An order of the class Ginkgoopsida having about 35 species in the genus Ephedra. These plants are mostly of arid regions. They include freely branched, low shrubs with reduced, scalelike leaves and green photosynthetic twigs. The species are dioecious (seldom gynodioecious). The genus is known from Asia to Europe, in northern Africa, in the United States and Mexico, and from Bolivia to Patagonia. It is not known in the fossil record.