Gymnostoma is a genus of about eighteen species of trees and shrubs, constituting one of the four genera of the plant family Casuarinaceae. The species grow naturally in the tropics, including at high elevations having temperate climates, in forests in the region of the western Pacific Ocean and Malesia. In New Caledonia, published botanical science describes eight species found growing naturally, which botanists have not found anywhere else (endemics). Other species are native to Borneo, Sumatra, Maluku, and New Guinea, and one endemic species each in Fiji and the Wet Tropics of Queensland, Australia.