Mammillaria melanocentra

Mammillaria melanocentra is a small perennial cactus from northern Mexico. It belongs to the cactus family, Cactaceae. Kew lists its range as southeastern Coahuila and western Nuevo León. LLIFLE gives a wider range, adding Durango and Tamaulipas. It grows in desert and dry shrubland. Wild plants occur on steep cliff faces and flat shrubland sites. They grow at heights of about 1,150–5,900 feet [350–1,800 metres] above sea level.

Plants tend to form one head rather than a clump. The stem is squat and round, or forms a short cylinder. Its top is somewhat flat, and its skin is blue-green. Stems reach about 0.52 feet [0.16 metres] tall. Their usual width is 0.33–0.39 feet [0.10–0.12 metres]. Some reach 0.49 feet [0.15 metres] across. Large, firm tubercles cover the stem in spirals. Each has four clear angles and a raised ridge. Young spaces between the tubercles hold thick white wool, without bristles. The plant contains latex.

Stout spines add to the plant's dense outline. The radial spines vary in length and colour. They may be white, brownish, or black. The lowest radial spine is the longest. Each cluster usually has one central spine, though some have three. These strong, awl-shaped spines tend to point upward. They start black and fade to grey or brownish grey. Central spines reach about 0.07–0.10 feet [0.02–0.03 metres] long.

Flowers form a ring around each head in spring. Bloom lasts for several weeks. The star-shaped flowers range from whitish to deep pink-red or carmine. A darker stripe marks the centre of each narrow, pointed segment. Each flower measures about 0.07 feet [0.02 metres] across and long. The club-shaped fruit turns pink to scarlet. It reaches about 0.10 feet [0.03 metres] long and holds brown seeds.

LLIFLE describes this cactus as easy to grow and willing to flower. Give it regular summer water, but avoid excess watering. Keep it dry through winter. The source reports cold tolerance down to 25°F [-4°C]. Grow new plants from seed, or from offsets when available. Its compact stem, strong spines, and flower ring provide ornamental interest. In the wild, illegal collection and goat grazing may threaten it.