Calothamnus planifolius is a plant in the myrtle family, Myrtaceae and is endemic to the south-west of Western Australia.

It is an erect shrub with many branches, growing to a height of about 1.5 metres (4.9 ft) with flat leaves and red flowers from September to November.

)[4] The species was first formally described by Johann Lehmmann in 1842 in Delectus Seminum quae in Horto Hamburgensium botanico e collectione.

[5] Calothamnus planifolius occurs in the Avon Wheatbelt and Jarrah Forest biogeographic regions[2] where it grows in gravelly clay over laterite.

[6] It is classified as "not threatened" by the Western Australian Government Department of Parks and Wildlife.