Aztekium ritteri aka Aztec Cactus

Aztekium ritteri is a small cactus native to Mexico. It belongs to the cactus family, Cactaceae. Kew lists Nuevo León, Coahuila and San Luis Potosí. LLIFLE gives a narrower range within Nuevo León. There, it grows on steep cliffs in dry scrub. Its sites include soft limestone and gypsum rock faces. It favours slopes that face north over sunnier sites. Some colonies grow on cliffs that people cannot reach.

The rounded body seldom exceeds 0.16 feet (0.05 metres) across. Its height is a little less than its width. Nine to eleven rounded ribs run along the body. Many crosswise grooves give these ribs a wrinkled look. Shorter ribs fill the gaps between the main ones. These reach about halfway up the body. New growth has a pale, yellow-green shade. Older growth turns grey-green near the base. White wool gathers at the growing tip. Each areole may bear one to three small, weak spines. The youngest areoles may have no spines at all.

Mature plants slowly form offsets and can make small clumps. They do not form a large root for storage. Growth is very slow, at around one millimetre each year. Small flowers emerge from the tip through the summer. Each measures less than 0.033 feet (0.01 metres) across. Their petals range from white to pink. Outer petals often carry a darker stripe down the middle. Small pink fruits follow the flowers. They split at maturity and release very fine seeds.

Raising this cactus from seed demands close care and patience. LLIFLE reports germination rates below five percent. The seedlings remain fragile during their first two months. Even a drop of water can shift their tiny bodies. Many seedlings die before reaching a more robust size. Growers use grafting to speed growth. Grafted plants may become plumper and produce more offsets. These offsets may also appear higher on the body.

Illegal collection poses a threat to wild plants. Erosion also removes parts of their cliff habitat. Remote sites give some colonies protection from collectors. The supplied sources give no firm hardiness limits or watering schedule. They also provide no evidence about food use or toxicity.