Wolffia Schleid.

Scientific Description

Family Lemnaceae.

Habit and leaf form. Much reduced, floating aquatic herbs. Plants of very peculiar form; thalloid (thallus solitary or 2 remaining connected; symmetric, thick, more or less globular, ellipsoid or ovoid, the greatest part of the thallus submerged, green; veins not visible; budding pouch lateral (actually basal), 1 per thallus). Leaves absent. Plants 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 (inflorescence solitary, of 1 male and 2 female flowers, breaking through the upper surface of the thallus).

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’. Inflorescences espatheate. Flowers minute (the smallest flowering plants in the world). Perianth absent. Fertile stamens present, or absent (in female flowers). Androecium 1. Androecium exclusively of fertile stamens. Stamens 1. Anthers dehiscing along an apical line; bisporangiate. Fertile gynoecium present, or absent (in male flowers). Gynoecium ostensibly 1 carpelled; ostensibly monomerous; ostensibly of one carpel; superior. Carpel 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, not winged. Fruit 1 seeded. Seeds endospermic, or non-endospermic; with starch. Embryo weakly differentiated to well differentiated. Cotyledons 1. Embryo straight. Testa smooth. 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.

Additional characters Thallus scaleless.