Schoenus quadrangularis is a species of sedge endemic to mountainous of southern South Africa.

Preliminary evidence suggests that the southern African Schoenus have a tendency to form hybrids with each other, which partially explains why they can be difficult to identify.

[1] Schoenus quadrangularis is a species in family Cyperaceae, tribe Schoeneae, a clade that includes other notable genera such as Costularia, Gahnia, Lepidosperma, Oreobolus and Tetraria.

[1] The genus Tetraria once included species from the southern African Schoenus; however, both molecular and morphological evidence suggests that the two genera are evolutionary distinct.

[1] This species has been mostly observed growing in damp sites in the mountains, with elevations ranging from 82-1370 m.[1]