Mammillaria hernandezii

Mammillaria hernandezii is a tiny cactus from Oaxaca, Mexico. It belongs to the cactus family, Cactaceae. Its native range lies in the Tehuacan-Cuicatlan Valley. It grows in mountain sites at 7,218–7,546 feet [2,200–2,300 metres]. Plants occupy gaps in oak and pine woods. They also grow among grass on limestone slopes. Their small, broken range faces damage from goat grazing. Both habitat quality and the number of mature plants are declining.

Each plant usually has one round or slightly flattened stem. In cultivation, it may slowly form a clump. Stems usually reach about 0.08 feet [0.025 metres] tall and wide. Cultivated stems can reach 0.15 feet [0.045 metres] across. The soft, dark green stem has no latex. It bears pyramid-shaped tubercles, with short white wool between them. Each spine cluster has 17–25 short radial spines. These white, cream or tan spines curve back toward the stem. They form a somewhat comb-like pattern without crossing one another. The plant has no central spines and has thickened, fleshy roots.

The flowers look large beside the small stem. They reach 0.066 feet [0.02 metres] long and 0.08 feet [0.025 metres] across. Most are cherry red or bright pink-red, with a paler throat. White flowers occur too. Blooms open during daylight and shut at night. In northern Europe and the United States, flowering falls in autumn and winter. Cold, damp weather and low light can hinder flower growth. Sunny October weather can prompt the blooms to open.

The fruit stays inside the stem as it ripens. Botanists call this hidden fruit habit cryptocarpy. The seeds are large and black. They may stay inside for about nine years, sometimes longer. Some escape as the stem swells and its covering splits. Others remain until the old stem breaks down after death. Seeds can then sprout close to the parent plant. Fresh seed may germinate poorly, while older seed can sprout faster. Germination may stretch over several years.

This is a slow-growing cactus that can be hard to maintain. Growers often graft it; grafted plants grow faster and flower freely. Plants on their own roots grow much more slowly. Propagation uses seed, cuttings or grafting. Young seedlings need firm roots before moving into separate pots. In the wild, dry-season shrinkage can pull stems below ground. Flowers may then rise through the soil above the hidden plant. This cycle helps explain why a plant may barely enlarge between years.