Notocactus scopa), the silver ball cactus, is a species of flowering plant in the cactus family Cactaceae, native to upland southern Brazil and Uruguay.

It is a ball- or cylinder-shaped cactus growing to 5–50 cm (2–20 in) tall by 10 cm (4 in) broad, with a spiny, woolly crown and pale yellow flowers in summer.

[1] The specific epithet scopa means "broom" and refers to the long spines.

[2] In cultivation it requires a minimum temperature of 10 °C (50 °F), therefore in temperate regions it must be grown under glass or as a houseplant.

scopa has gained the Royal Horticultural Society's Award of Garden Merit.