Parodia scopa aka Silver Ball Cactus

Parodia scopa, commonly known as the silver ball cactus, is a small globose to short-cylindrical cactus in the family Cactaceae, native to upland southern Brazil (Rio Grande do Sul, and adjacent Paraná and Santa Catarina) and Uruguay, where it grows in a subtropical climate. Mature plants typically reach 5–50 cm (2–20 in) in height and around 10 cm (4 in) in width, presenting a densely spined, woolly crown that gives the species its silvery appearance and its species epithet — scopa is Latin for "broom", a reference to the elongated, broom-like spines.

The species was originally described as Cactus scopa Spreng. in 1825 and has been shuffled between genera many times, accumulating a long list of synonyms including Echinocactus scopa, Echinopsis scopa, Cereus scopa, Malacocarpus scopa, and most familiarly Notocactus scopa (under which name it is still widely sold by collectors). It was transferred to Parodia by N.P. Taylor in 1987, and Kew's World Checklist of Vascular Plants now treats Notocactus succineus, Notocactus rudibuenekeri, Notocactus glomeratus, and Parodia succinea, among many others, as heterotypic synonyms of a broadly circumscribed Parodia scopa.

In summer the plant produces pale yellow funnel-shaped flowers at or near the crown, opening in succession over several weeks. As with the rest of the genus, it is monoecious and chasmogamous, and flowers are typically visited by insects.

In cultivation Parodia scopa is treated as a tender cactus: it requires a minimum temperature of 10 °C (50 °F), so in temperate regions it must be grown indoors or under glass. Subspecies P. scopa subsp. scopa has received the Royal Horticultural Society's Award of Garden Merit, reflecting its long history as a reliable collector's and windowsill cactus.

The species is assessed as Vulnerable (VU) on the IUCN Red List (taxon 152861), reflecting habitat decline in its restricted range.