Mammillaria petterssonii

Mammillaria petterssonii is known as Pettersson's pincushion cactus. It belongs to Cactaceae, the cactus family. Its native range runs from northeastern Mexico to Jalisco. There it grows in desert or dry shrubland. It is a succulent subshrub that forms clumps. In cultivation, it suits pots indoors, conservatories, and greenhouses. It is not native to Britain or Ireland.

The plant has round stems that reach about 0.4 feet (0.12 metres) across. These stems group together to form the clump. The RHS gives a mature height of 0.3–1.6 feet (0.1–0.5 metres). It lists the same range for the plant's spread. Plants reach their mature size in two to five years. Pointed tubercles cover the stems, with wool in their axils. Long central spines have a yellow-brown colour. Fine white radial spines surround these longer spines. The RHS classes the plant as evergreen.

Flowers appear from spring into summer around the stem's crown. They form a ring near the top of each stem. Each flower has a funnel shape and pink or white colouring. Dark pink lines mark the middle of the flower segments. The contrast between pale radial spines and darker central spines adds interest. The rounded stems and rings of flowers suit close viewing in pots. The supplied species account does not describe its fruit. It gives no basis for judging edibility or toxicity.

Grow this cactus under glass in a mix that drains well. The RHS recommends cactus compost and accepts loam or sand. Acid, neutral, and alkaline soil conditions all suit it. Give it strong light, but shield it from hot sun. A sheltered south- or west-facing position matches the RHS guidance. Water well while the plant grows, then reduce watering in winter. Its H2 rating means it tolerates cool conditions but cannot survive freezing. The listed minimum temperature range is 1–5°C.

No pruning is needed, and the RHS reports few disease problems. Mealybugs can attack the plant, including its roots. New plants can be raised from seed or divided offsets. Sow seed in late winter or early spring at 19–24°C. Remove offsets for division in early spring. These methods offer two ways to build a pot collection.