|Abstract||Mostly annual, rather small, of peculiar habit, often moss-like, gregarious, confined to swift running water in streams and cascades. Tissues with silicium. Roots often thallose, flat, stem sometimes absent. Leaves mostly alternate, sometimes scattered, decussate or distichous, base often provided with a sheath, and sometimes stipulelike appendages, often dentate or divided. Flowers terminal, often in cymose inflor., mostly ♀♂, actinomorphic to zygomorphic. Perianth of 3-5 free or subconnate tepals, if reduced to two small, ovate or linear appendages, the bud is enveloped by an originally closed thin ‘spathella’. Stamens hypogyn, 1-~, often 2 unilateral, frequently monadelphic. Anthers mostly introrse, 2—4-locular, splitting lengthwise. Pollen grains single, or in twos or fours. Ovary superior, ovate to elliptic, mostly 2-, rarely 3-locular with thickened central placenta and thin septa. Ovules ~; styles as many as carpels, free, rarely 1. Capsule septicid (often) ribbed; seeds ~, minute, exalbuminous, epidermis mucilaginous.|
Distr. Principally confined to the tropics throughout the world, not yet recorded from the Pacific islands and the greater part of Australia, northward as far as S. Japan, in Malaysia apparently very rare. The locality closest to Malaysia is isthmian Siam where Dr A. KEITH found Podostemon ?algaeformis BTH. in the nineties.