Mammillaria microhelia aka Biznaguita

Mammillaria microhelia is a small, perennial cactus from Mexico. It belongs to the cactus family, Cactaceae. Kew gives its range as Guanajuato to Hidalgo. LLIFLE places it more narrowly in central Querétaro. There, it grows among volcanic rocks in semi-desert and oak woods. LLIFLE reports it as endangered, with grazing and illegal collecting threatening wild plants.

Plants grow as single columns or form clumps. The green stems reach about 0.5 feet (0.15 m) tall. Some reach 0.8 feet (0.25 m) or more. Each stem measures about 0.10–0.16 feet (0.03–0.05 m) across. Larger stems can reach 0.20 feet (0.06 m) across. Blunt, cone-shaped tubercles cover the stems. Their bases may bear a little wool when young. Dense spines spread outward in a spoke-like pattern. Each group has 30–50 pale radial spines. These range from white to yellowish and may curve backward. Most groups also bear one to four stronger central spines. Their reddish-brown or yellow-brown shades contrast with the pale outer spines. Some plants lack central spines; others have more than four.

The flowers open in spring and have a bell shape. Each can reach about 0.05 feet (0.016 m) across. Flower colours include cream, yellow-green, pink and purple. Some tepals carry a darker stripe down the middle. The flowers have white filaments and pale yellow anthers. Short, pale green stigma lobes rise just above the stamens. The fruits are pale green or pale pink. They contain brown seeds.

In cultivation, this cactus needs bright light and free drainage. Use an open cactus mix with at least half grit. Keep peat and other humus-rich ingredients low. Water only after the soil feels dry, then let it drain. Avoid wetting the spines, which can hold water against the plant. Good airflow helps reduce the risk of rot. Root rot is a key problem where moisture lingers. Keep the plant dry through winter. LLIFLE advises frost protection, despite reporting survival at −5°C when dry. A dry winter rest helps flowering and long-term survival.

Its small size suits growing in a small pot. Repot at intervals of two to three years. Grow new plants from seed, or less often from cuttings. Seeds can sprout within one to two weeks at 21–27°C. Keep young seedlings out of full sun and provide airflow.