Stem tubercles 6-21 mm. Radial spines usually 16-30 per areole. Flowers 2.2-5.1 cm diam. Fruits 6-15 mm diam. Flowering summer; fruiting fall. Semidesert grasslands, Madrean pine-oak woodlands, steep, rocky slopes, canyons, and valleys, usually on alluvial or igneous substrates; 1100-2000 m; Ariz., N.Mex.; Mexico (Chihuahua, Sonora). In rocky habitats near the Mexican border, populations of Mammillaria wrightii var. wilcoxii tend to have more radial spines and smaller flowers than elsewhere and have been segregated as M. meridiorosei. Almost half of the published descriptions and illustrations purporting to represent variety wilcoxii are misidentifications of Mammillaria viridiflora.

Benson 1982, FNA 2003

Common Name: Wilcox's nipple cactus Duration: Perennial Protected Status: Salvage restricted status in Arizona, endangered in New Mexico. General: Low globose cactus that is usually unbranched stems with tubercles 6-21 mm, the stem spheric or flat-topped. Spines: Radial spines 16-30 and straight, these wrapping parallel around stem with 1-5 central spines that are all hooked. Flowers: Flower 22-48 mm diameter with fringed outer tepals and inner tepals that are rose-pink or magenta and lanceolate linear and spreading widely but forming a shallow bowl, the anthers are yellow, the style reddish-purple to green, the flowers form a circle near the stem apex. Fruits: Fruits dull purple or green and spheric to obovoid, 9-20 mm long by 6-15 mm diameter and juicy throughout with a persistent floral remnant, generally flowering after summer rains. Ecology: Found in semi-desert grasslands, woodlands, steep, rocky slopes, canyons, and valleys, on alluvial or igneous substances from 3,500-5,000 ft (1067-1524 m). Notes: Appears similar to M. wrightii var. wrightii, except that it has a greater number of radial spines (16-30). Also, flowers and fruits and generally smaller than M. wrightii or var. wrightii, (with fruits 6-15 mm in diameter). Prefers lower elevations and is considered rare in many counties in Arizona. According to FNA, when this plant is found in rocky habitats near the Mexican border those individuals with more radial spines and smaller flowers than elsewhere have been segregated as M. meridiorosei . FNA also notes that half the published descriptions and illustrations thought to represent var. wilcoxii are misidentifications of Mammillaria viridiflora. Ethnobotany: Specific use of variety is unknown, however the stems and ripe fruit of the genus were used as food. Etymology: Mammillaria comes from the Latin mammilla, a nipple, while wrightii is named after Charles Wright (1811-1855), an American botantical collector who collected plants for Professor Asa Gray at Harvard, and later worked on the Mexican Boundary Survey, collecting plants for Professor John Torrey. Synonyms: Mammillaria wrightii var. wilcoxii Editor: LCrumbacher, 2010