Frailea asteroides “obscura”

A trade form of Frailea castanea (formerly Frailea asterioides) sold as 'obscura'; it is not a validly described variety. The species ranges from southern Brazil (Rio Grande do Sul) to northern Uruguay and north-eastern Argentina on rocky outcrops in pampa grassland; it has a flattened, chestnut-brown body no more than 4–5 cm across with tiny black spines pressed downwards. Like most Fraileas, its flowers often set seed without ever opening (cleistogamy).