Lemna L.

Scientific Description

Family Lemnaceae.

Habit and leaf form. Much reduced, aquatic herbs. Plants of very peculiar form; thalloid (floating at or sometimes below water surface, solitary or thalli connected to form groups of 2–10 (or more) plants; thallus symmetric or slightly asymmetric, circular, broadly ovate to elliptic, oblong or obovate, flat to biconvex, green, translucent or opaque; veins 1–5; budding pouches 2, lateral, rarely dorsal or ventral to margin). Leaves absent. Plants with roots (root solitary), or rootless. Annual. Hydrophytic; free floating. Stem anatomy. Secondary thickening absent.

Reproductive type, pollination. Fertile flowers functionally male and functionally female. Unisexual flowers present. Plants monoecious. The unisexual flowers not conspicuously in separate aggregates (1 female and 2 male flowers together, borne in one of the budding pouches).

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’. Inflorescences spatheate (spathe reduced, membranous). Flowers minute. Perianth absent. Fertile stamens present, or absent (in female flowers). Androecium 1. Androecium exclusively of fertile stamens. Stamens 1. Anthers dehiscing transversely; bilocular; tetrasporangiate. Fertile gynoecium present, or absent (in male flowers). Gynoecium ostensibly 1 carpelled; ostensibly monomerous; ostensibly of one carpel; superior. Carpel apically stigmatic (stigma concave); 1–7 ovuled. Placentation basal. Ovules ascending; orthotropous, or anatropous, or hemianatropous.

Fruit and seed features. Fruit non-fleshy. The fruiting carpel indehiscent; a utricle, sometimes laterally winged towards top. Fruit 1–5 seeded. Seeds endospermic, or non-endospermic; with starch. Embryo weakly differentiated to well differentiated. Cotyledons 1. Embryo straight. Testa longitudinally ribbed. Seedling. Mesocotyl absent. Seedling collar not conspicuous. Coleoptile absent. Seedling cataphylls absent. Primary root ephemeral.

Physiology, biochemistry. Photosynthetic pathway: C₃.

Geography, cytology, number of species. Native of Australia. Not endemic to Australia. Australian states and territories: Western Australia, South Australia, Northern Territory, Queensland, New South Wales, Victoria, Australian Capital Territory, and Tasmania. Northern Botanical Province and South-West Botanical Province.

Additional characters Thallus scaleless.