Habit and leaf form. Aquatic herbs. Annual, or perennial. Leaves basal, or cauline. Plants with a basal concentration of leaves, or with neither basal nor terminal concentrations of leaves; stoloniferous. Hydrophytic; non-marine; rooted. Leaves submerged. Not heterophyllous. Leaves small to very large; alternate (to subopposite); spiral, or distichous; ‘herbaceous’; sessile; sheathing (slightly). Leaf sheaths with free margins. Leaves simple; epulvinate. Leaf blades entire; narrowly linear; 1–7 -nerved; one-veined, or parallel-veined; cross-venulate, or without cross-venules. Leaves with stipules, or without stipules. Axillary scales present (2–10, not fringed). Leaf blade margins serrate (serrulate). Leaves with a persistent basal meristem, and basipetal development. Stem anatomy. Secondary thickening absent.
Reproductive type, pollination. Fertile flowers functionally male, or functionally female. Unisexual flowers present. Plants dioecious. Female flowers solitary, or aggregated in ‘inflorescences’ (reaching water surface by elongation of the peduncle); with staminodes, or without staminodes. Male flowers aggregated in ‘inflorescences’ (numerous flowers on an elongate axis enclosed within the spathe, each flower released as a spherical bud and floating to the water surface where it opens). Floral nectaries absent. Pollinated by water.
Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’. The terminal inflorescence unit (when flowers clustered) cymose. Inflorescences scapiflorous, or not scapiflorous; axillary; spatheate (the spathe around the male inflorescence comprised of 2 bracts, valvate in bud, separating in flower, recurved at apex, not ribbed). Flowers bracteate (forming the ‘spathe’ around the female flower when solitary); minute; regular, or somewhat irregular (outer perianth segments unequal, 2 reflexed and forming buoyant floats and the other erect). The floral asymmetry involving the perianth. Flowers 3 merous; partially acyclic. The gynoecium acyclic. Perigone tube absent. Perianth with distinct calyx and corolla, or of ‘tepals’ (if the minute segments are not determined with separate calyx and corolla); 2–3 (apparently), or 4–6 (technically); 2 -whorled, or 1 -whorled (by misinterpretation); isomerous, or anisomerous; in female flowers white to pink. Calyx if identified as such, 2–3; 1 -whorled; polysepalous; regular. Corolla if identified as such, 1, or 3; 1 -whorled; polypetalous. Fertile stamens present, or absent (female flowers). Androecium 3. Androecial members free of the perianth; free of one another, or coherent; 1 -whorled. Androecium including staminodes. Staminodes 1. Stamens 2. Anthers dehiscing via short slits; extrorse; unilocular to four locular; bisporangiate. Pollen shed in aggregates, or shed as single grains. Fertile gynoecium present, or absent (male flowers). Gynoecium 3 carpelled. The pistil 1 celled (with 3 often obscure placentae). Gynoecium syncarpous; synovarious to synstylovarious; inferior. Ovary unilocular; 1 locular. Styles 3; free, or partially joined; forked; apical. Stigmas 6; dry type; papillate; Group II type. Placentation laminar-dispersed, or basal, or parietal. Ovules in the single cavity 12–100 (i.e. ‘many’); pendulous to ascending; non-arillate; orthotropous, or hemianatropous to anatropous.
Fruit and seed features. Fruit fleshy; indehiscent; capsular-indehiscent (2–3-winged, drawn below the water surface by a spiralling of the peduncle). Dispersal by water. Fruit many-seeded. Seeds endospermic, or non-endospermic; conspicuously hairy, or not conspicuously hairy; with starch. Cotyledons 1. Embryo straight. Seedling. Hypocotyl internode present. Mesocotyl absent. Seedling collar not conspicuous. Cotyledon hyperphyll elongated; assimilatory; dorsiventrally flattened. Coleoptile absent. Seedling macropodous. Seedling cataphylls absent. First leaf dorsiventral. Primary root ephemeral.
Geography, cytology, number of species. Native of Australia. Not endemic to Australia. Australian states and territories: Western Australia, South Australia, Northern Territory, Queensland, New South Wales, Victoria, Australian Capital Territory, and Tasmania. Northern Botanical Province, Eremaean Botanical Province, and South-West Botanical Province.
Additional characters Perianth of male flowers of ‘tepals’, or with distinct calyx and corolla (technically); 3 (apparently), or 4 (includes 1 minute inner perianth segment). Perianth of female flowers of ‘tepals’, or with distinct calyx and corolla (technically); 2–3 (apparently), or 5–6 (includes 3 minute inner perianth segments).
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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/