Description:

• Freshwater or marine, perennial or annual herbs, usually monoecious or dioecious, partially or completely submerged
• Roots terrestrial or floating
• Leaves alternate, opposite or in verticils, radical, in rosettes or cauline, submerged or with floating blades, with or without sheathing base, margins sometimes finely dentate
• Flowers unisexual or rarely bisexual, regular to slightly irregular (Vallisneria), submerged in marine genera, in others exserted during anthesis, usually exserted from a pedunculate, or rarely sessile, tubular, bifid spathe, or rarely subtended by 2 free, opposite bracts; pollination in marine genera hydrophilous, in others entomophilous
• Male flowers usually many and, in some genera, becoming detached and free-floating; perianth 1- or 2-seriate, with 3 outer segments often sepaloid, valvate, and 3 inner petaloid, imbricate; stamens (1)3-many in one or more trimerous whorls, inner occasionally staminodial; anthers 2-thecous, opening longitudinally, pollen sphaeroid or, in marine genera, confervoid (united in strings); rudimentary ovary sometimes present
• Female flowers mostly solitary inside the spathe, with an inferior, 1-locular ovary, with 3 or 6, rarely more, parietal placentas at times protruding towards centre; ovules few to many, anatropous or orthotropous, bitegmic; styles as many as placentas; stigmas simple or bifid
• Fruit rounded or tubular, fleshy or leathery, rarely dry and dehiscent, usually rostrate, with persistent style bases
• Seeds few to many, dispersed by dissolution of walls, which become mucilaginous; embryo straight; endosperm 0 or scanty (in Ottelia)

Nomenclature:

• Hydrocharitaceae
  • Wright: 1 (1912)
  • Obermeyer: 100 (1966)
  • Cook: 96 (1990)

Distribution & Notes:

• Global: Genera 17, species 100, cosmopolitan, all aquatic, 3 marine
• Southern Africa: Genera 5 (1 introduced freshwater; 1 marine, 3 freshwater), species 13

References:

• COOK, C.D.K. 1990. Aquatic plant book. SPB Academic Publishing, The Hague
• OBERMEYER, A.A. 1966. Hyrocharitaceae. Flora of southern Africa 1
• WRIGHT, F.C. 1912. Hydrocharideae. Flora capensis 5, 3

Resources:

• Classification of Hydrocharitaceae
• Key to Hydrocharitaceae genera

• Hydrocharitaceae genera: