Description :

• Aquatic, herbaceous perennials, occasionally annuals, with deciduous stems forming colonies in fresh or brackish water, either submerged, except for spikes, which are exserted during anthesis, or in some species, leaf blades floating
• Roots in a circle around nodes of rhizome, rooted in substrate
• Rhizomes usually well developed, sympodial, persistent, rarely 0, or plants perennating by formation of winterbuds ('turions')
• Stems elongate, flexible, submerged or floating, or stoloniferous and creeping
• Leaves submerged and/or floating, alternate and/or opposite, simple, entire, often heteromorphic, parallel-veined; floating leaves broad, ovate and petiolate; submerged leaves capillary to lanceolate or elliptic, usually with a well-developed, convolute or tubular, stipular sheath
• Inflorescence pedunculate spikes, with two flowers in Ruppia and several in Potamogeton, exserted, surrounded by a basal sheath
• Flowers bisexual, regular, ebracteate, small, usually wind-pollinated
• Perianth of (2-)4 bract-like, broad, fleshy appendages arising opposite each stamen, sometimes considered as an appendage of the stamens
• Stamens 4, extrorse, arising from claws of segments; anthers 2-thecous, sessile, with longitudinal slits
• Ovary superior; carpels (3)4(-8), free, unilocular; ovule solitary, campylotropous or anatropous at maturity
• Fruit an achene or drupe, usually floating (pericarp aerenchymatous)
• Seeds : hypocotyl well developed; endosperm 0
• x = 13 (7, 12) (aneuploids, high polyploidy)

Nomenclature:

• Potamogeton L.
  • Linnaeus: 126 (1753)
  • Bennett: 45 (1897) under Naiadaceae
  • Obermeyer: 60 (1966)
  • Dahlgren et al.: 315 (1985)
  • Cook: 202 (1990)

Distribution & Notes:

• Global : Species ± 90
• Southern Africa : Species 7: Potamogeton pectinatus L. and P. pusillus L. throughout, remaining species more common in the summer-rainfall area