Thelocactus conothele var. argenteus Glass & Foster, Cact. Succ. J. (US) 44: 48 (1972).

Thelocactus conothele var. argenteus Glass & Foster var. nov.
   A var. typica spinis magis numerosis et natura coloreque spinarum differt.
   Spinae argenteo-albae, basi cinereae, centrales 4, cremeo-albae juventute, apice flavo-brunneae, demum fibrillosae et argenteae, 1 mm. diam.; spina infima porrecta, basi vix incrassata, 35-40 mm. longa; spinae superiores centrales 30-50 mm. longae; radiis 20 vitrei, argenteo-griseo-albi, inferiores ca. 13 mm. longi, laterales et superiores 20-30 mm. longi, duplo vel triplo longiores quam distancia inter areolas.

BODY: solitary, sub-globose, ca. 13 cm. in diameter, ca. 8 cm. high, pale green. Ribs completely divided into prominent tubercles which are obscured by the spines.
TUBERCLES: arranged in 13 and 21 spirals, basally keeled, ca. 10-15 mm. wide and 12-17 mm. long at base, ca. 10 mm. high.
AREOLES: wooly when young.
SPINES: silvery white, dirty gray at the base. Central spines 4, creamy white when young, tipped yellow brown, becoming shredded and silvery with age, 1 mm. thick; lowest spine porrect, only slightly thickened at the base, 35-40 mm. long; upper centrals 30-50 mm. long. Radials glassy, silvery grayish white, 20; lower radials ca. 13 mm. long; lateral and upper radials 20-30 mm. long, 2 to 3 times longer than the distance between the areoles!
FLOWERS: 35 to 40 mm. long, scales on tube 2.5 to 3 mm. wide with aristate tip and wide, hyaline, finely fimbriate margin, brownish green to purple mid-stripe; outer perianth segments scale-like but more elongated and with entire margins; inner perianth segments ca. 5 mm. wide, pink to purple with a faintly darker mid-line, margins entire, tip finely aristate. Style 28 mm. long. anthers bright yellow.
FRUIT: with scales, basally dehiscent, dried fruit 12 mm. long, 7 mm. in diameter, dried perianth persisting.
SEED: very dark reddish purple to black, with finely tuberculate testa; ca. 1.5 mm. in diameter with large hilum; somewhat irregular in shape with a constriction around the middle.
TYPE LOCALITY: Mountain ridges between the towns of Ascension and Sandia in Nuevo Leon, about 7 miles west of Ascension.
HOLOTYPE: Glass & Foster #3176, collected February 12th, 1971, deposited at the Zürich Succulent Collection (Stadt Sukkulentensammlung) and isotypes were deposited at the Pomona College Herbarium and at the Herbarium of the Universidad Nacional Autonoma de Mexico.

   This variety differs from the type principally by its greater spine count, the distinctive nature and color of the spines, and by its isolated range.
We are naming this variety of Thelocactus conothele for the distinctive silvery appearance of the shredding spines. The remarkable characteristic of shredding spines also occurs in Thelocactus nidulans and to a lesser extent in T. rinconensis. We had first seen this striking plant in the collection of Ing. Gustavo Aguirre Benavides of Parras and at first glance thought the plant to be a form of Thelocactus macdowellii, a closely related species. Our friend, Don Gustavo, kindly supplied us with the locality information.
   At the time the plants were collected, they were nearly all in flower. It is very abundant along the ridge of the hill where it grows in full sun, but we saw no plants on the slopes or near the base. At the same locality one can also find Yucca carnerosana, Agave lechuguilla, Thelocactus bueckii, Mammillaria candida, M. cf. formosa and Echinocactus platyacanthus.