Seagrasses

Sea-grasses are marine flowering plants that have adapted to living in the sea. They are vascular plants with roots, stems and leaves and their flowers produce pollen and develop seeds. They have creeping stems as lawn grasses do. They can be roughly classified as:

  • paddle weeds or Halophila
  • wire weeds or Amphibolis
  • ribbon weeds or Posidonia

Seagrasses are often found with algae (true seaweeds) attached to them.

You can read more in Dr Anne Brearley’s article on Seaweeds and seagrasses of the Cottesloe area.

Click on an image for a bigger picture (opens in new window).

 Common nameScientific nameDescription
Paddle WeedHalophila ovalisPaddle weed usually grows in the gaps between meadows of other seagrasses and often colonises bare patches of ocean bed created by storms.
WireweedAmphibolisThe wireweeds are the seagrasses that have wiry, segmented, erect stems and a herringbone pattern of leaves. They form dense meadows on the sandy sea-bed, spreading like couch grass with creeping stems and roots. Sometimes their seedlings are washed up. The seeds germinate on the mother plant, producing a seedling with a “comb-anchor”. After being released, the seedling may become anchored in a sandy place where it can grow roots and become established.
Two species of WireweedAmphibolis antarctica and Amphibolis griffithiiThese two species of wireweeds are similar but it is easy to tell them apart - Amphibolus antarctica has shorter leaf-blades and the sheath that wraps around the base of the leaf-blades does not overlap itself, giving it a split appearance.
Ribbon WeedPosidonia australisNamed after the Greek god of the sea, this strappy seagrass is often abundant on our beaches after a storm, washed up in large piles. With creeping stems and fibrous roots, Posidonia forms dense meadows that consolidate the sea-bed and provide sheltered breeding grounds for fish. The leaves also provide attachment for a variety of epiphytic plants and animals. The photo shows live and dried ribbon weed.
Fibre Ball This is composed of the tangled fibres from the base of the Ribbon Weed Posidonia australis. When these seagrasses decompose, their basal fibres tangle together to form fibre balls.