The genus Thelocactus 

Type: Sierra de las Ovejas, Coahuila, Mexico, A. Lausser s.n. (PR 377518).

Description
Stem single, globose to short elongate, 7-10 cm tall, 5-8.5 cm wide. Ribs 8, distinct. Tubercles rounded. Areoles without glands. Central spines 4-(6), 60-105 mm long, ochre to greyish, straight or slightly curved, acicular. Radial spines 20-25, 18-28 mm long, white, straight, acicular. Flowers 25-45 mm wide, whitish to pale pink with a darker midstripe. Seeds 1.7 x 1.2 mm, testa cells convex with a verrucose surface sculpture.

Distribution
It is endemic of the Sierra de las Ovejas, in Coahuila, at elevations of about 800 to 1500 metres above sea level. Its range lies within the Central Chihuahuan subregion of the Chihuahuan Desert ecoregion.

Comments
The flowers of lausseri are the smallest of the genus (25-45 mm) and their colour is quite similar to that of some species of Stenocactus: they are white, with a pinkish central stripe. The plants start forming buds already in autumn, and the first flowers appear plentifully from the end of January to the end of February. The stem is small, ovoidal, divided into ribs, with a rather tight spination, and it reminds one of Thelocactus bicolor.