Thelocactus rinconensis, synonyms including Thelocactus nidulans, is a species of cactus. It is endemic to north-east Mexico.
Thelocactus rinconensis is a small perennial gray-green cactus, growing 6 - 8 centimeters high and is between 12 - 20 centimeters in diameter. It has 20-25 ribs with marked with angular tubercles. The areolas are 2 to 2.5 centimeters apart, circular or elliptical and covered with white wooly hairs. Areoles have 3 to 4 central spines are 6 - 8 centimeters long It features up to six dark brown to black main spines and thin, radial spines that are 1.3-1.5 cm long. Flowers, about 4 cm long and 2.5-7.5 cm wide, are funnel-shaped and yellow or whitish, growing from new growth at the top of the plant. Fruits are spherical to oblong with scales, 7-9 mm in diameter, greenish or yellowish. Seeds are 1.7-2 mm long[1]
The plant is found in the Chihuahuan Desert of Coahuila and Nuevo Leon, Mexico growing at elevations of 1200-1900 meters growing in xerophytic shrubland on calcareous soils.[2]
Echinocactus rinconensis was described in The Cactaceae in 1855 by Heinrich Poselger.[3] Nathaniel Lord Britton and Joseph Nelson Rose placed the species in the genus Thelocactus in 1923.[4]