Thelocactus  Thelocactus is a genus in the cactus family, Cactaceae. Members of the genus are native to the arid lands of Central and Northern Mexico. "Thelocactus" species are globe-shaped, short and cylindrical. They are small cacti, although there are one or two species which, while only about 15 cm high, can be 25 cm in diameter; for example, "T. nidulans". "Thelocactus" species are generally solitary, but some varieties will cluster in groups. The ribs on "Thelocactus" species are very clearly marked and are sometimes twisted in a spiral. There can be from 8 to 20 ribs, which are rather low and normally marked with raised, angular or hexagonal tubercles. These tubercles can sometimes be difficult to distinguish. Areoles sit in a furrow directly above where the spines grow and there can be up to twenty radial/radiating spines. They are often needle-like, spread out and can be from 1.3 – 1.5 cm long. The central spines are mostly coarser, number up to six, stand vertically out from the plant and can be 2.5 – 7.5 cm long. Colours of all of the spines vary and include white, gray, golden-yellow and red-brown. Flowers grow from the new areoles at the very top of the plant. They are funnel-shaped, have a diameter of 2.5 – 7.5 cm and their colours vary from white to shades of yellow, red or purple. They are diurnal. Fruits are small, globe-shaped and plain. They are dehiscent through the large basal pore, green to brownish purple [to magenta], spherical to short cylindrical, 5 - 18 x 6 – 17 mm, not juicy, drying immediately after ripening, scaly, spineless, hairless and with floral remnant persistent. "Thelocactus" species grow in the wild in central and North Mexico and in the US in Texas. In Mexico, the species are generally concentrated along and to the west of the Sierra Madre Oriental beginning with "T. hastifer" in Querétaro State, about 150 km NNW of Mexico City. One subspecies ("T. bicolor ssp. flavidispinus") grows on the other (northern) side of the Rio Grande, well distributed in the Big Bend area of Texas.