Discocactus diersianus

Discocactus diersianus is a small, solitary cactus, sometimes form clumps if damaged by fire. The cactus has an olive-green to dark green epidermis and a discoid to flattened globose stem, measuring 10 to 13 cm (3.9 to 5.1 in) tall and 25 to 26 cm (9.8 to 10.2 in) in diameter, supported by branched roots. Its stems feature 13 to 18 distinct, vertically or slightly spirally arranged ribs, each with a V-shaped groove below the areoles and divided into rounded tubercles. Oval, sunken areoles, 1 to 1.2 mm (0.039 to 0.047 in) long and 0.7 mm (0.028 in) wide, are situated on these tubercles, with 4 to 6 per rib, and are the origin of the spines. These spines, typically gray to brownish-gray or blackish-gray with dark brown to black tips, are strongly curved or hooked and rounded or quadrangular in cross-section. They consist of a single, sometimes absent, central spine up to 4 cm (1.6 in) long, accompanied by 4 to 10 radial spines ranging from 6 to 8 cm (2.4 to 3.1 in) in length. Adult plants develop a distinctive woolly cephalium at their apex, reaching 9 cm (3.5 in) in height and up to 10 cm (3.9 in) in diameter. …

Plants are typically found in seasonally dry tropical environments at around 650 meters elevation in Tocantins and Goiás, Brazil growing in full sun on exfoliating granite rocks mixed with humus, often alongside bromeliads.