Echinocereus rigidissimus, commonly known as the Arizona Rainbow Cactus or Rainbow Hedgehog Cactus is a solitary, growing cactus, that rarely branches or offsets with age. Echinocereus rigidissimus grows to a height of up to 30 cm, and a width of 11 cm when mature, with pectinate radial spines curved slightly towards the stem, the new spines are initially reddish to magenta and fades to a yellow or light pink colour when they mature. Echinocereus rigidissimus, flowers in flushes throughout the spring season, with multiple buds borne atop the plant from younger areoles, the flowers are bright pink in colour with a white coloured throat. If pollination is successful, Echinocereus rigidissimus forms circular shaped, greenish to dark purplish fruit, with white flesh and dark brown to black seeds approximately 3 months after flowering. Since it rarely offsets, Echinocereus rigidissimus is propagated by seed.