Greek thele—nipple, referring to the nipple-like tubercles on some species.
Body low-growing, solitary or clustering, compressed spherical or shortly cylindrical with ribs or tubercles. Areoles sometimes with nectar-secreting glands. Flowers diurnal, funnel-shaped, arising at the apex of the body; mostly summer. Pericarpel and floral tube with scales that do not have hairs in the axils. Fruit dry, spherical, mostly green or brown (rarely red), opening by a hole or slit at the base.
Closely related to Neolloydia.
Seed or rarely by offsets.
Fruit opening at a basal pore.
11 species from Texas and C and N Mexico.
Anderson (1987).
Source: (1997). Cactaceae. In: . Horticultural Flora of South-eastern Australia. Volume 2. Flowering plants. Dicotyledons. Part 1. The identification of garden and cultivated plants. University of New South Wales Press.