Common name. Manatee-grass Family.
Family Sometimes included in Zanichelliaceae.
Habit and leaf form. Herbs. Perennial; plants with neither basal nor terminal concentrations of leaves (herbaceous and monopodial, or woody and sympodial); rhizomatous. Hydrophytic; marine; rooted. Leaves submerged; alternate, or opposite (or apparently so); when alternate, spiral, or distichous; sessile; sheathing. 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. 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. Pollinated by water.
Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’; in cymes. The terminal inflorescence unit (when flowers aggregated) cymose. Flowers small. Perianth absent. Fertile stamens present, or absent (female plants). Androecium in male flowers 2. Androecial members coherent (the two dorsally united, the anthers paired on a common filament). 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. Ovules pendulous; non-arillate; orthotropous.
Fruit and seed features. Fruit fleshy, or non-fleshy (exocarp hard or fleshy, sometimes enclosed in a fleshy bract); an aggregate. The fruiting carpel indehiscent; nucular. Seeds non-endospermic. Cotyledons 1.
Geography, cytology, number of species. World distribution: warm seas. X = 7. 16 species.