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This small family of sea-grasses is found in warm, shallow tropical and subtropical coastal waters almost throughout the tropics. The Australian species are found wherever there are calm coasts except along the west and north coasts from Shark Bay to the Gulf of Carpentaria.

Characteristic features of the family Cymodoceaceae in Australia include:

  • submerged sea-grasses from coasts and estuaries
  • leaves flat, linear, several-veined with a sheathing base and small flap (ligule) at the junction of the blade and sheath.
  • flowers small, unisexual, inconspicuous, borne in the axil of a leaf or terminal; male flowers comprising 1 or 2 naked anthers releasing thread-like pollen; female flowers comprising one or more naked ovaries often with spoon-shaped styles
  • fruit a small, dry or fleshy nut


Perennial marine aquatic herbs rooted in the substrate, with their leaves all or mostly submerged. Perennating by rhizomes. Internal secretions not obvious. Plants glabrous. Leaves distichous, both basal and cauline, sessile. Stipule-like lobes present or apparently absent. Lamina simple, symmetric, filiform, acicular, subulate or linear; margins entire, ±flat; venation parallel, with the midrib conspicuous or rarely inconspicuous, and the tertiary venation reticulate; surfaces not punctate; herbaceous. Leaf ligule present. Male and female flowers occurring on the same plant or on separate plants. Inflorescences terminal or axillary, consisting of spikes or solitary flowers. Bracts and bracteoles present. Pollination by water. Flowers odourless; sessile or rarely stalked. Floral disc absent; nectaries absent. Perianth absent. Fertile stamens 2, distinct from each other, ±equal. Staminal filaments absent. Anthers basifixed, not versatile, opening outwards by longitudinal slits, 2 or 4-celled, with apical appendages. Carpel 1, free, with 1 locule. Style terminal, branching from the base. Ovule 1, sessile; placentation apical. Fruit a dry, indehiscent nut. Disseminule macro-surface featureless or awned; micro-surface ±smooth, brown or black, dull. Seeds 1 per fruit. Aril absent. Cotyledons 1. Embryo straight.
(Note: this description has been generated from the coded data compiled for the key. Any errors in the key data will be reflected in the descriptions.)

A treatment of the family Cymodoceaceae has not yet been published in the Flora of Australia. It will appear in Volume 39.

Australian genera of Cymodoceaceae (as recognised for the Flora of Australia)


Amphibolis antarctica (plant and seedling)
Photo: S.Jacobs S.Jacobs 

Cymodocea serrulata (habit)
Photo: S.Jacobs S.Jacobs