Najadaceae Juss.

Scientific Description

Common name. Water-nymph Family.

Habit and leaf form. Aquatic herbs. Annual, or perennial; plants with neither basal nor terminal concentrations of leaves. Hydrophytic; non-marine; rooted. Leaves submerged; (sub-) opposite to whorled, or alternate (‘subopposite or subverticillate’); when in verticils, 3 per whorl; sessile; sheathing (more completely so in the lower members of each sub-pair or verticil). Leaf sheaths not tubular; with free margins. Leaves simple. Leaf blades entire; linear; one-veined; without cross-venules. Leaves somewhat with stipules (at the sides of the sheath), or without stipules. Axillary scales often present (two, small). Leaf blade margins serrate to dentate (usually toothed), or entire. 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, or dioecious. Pollinated by water.

Inflorescence and flower features. Flowers solitary (axillary); with (male) or without (female) a spathelike set of scales and a flask-shaped or two-lipped inner involucre; small. Perigone tube present, or absent (depending on interpretation). Hypogynous disk absent. Perianth of ‘tepals’, or vestigial, or absent (depending on interpretation of the ‘involucre’, which in female flowers is absent or inconspicuous and adnate to the gynoecium); if interpreted as such, sepaloid. Fertile stamens present, or absent (female flowers). Androecium 1. Androecium exclusively of fertile stamens. Stamens 1; with sessile anthers. Anthers dehiscing irregularly; unilocular, or four locular; tetrasporangiate. Pollen shed in aggregates. Fertile gynoecium present, or absent (from male flowers). Gynoecium 1 carpelled; ostensibly monomerous; ostensibly of one carpel; superior. Carpel 1 ovuled. Placentation basal. Ovules ascending; non-arillate; anatropous.

Fruit and seed features. Fruit non-fleshy. The fruiting carpel indehiscent; an achene (pericarp thin). Seeds non-endospermic; with starch. Embryo well differentiated. Cotyledons 1. Embryo chlorophyllous; straight. Seedling. Hypocotyl internode present. Mesocotyl absent. Seedling collar not conspicuous. Cotyledon hyperphyll elongated; assimilatory; more or less circular in t.s. Coleoptile absent. Seedling macropodous. Seedling cataphylls absent. First leaf dorsiventral. Primary root ephemeral.

Physiology, biochemistry. Photosynthetic pathway: C₃.

Geography, cytology, number of species. World distribution: cosmopolitan. X = 6, 7. 50 species.