A. caput-medusae is a rare succulente belonging to the Cactaceae botanical family. The cactus is solitary and the stem is very reduced. The stem is composed of thin cylindrical stem covered with white dots. At the base of the stem there are papyraceous bristles brownish in color. The terminal areoles are circular, white and spiniferous, the others are floriferous. The spines are rigid, whitish and darker at the apex. Blooming occurs in autumn and blossom are borne along the stem. The flowers are large, diurnal, yellow, with the base of the inner perianth segments orange coloured. The fruits are green and fleshy and bear big, cup-like, black seeds.