Echinocereus rigidissimus is a slow-growing cactus species that typically grows in clumps or solitary stems. It has a dark green stem with a cylindrical shape and can grow up to 6 inches (15 cm) in height and 3 inches (7.6 cm) in diameter. The plant has several radial spines that are yellow or white in color, and one central spine that is longer and darker. During the spring, E. rigidissimus produces bright pink or magenta flowers that bloom from the top of the plant.