Lemnaceae Martinov

Scientific Description

Common name. Duckweed Family.

Habit and leaf form. Much reduced, aquatic herbs. Plants of very peculiar form; thalloid (thallus small to minute, globular, flat or linear, with or without raphides). Leaves absent. Plants with roots, or rootless. Annual. Hydrophytic; free floating. Stem anatomy. Secondary thickening absent.

Reproductive type, pollination. Fertile flowers functionally male and functionally female, or functionally male, or functionally female. Unisexual flowers present. Plants monoecious (usually), or dioecious (rarely).

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’ (in groups of 2—3). Inflorescences spatheate, or espatheate. Flowers minute. Perianth absent. Fertile stamens present, or absent (in female flowers). Androecium 1. Androecium exclusively of fertile stamens. Stamens 1. Anthers dehiscing transversely, or dehiscing via pores to dehiscing via longitudinal slits (sometimes dehiscing apically via pores or short slits); bisporangiate (Wolffia), or tetrasporangiate (Lemna). Fertile gynoecium present, or absent (in male flowers). Gynoecium ostensibly 1 carpelled; ostensibly monomerous (imaginatively interpretable as pseudomonomerous?); 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 1—4-seeded utricle. Seeds endospermic, or non-endospermic. Endosperm oily, or not oily. Seeds with starch. Embryo weakly differentiated to well differentiated (sometimes lacking a radicle). Cotyledons 1. Embryo straight. 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. World distribution: cosmopolitan. X = 5, 8, 10, 11, 21. 30 species.