From the Greek gymnos, naked, kalyx, bud; the flower buds having no covering (Cactaceae). Greenhouse cacti, mostly single-stemmed but a few species making offsets. All have shallow ribs with a ‘chin’ below the areole, and the majority are not heavily spined. Theare large for the size of plant. Flower colours are variable, pink or white occurring on normally red or yellow flowered species.
G. andreae, flattened globular, fine spines, flowers yellow, Argentina. G. bodenbenderianum, flattish growth, brownish-green, young spines almost black, flowers white, pink flushed. Argentina. G. bruchii, smallest of the gymnocalyciums, freely clustering, very weak spines, flowers white, Argentina. G. damsii. broad ribs, dark red markings below chins, flowers white, North Paraguay.
A potting compost with few added nutrients plus a sixth part of sharp sand, grit and broken brick. Keep the plants on a sunny shelf in the greenhouse, water from March to September, gradually decrease in October, then keep dry all winter.
Temperatures should be 65-75 °F (18-24°C) during the growing period, 40-45 °F (4-7°C) in winter. Propagation is by seed sown in pans of a good seed compost in early spring. Keep moist and shaded in a temperature of 70 °F (21°C). Offsets may be rooted from species which develop them.