Habit and leaf form. Herbs. Perennial; plants with neither basal nor terminal concentrations of leaves; rhizomatous (rhizome monopodial, herbaceous, with 1 or more roots and a short erect stem arising at each node). Hydrophytic; marine; rooted. Leaves submerged; alternate; distichous (usually 2–3 per stem); sessile; sheathing (sheath persistent after blade is shed). Leaf sheaths with free margins. Leaves simple; epulvinate. Leaf blades entire; linear (or subulate); parallel-veined. Leaves ligulate (at junction of sheath and blade). Axillary scales present. Leaf blade margins more or less entire. 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 sessile. Male flowers stalked. Plants not viviparous. Pollinated by water.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’. Inflorescence many-flowered. Flowers in cymes. The terminal inflorescence unit cymose. Inflorescences rather loose, each flower enclosed in a reduced leaf or bract. Flowers small. Perianth absent. Fertile stamens present, or absent (female plants). Androecium 2. Androecial members coherent (the two dorsally united, the anthers paired on a common filament, attached at same level). Androecium exclusively of fertile stamens. Stamens 2. Anthers unilocular, or bilocular; tetrasporangiate; unappendaged. Pollen grains lacking exine, and dispersed in the sea as long filaments. Fertile gynoecium present, or absent (male plants). Gynoecium 2 carpelled; apocarpous; eu-apocarpous; superior. Carpel stylate; apically stigmatic; 1 ovuled. Placentation apical. Styles each forked. Ovules pendulous; non-arillate; orthotropous.
Fruit and seed features. Fruit non-fleshy (endocarp stony); an aggregate. The fruiting carpel indehiscent; nucular (4-angled in cross-section, inconspicuously ridged along outer surface). Seeds non-endospermic. Cotyledons 1.
Geography, cytology, number of species. Native of Australia. Not endemic to Australia. Australian states and territories: Western Australia, Northern Territory, and Queensland. Northern Botanical Province, Eremaean Botanical Province, and South-West Botanical Province.
Additional characters Fruit rostrate (beak 2-branched).
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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/