Habit and leaf form. Erect aquatic herbs; laticiferous. Perennial, or annual (rarely); plants with a basal concentration of leaves; rhizomatous, or rhizomatous and tuberous. Hydrophytic; rooted. Leaves submerged, or emergent, or floating. Heterophyllous (usually, the submerged leaves differing from emergent leaves), or not heterophyllous (when all leaves either submerged or emergent). Leaves alternate; petiolate, or sessile; sheathing; simple. Leaf blades linear, or ovate; parallel-veined; cross-venulate, or without cross-venules; sagittate, or rounded at the base. Axillary scales present. Leaf anatomy. Hairs present (hairs sparse), or absent. Stem anatomy. Secondary thickening absent.
Reproductive type, pollination. Fertile flowers functionally male and functionally female, or functionally male, or functionally female. Unisexual flowers present. Plants monoecious, or dioecious (rarely). The unisexual flowers aggregated in different parts of the same inflorescence (the flowers staminate above and carpellate below). Floral nectaries present. Nectar secretion from the gynoecium, or from the androecium.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’. The terminal inflorescence unit cymose, or racemose. Inflorescences scapiflorous; paniculate, racemose, or rarely umbelliform, of 1–17 whorls, the whorls with 2–3 flowers; with involucral bracts, or without involucral bracts. Flowers bracteate; regular; 3 merous; cyclic. Floral receptacle developing a gynophore. Perigone tube absent. Perianth with distinct calyx and corolla; 6; 2 -whorled; isomerous; without spots, or spotted; different in the two whorls; white, or pink to purple (inner), or green (outer). Calyx 3; 1 -whorled; polysepalous. Corolla 3; polypetalous; white, or pink to purple (rarely). Fertile stamens present, or absent (when female). Androecium 7–100 (i.e. to many). Androecial members branched (seemingly spiralled, but actually reflecting whorls of trunk bundles). Androecial sequence determinable, or not determinable. Androecial members when in more than one whorl, maturing centripetally; free of the perianth; free of one another; 1–20 -whorled (i.e., to ‘many’ whorls). Androecium exclusively of fertile stamens. Stamens 7–100 (i.e. to ‘many’); triplostemonous to polystemonous; alterniperianthial. Filaments hairy, or glabrous; linear to dilated. Anthers linear to orbicular; basifixed; dehiscing via longitudinal slits; extrorse. Fertile gynoecium present, or absent (male flowers). Gynoecium 20–100 carpelled (or more — i.e. to many, spirally arranged); apocarpous; eu-apocarpous; superior. Carpel apically stigmatic; 1 ovuled. Placentation basal. Stigmas dry type; papillate; Group II type. Ovules ascending; anatropous, or amphitropous.
Fruit and seed features. Fruit non-fleshy; not spinose (usually), or spinose (then spines less than 2 mm long); an aggregate. The fruiting carpels not coalescing. The fruiting carpel indehiscent; an achene (compressed, numerous, often laterally winged, ecostate, glandular, with a conspicuous dorsal wing). Seeds non-endospermic; with starch. Cotyledons 1. Embryo strongly curved (horseshoe-shaped). Seedling. Hypocotyl internode present. Mesocotyl absent. Seedling collar not conspicuous. Cotyledon hyperphyll elongated; assimilatory; more or less circular in t.s. Coleoptile absent. Seedling macropodous. Seedling cataphylls absent. First leaf dorsiventral. Primary root ephemeral.
Physiology, biochemistry. Photosynthetic pathway: C3.
Additional characters Fruit rostrate.
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Western Australian Herbarium (1998–). FloraBase—the Western Australian Flora. Department of Biodiversity, Conservation and Attractions. https://florabase.dpaw.wa.gov.au/