Thelocactus setispinus aka Miniature Barrel Cactus

Thelocactus setispinus is a small cactus in the Cactaceae family. Its common names include hedgehog cactus, fishhook cactus, and twisted rib. The RHS also lists the older name Hamatocactus setispinus. Its native range runs from southern Texas into northeastern Mexico. In Texas, it grows in Cameron, Hidalgo, and Starr counties. Its Mexican range includes Coahuila, Nuevo León, and Tamaulipas. It grows in dry scrub and coastal lowlands beneath mesquite. Wild plants occur from sea level to about 1,800 feet [550 metres].

Most plants grow as a single stem with long, fibrous roots. Some sprout near the base and form two or three branches. Others branch higher up or develop into larger clumps. Young stems are round or slightly stretched in shape. With age, they become more like short columns. Stems reach about 0.23–0.49 feet [0.07–0.15 metres] tall. Larger examples can reach 0.98 feet [0.30 metres]. Each stem measures about 0.16–0.30 feet [0.05–0.09 metres] across. Stem size varies between wild populations.

The stem ranges from yellow-green to a dull blue-green. It has 12–15 thin, raised ribs with wavy edges. The ribs may slant or twist around the stem. Small spine-bearing pads, called areoles, sit along these ribs. These pads also bear glands that make nectar outside the flowers. Each areole carries nine to seventeen slender radial spines. These spread outward and range from white to brown. One to three central spines rise beyond the radial spines. Their colour ranges from pale yellow-white to red. A hooked central spine helps explain the name fishhook cactus.

Flowers appear in a series through summer and autumn. Their yellow petals surround a deep red centre. Each flower has a clear tube and spreads open above it. Flowers measure about 0.10–0.13 feet [0.03–0.04 metres] across. Their length can reach 0.23 feet [0.07 metres]. The inner petals have pointed tips and spread widely. Pale yellow to white lobes form the stigma. Round or egg-shaped red fruits follow the flowers. They have white flesh and a few surface scales. The ripe fruits stay closed rather than splitting open. Their small seeds have a finely bumpy surface.