Caustis dioica is a sedge that is native to Western Australia.
The monoecious and rhizomatous perennial sedge has a tangled, tussocky habit. It typically grows to a height of and a width of and has pungent smelling leaves. The plant blooms between September and December producing yellow-brown flowers.
It is found in the Mid West, Wheatbelt, South West, Great Southern and Goldfields-Esperance regions where it grows in sandy-loamy soils.