Habit and leaf form. Herbs. Perennial; plants with neither basal nor terminal concentrations of leaves; rhizomatous (rhizome creeping, monopodial, herbaceous, with 1 or more simple roots and a short erect stem at each node). Hydrophytic; marine; rooted. Leaves submerged; alternate; distichous (1–4 per stem); sessile; sheathing (with sheath margins incurved so sheath appears a similar width to blade; sheath persistent after blade shed). Leaf sheaths with free margins. Leaves simple; epulvinate. Leaf blades entire; linear; 3 -nerved (but only the midvein conspicuous); parallel-veined. Leaves ligulate (at junction of sheath and blade). Axillary scales present. Leaf blade margins entire but somewhat serrulate or distinctly toothed near apex. 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 subsessile or sessile. Male flowers stalked. Plants not viviparous. Pollinated by water.
Inflorescence and flower features. Flowers solitary (or apparently 1-flowered); terminal (subtended by the terminal leaf, an axillary bud of penultimate leaf developing into a leafy shoot replacing the original axis); 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 different heights). Androecium exclusively of fertile stamens. Stamens 2. Anthers unilocular, or bilocular; tetrasporangiate. 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 simple. Ovules pendulous; non-arillate; orthotropous.
Fruit and seed features. Fruit non-fleshy (pericarp stony); an aggregate. The fruiting carpel indehiscent; nucular (ovoid to almost globular, somewhat compressed). 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 and Eremaean Botanical Province.
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/