Mammillaria luethyi

Mammillaria luethyi is a tiny cactus. It comes from northern Coahuila, Mexico. Its family is Cactaceae, the cactus family. Kew lists it as a succulent subshrub. It grows in desert or dry shrubland. Wild plants grow on slabs of limestone. These sites lie in the Chihuahuan semi-desert. LLIFLE records plants about 2,625 feet [800 metres] above sea level.

Plants grow alone or in groups. Much of their growth stays below ground. Their round stems are flat and almost black-green. Wild stems span about 0.05 feet [0.015 metres]. When grown in care, they can span 0.13 feet [0.04 metres]. A fleshy taproot grows much larger than the small stems. Each stem has dense, thin, upright bumps called tubercles. Tiny white spines form flat groups at their tips. Each group can hold up to 80 spines. The spines feel soft, not sharp. Fine bristles grow in the axils, the spaces between tubercles.

The flowers are rich magenta with a white throat. Round fruits range from yellow-green to reddish-green. They span about 0.013–0.016 feet [0.004–0.005 metres]. The fruit is cryptocarpic: it grows inside the stem. Once a flower falls, the stem closes over its fruit. The black seeds then ripen inside the plant. Fruits may stay there for years, even the plant’s whole life. As stems swell, a thin cover can split, freeing seeds. Some seeds escape only when an old stem breaks down. Seeds can stay able to sprout for years. Yet few fresh seeds sprout. Seeds may take several years to sprout.

Wild plants shrink in dry spells and may sink below ground. Flowers may then rise through soil from hidden stems. New stem growth does not always add to lasting plant size. Old growth shrinks at the base as new growth forms above. This shrinking with the seasons helps explain their small size. It also makes wild plants hard to find.

Collectors grow this cactus for its unusual spines and flowers. LLIFLE reports that people have grown it with success. But it warns of pressure from wild plant collecting. A group found in 2006 held many thousands of plants. This find raised past counts based on a much smaller site. The source does not share exact sites. It keeps them private because collecting could put them at risk.