or petiolate, mature leaves usually with a petiole and well-developed blade; blade entire, the primary veins parallel, linked by finer transverse secondary veins forming a reticulate pattern; petiole with sheathing base, rounded or triangular in cross-section, with or without transverse septa, often longer than the blade; small scales present at the node inside the leaf sheath; stipules absent. Leaves often dimorphic, the juvenile leaves linear to narrowly elliptic (often not differentiated into petiole and blade), usually submerged. Inflorescence scapose, erect and emergent or floating, usually paniculate or umbel-like, branches or flowers often whorled, or flowers sometimes solitary, bracteate. Flowers actinomorphic, 3-merous, bisexual or unisexual (and then plants often monoecious, very rarely plants dioecious), or with unisexual and bisexual flowers on the same plant (and then plants polygamous). Sepals 3, free, imbricate, green, persistent, sometimes with latex tubes. Petals 3, free, imbricate, ± crumpled in bud, usually white or pink, sometimes yellow (Hydrocleys), caducous. Stamens 3 (Wiesneria, not in Australia) or 6–12 or numerous; filaments free; anthers tetrasporangiate, dithecal, basifixed or versatile, dehiscing by longitudinal slits; staminodes sometimes present (usually present in Hydrocleys). Gynoecium of 3–numerous carpels, carpels free or basally united or joined centrally along shortest side (Damasonium), in 1–several whorl/s or apparently spirally arranged. Ovary superior, 1-locular; style 1, central terminal or basilateral; stigma linear, often decurrent. Ovules 1–numerous per locule, placentation basal, laminar (Butomopsis, Hydrocleys, Limnocharis) or occasionally parietal. Nectaries borne at the base of carpels, stamens or perianth parts. Fruit an aggregate of indehiscent achenes (achenes sometimes glandular as in Sagittaria and in Limnophyton (not in Australia), sometimes with lateral air-canals as in Limnophyton, sometimes with a dorsal wing as in Sagittaria), or dehiscent follicles or thin-walled nutlets. Seeds 1–numerous, smooth, reticulate, costate (Limnocharis), papillate (Butomopsis) or glandular-pubescent (Hydrocleys); endosperm lacking; embryo curved or folded.

Wetland habitats, including swamps, ponds, waterways.

Several species are edible, including the rhizomes and corms of a number of Sagittaria species. Sagittaria sagittifolia (Arrowhead) is cultivated in east Asia for its edible corms. The roots of Sagittaria latifolia (Broadleaf Arrowhead) were eaten by the native Americans (Haynes et al. 1998). The leaves and the scapes of Limnocharis flava (Yellow Velvetleaf) are eaten as a vegetable in tropical Asia (Ogle et al. 2001). Several species of Echinodorus (Amazon Sword, Burhead) and Helanthium are used as aquarium plants. Alisma, Hydrocleys and Sagittaria are also grown as pond ornamentals.