About Thelocactus leucacanthus (Zucc. ex Pfeiff.) Britton & Rose
Thelocactus leucacanthus grows in clusters or forms large multi-headed cushions that can reach up to 80 cm (31 inches) across. Individual yellowish-green plants are shaped like globes or short cylinders, growing 4.5 to 15 cm (1.8 to 5.9 inches) tall and 2.5 to 5 cm (0.98 to 1.97 inches) in diameter. This cactus has 7 to 14 tuberous ribs that run vertically or spiral around the stem, with conical cusps that grow up to 1.1 cm (0.43 inches) high, 1.4 cm (0.55 inches) wide, and 0.8 cm (0.31 inches) long. Its areoles, which reach up to 6 mm (0.24 inches) long and 3 mm (0.12 inches) wide, bear extrafloral nectaries. Occasionally, a single yellowish-white to nearly black central spine grows up to 5 cm (2.0 inches) long; this species also has 6 to 20 radial spines, which measure 7 mm (0.28 inches) long and are either straight or slightly curved. Its flowers may be yellow, purple, or crimson, and reach up to 5.2 cm (2.0 inches) long and 4.5 cm (1.8 inches) in diameter. Its green to yellowish fruits grow up to 9 mm (0.35 inches) long and 8 mm (0.31 inches) wide, drying and cracking at the base when they ripen. The fruits hold seeds that are up to 2 mm (0.079 inches) long and 1.8 mm (0.071 inches) wide, with polygonal or square testa cells. This species is found growing at elevations between 1200 and 1900 meters in the succulent bush forests of Hidalgo and Querétaro, Mexico, where it grows alongside Thelocactus hastifer.
