Mammillaria formosa aka Pincushion Cactus

Mammillaria formosa is a small cactus in the Cactaceae family. Its common names include Owl Eyes and Royal Cross. It comes from Mexico, from the northeast south to Michoacán. Wild plants grow on hills and plains in dry shrubland. They often grow beneath bushes among other cacti and succulents. Records place them at 3,150–7,710 feet [960–2,350 metres] above sea level. The species is widespread and abundant in its native range.

Young plants have one round, light green stem. With age, the stem grows taller and takes on a column shape. Its tip has a shallow dip in the centre. Stems reach about 0.16–0.66 feet [0.05–0.20 metres] tall. Each can reach 0.33 feet [0.10 metres] wide or more. The growing head splits in two as the plant ages. Shoots may also form at the base. These branches build a low mound over time. Cultivated clumps can reach 1.64 feet [0.50 metres] across or more after 12–15 years.

Close spirals of crowded, pyramid-shaped tubercles cover the stems. These tubercles contain latex, and the plant has fibrous roots. White wool fills the spaces between tubercles near the flowering area. Young areoles are oval and woolly. Most plants have 20–22 fine white radial spines per areole. Some lack these spines. Four to seven central spines range from pinkish to brown. Their tips are darker than their bases. Spine length and wool cover vary a great deal between plants. The fruits are club-shaped and deep, muted pink-red. Their seeds are light brown.

This cactus is easy to grow as a collection plant. Give it strong light, but avoid light that scorches its stems. Good light helps keep its growth compact. Use a soil mix that drains well. During active growth, water well, then let the mix dry fully. Give little or no water in winter. Its expanding clump may need frequent repotting as more heads form.

Seed is the preferred way to raise new plants. Seeds germinate readily at 20–22°C. Available offsets offer another way to propagate it. Raising several seedlings reveals the wide range of wool cover. This variation, along with its branching shape, gives each mature clump a distinct appearance.