Opuntia megarrhiza Rose is a species of plant in the Cactaceae family. It is endemic to the State of San Luís Potosí in northeastern Mexico. It is known only from 5 populations, around the summits of La Trinidad and Álvarez Mountain Ranges, in San Luis Potosí, northeastern Mexico. Its natural habitat is subtropical or tropical dry lowland grassland. It is an endangered species, threatened by habitat loss, grazing, and harvest for traditional medicinal uses.