A. myriostigma is a spineless cactus defined by the presence of three to seven (usually five) pronounced vertical ribs which define the cactus' shape when young (the genus name "astrophytum", literally, "star plant", is derived from the resulting star-like shape). As the cactus ages, more ribs may be added and it becomes more cylindrical in shape, growing up to about 70-100 cm tall and 10-20 cm in diameter. The stem is often covered with whitish flecks.
The cactus flowers in the spring or summer with one or more waxy flowers 4-6 cm diameter near its apex; the numerous petals are yellow, sometimes with an orange or red base. Pollinated flowers develop into a hairy reddish fruit about 2-2.5 cm in diameter. Plants may take up to six years to flower. A. myriostigma is commonly grown as an ornamental plant in cactus collections.