Gahnia trifida, the coastal saw-sedge, is a tussock-forming perennial in the family Cyperaceae, endemic to southern Australia.

A herb, sedge or grass-like, with very rough leaf margins and underside.

This branchlet has a spike-like arrangement of numerous, yellow or brown, clusters of flowerheads.

It is found at Rottnest, an island off the west coast, where it grows near the inland salt lakes.

[1][3] The first description of Gahnia trifida was by Jacques Labillardière in Novae Hollandiae Plantarum Specimen (1805).