– Thelocactus (2011)

By Eric Driskill (November 2011)

The genus Thelocactus is in the subfamily Cactoideae and the tribe Cacteae. The name thelocactus is derived from the Greek thele, nipple, thus “nipple cactus.” Thelocactus are found from central Mexico to Texas, from sea level to an altitude of 7,200 feet.

Thelocactus leucacanthus was discovered around 1830 by Karwinski near Zimapan in central Mexico north of Mexico City. It was first placed in Echinocactus and later raised to the rank of genus by Britton and Rose (1919-1923) with T. hexaedrophorus the type species. The number of Thelocactus species varies by author. Anderson recognizes 12 in The Cactus Family.

The plants are either solitary or clustering, globose or columnar, from 1 to 10 inches high and 0.8 to 8 inches in diameter. Thelocactus plants have seven to 20 ribs, some of which spiral. Tubercles are usually present. Spines vary within the genus, with zero to five central spines, 0.2 to 2.5 inches long. The straight radial spines range up to 2.4 inches long. Flowers are borne at the tips of the tubercles.

This genus represents the iconic picture of cacti, with many globular species and the occasional columnar plant. On a cursory glance, many Thelocactus species could be confused with mammillarias until they bloom. The blooms are from 0.8 to 3.1 inches, whereas mammillaria blooms are typically much smaller.

Another distinction is that Thelocactus blooms are borne at the tips of the tubercles, and mammillaria blooms arise from the base of the tubercles. Thelo blooms are often quite showy in both size and color, ranging from white and yellow to pink and magenta.

Thelocactus bicolor is a nice choice for its spine color, which ranges from yellowish white to purple and contrasts nicely with the green plant body. Its flowers are also large — up to 3 inches in diameter and a nice shade of magenta.

Another nice selection not too difficult to find on sales tables is T. rinconensis subsp. rinconensis. While its blooms are “just” up to 1.2 inches and a white to light pink, the globose body shape, the shape of the tubercles and long spines would make this a beautiful addition to your collection.

Check out one of these two plants or any of the other species. They don’t pose a particular challenge in cultivation apart from the ordinary fare of well-draining soil and a monitored watering schedule.

Sources:
The Cactus Family – Anderson, E. F.
Thelocactus Site – http://thelocactus.cactus-mall.com