Habit and leaf form. Herbs. Plants with a basal concentration of leaves. Hydrophytic; rooted. Leaves floating (usually, sometimes semi-erect); alternate; spiral; petiolate; sheathing; gland-dotted (on undersurface, usually), or not gland-dotted; simple. Leaf blades dorsiventral; entire; ovate to orbicular; pinnately veined, or palmately veined; cross-venulate; shallowly to deeply cordate. Leaves without stipules. Leaf blade margins entire, or crenate, or dentate. Leaves without a persistent basal meristem. Leaf anatomy. Hydathodes present. Stem anatomy. Nodes tri-lacunar, or penta-lacunar. Secondary thickening absent, or developing from a conventional cambial ring.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Plants commonly heterostylous (or tristylous), or homostylous. Entomophilous.
Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’; either clustered close to a leaf blade on a petiole-like stem or else in pairs along distinct stems. The terminal inflorescence unit cymose, or racemose. Inflorescences scapiflorous, or not scapiflorous. Flowers long- pedicellate (and held above water level); small to medium-sized; regular; 5(–8) merous; cyclic; tetracyclic. Free hypanthium absent. Hypogynous disk present; intrastaminal. Perianth with distinct calyx and corolla; 10(–16); 2 -whorled; isomerous. Calyx 5(–8); 1 -whorled; polysepalous, or gamosepalous; regular. Corolla 5(–8); 1 -whorled; gamopetalous (with a tube); valvate (or induplicate-valvate); regular; hairy adaxially (the tube usually with clusters of hairs or papillae midway along its length, each cluster positioned on the prolongation of the midline of a corolla lobe); yellow to orange, or white and yellow, or pink to purple. Corolla members variously fringed. Androecium 5(–8). Androecial members adnate (to the tube); free of one another. Stamens 5(–8); isomerous with the perianth; oppositisepalous (the filaments alternating with the C lobes). Anthers versatile; dehiscing via longitudinal slits; introrse; tetrasporangiate. Gynoecium 2 carpelled. The pistil 1 celled. Carpels reduced in number relative to the perianth. Gynoecium syncarpous; synstylovarious; superior, or partly inferior. Ovary unilocular; 1 locular. Gynoecium median. Ovary with 5 basal glands. Gynoecium stylate. Styles 1; apical. Stigmas 2–5; wet type; papillate; Group III type. Placentation parietal (with 2–5 placentas). Ovules in the single cavity 10–100 (‘many’); horizontal; anatropous.
Fruit and seed features. Fruit fleshy, or non-fleshy; dehiscent, or indehiscent; a capsule (with apical valves on stranded plants), or capsular-indehiscent (and ripening underwater on recurved pedicels). Capsules when dehiscent, splitting irregularly. Fruit 10–100 seeded (i.e. ‘numerous’). Seeds endospermic. Endosperm oily. Seeds arillate (often), or non-arillate. Cotyledons 2. Embryo straight. Testa smooth, or with tubercles.
Geography, cytology, number of species. Native of Australia. Not endemic to Australia.
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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/