Habit and leaf form. Herbs. Perennial; plants with neither basal nor terminal concentrations of leaves; rhizomatous (rhizome monopodial, herbaceous, with 1–5 roots and a short erect stem at each node). Hydrophytic; marine; rooted. Leaves submerged; alternate; distichous (2–7 per stem); sessile; sheathing (with sheath margins incurved so sheath appears a similar width to blade; sheath compressed, persistent after blade shed). Leaf sheaths with free margins. Leaves simple; epulvinate. Leaf blades entire; linear; 7–17 -nerved; parallel-veined. Leaves ligulate (at junction of sheath and blade). Axillary scales present. Leaf blade margins entire but serrulate or minutely spiny at 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 sessile or shortly stalked. Male flowers prominently 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 the same height). Androecium exclusively of fertile stamens. Stamens 2. Anthers unilocular, or bilocular; tetrasporangiate; appendaged. The anther appendages apical (subulate). 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 very deeply forked. Ovules pendulous; non-arillate; orthotropous.
Fruit and seed features. Fruit non-fleshy (pericarp stony); an aggregate. The fruiting carpel indehiscent; nucular (laterally compressed, 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 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/