The families of flowering plants.
Habit and leaf form. Herbs. Perennial; with neither basal nor terminal aggregations of leaves (herbaceous and monopodial, or woody and sympodial); rhizomatous. Hydrophytic; marine; rooted. Leaves submerged. Leaves alternate, or opposite (or apparently so); when alternate, spiral, or distichous; sessile; sheathing. Leaf sheaths with free margins. Leaves simple; epulvinate. Lamina 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.
Leaf anatomy. Hairs absent.
The mesophyll without calcium oxalate crystals. Vessels absent.
Stem anatomy. Secondary thickening absent. Xylem without vessels.
Root anatomy. Root xylem without vessels.
Reproductive type, pollination. Plants dioecious. Pollination by water.
Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; in cymes. The ultimate inflorescence unit (when flowers aggregated) cymose. Flowers small.
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. Pollen grains nonaperturate; 3-celled.
Gynoecium 2 carpelled; apocarpous; eu-apocarpous; superior. Carpel stylate; apically stigmatic; 1 ovuled. Placentation apical. Ovules pendulous; non-arillate; orthotropous; bitegmic.
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. Testa without phytomelan.
Physiology, biochemistry. Proanthocyanidins present.
Geography, cytology. Sub-tropical to tropical. Warm seas. X = 7.
Taxonomy.Subclass Monocotyledonae. Dahlgren et al. Superorder Alismatiflorae; Zosterales. APG 3 core angiosperms; Superorder Lilianae; non-commelinid Monocot; Order Alismatales.
Species 16. Genera 5; Cymodocea, Amphibolis, Halodule, Syringodium.