Description:

• Marine perennials, monoecious, completely submerged; with creeping, much-branched, compressed, orange-brown rhizomes; with several simple roots with long roothairs at nodes
• Stems, if present, floriferous, annual
• Leaves alternate, distichous, grass-like, parallel-veined, sheathing at base; sheath tubular or convolute, with a small biauriculate ligule; lamina linear, striate, apex rounded, 2-lobed or emarginate, axillary scales 4 or 2
• Inflorescences forming erect annual sympodial branches, each terminating in a 'fertile' leaf, enclosing in its sheath a unilateral spadix on which male and female flowers are arranged alternately in 2 rows, with or without marginal bract-like infolded lobes or 'retinacula' (interpreted by some botanists as a reduced perianth)
• Male flower a solitary, sessile, unilocular, dorsifixed anther; pollen filiform, with same density as seawater, captured by stigmas
• Female flower consisting of a superior, unilocular, 1-ovuled ovary terminating in a short style and 2 long stigmatic branches, protogynous (stigmas protruding from sheath during anthesis); ovule pendulous, orthotropous, bitegmic
• Fruit an indehiscent, or irregularly dehiscent nut, graniform, smooth or longitudinally striped or ribbed
• Seed: endosperm 0
• x = 6 (polyploidy)

Nomenclature:

• Zosteraceae
  • Bennett: 41 (1897) under Naiadaceae
  • Phillips: 53 (1951) under Potamogetonaceae
  • Obermeyer: 57 (1966)
  • Den Hartog: 42 (1970)
  • Cook: 222 (1990)

Distribution & Notes:

• Global: Genera 3, species 18, in marine and brackish water, often forming extensive beds along the coasts of the temperate seas of the northern and southern hemispheres, a few species extend into tropical waters
• Southern Africa: Genus 1, species 1

References:

• BENNETT, A. 1897. Naiadaceae. Flora capensis 7
• COOK, C.D.K. 1990. Aquatic plant book. SPB Academic Publishing, The Hague
• DEN HARTOG, C. 1970. The seagrasses of the world. North-Holland Publishing Company, Amsterdam
• OBERMEYER, A.A. 1966. Zosteraceae. Flora of southern Africa 1
• PHILLIPS, E.P. 1951. The genera of South African flowering plants, edn 2. Memoirs of the Botanical Survey of South Africa No. 25

Resources:

• Zosteraceae genus: Zostera