Cyperus gymnocaulos, commonly known as spiny flatsedge, is a sedge of the family Cyperaceae that is native to Australia.

[1] The rhizomatous perennial grass-like sedge typically grows to a height of 0.35 to 1 metre (1.1 to 3.3 ft) and has a tufted habit.

[1] It normally has a short thick rhizome with smooth, trigonous and terete culms.

[2] The species was first formally described by the botanist Ernst Gottlieb von Steudel in 1854 as part of the work Synopsis Plantarum Glumacearum.

[3] It is found in swamps and along creeks and rivers and other damp areas in all the states of mainland Australia as well as the Northern Territory.