Nathaniel Britton and Joseph Rose (1919-1923) described a number of genera as new in The Cactaceae. In the case of Thelocactus (type, Echinocactus hexaedrophorus = T. hexae-drophorus) they simply raised to the rank of genus a name used for a subgenus of Echinocactusby Karl Schumann (18971898), who had included 22 species in the group. Britton and Rose reduced the number of species in the genus Thelocactus to 12, including only 6 of Schumann's species. The name Thelocactus is derived from the Greek thele, nipple, thus nipple cactus. Definitive studies of Thelocactus have been published by Mark Ralston and me (Anderson and Ralston 1978), Anderson (1987), and John Pilbeam (1996).

The 12 species of Thelocactus have stems that may be single or in clusters, globose to cylindrical, usually with distinct tubercles. The areoles sometimes have partially developed grooves, but the flowers are borne at the tips of the tubercles and are open during the day in spring and summer. Fruits dehisce by basal pores.

Thelocactus (K. Schumann) Britton & Rose 1922 Echinocactus subg. Thelocactus K. Schumann 1898 Hamatocactus Britton & Rose 1922 Torreyocactus Doweld 1998

Subfamily Cactoideae, tribe Cacteae. Plants single or clustering. Stems globose to columnar, 3-25 cm (1.2-9.8 in) high, 2-20 cm (0.8-7.9 in) in diameter. Ribs 7-20, distinct or indistinct, vertical or spirallng. Tubercles usually present, rounded to conical and nipplelike. Areoles round to elongate, sometimes with partially developed grooves, borne on the tips ofthetubercles, sometimes with extrafloral nectaries. Spines extremely variable, tending to be persistent. Central spines 0-5, usually present, mostly erect, straight except hooked in one species, 5-60 mm (0.2-2.4 in) long. Radial spines 0-25, usually radiating, straight, 3-36 mm (to 2.4 in) long. Flowers borne at the tips of youngtubercles, open during the day, variable in color, funnelform, 2-8 cm (0.8-3.1 in) in diameter; pericarpels scaly. Fruits green to bright red, mostly dry at maturity, dehiscing by basal pores except in Thelocactus setispinus, scaly, round to somewhat elongate; perianth parts persistent. Seeds black, pear shaped, warty (verrucose) or with polygonal ridges (tessellate), 1-2.3 mm long, 0.5-1.7 mm in diameter. Distribution: mostly on limestone soils of the Chihuahuan Desert, dry scrub land, succulent shrub forest, thorn scrub, desert grassland, and savanna in Texas and throughout northern and central Mexico from sea level to more than 2200 m (7200 ft).

Thelocactus bicolor (Galeotti ex Pfeiffer) Britton & Rose 1922 GLORY OFTEXAS, STRAW SPINE CACTUS, TEXAS PRIDE Echinocactus bicolor Galeotti ex Pfeiffer 1848, Hamatocactus bicolor (Galeotti ex Pfeiffer) I. M. Johnston 1924, Ferocactus bicolor(Galeotti ex Pfeiffer) N. P. Taylor 1979 Echinocactus bicolor\var.] pottsii Salm-Dyck 1850, Thelocactus pottsii (Salm-Dyck) Britton & Rose 1923, T. bicolorvar. pottsii (Salm-Dyck) Backeberg 1962 Echinocactus rhodophthalmus W. J. Hooker 1850 Echinocactus bolaensis Runge 1889, Thelocactus bicolorvar. bolaen-sis (Runge) A. Berger 1929, Ferocactus bicolorv ar. bolaensis (Runge) N.P.Taylor 1979 Echinocactus bicolorvar. tricolor K. Schumann 1898, Thelocactus bi-

colorvar. tr/co/or(K. Schumann) F. M. Knuth 1935 Echinocactus schottii (Engelmann) Small 1903, E. bicolorv ar. schottii Engelmann 1856, Thelocactus bicolorvar. schottii (Engelmann) Krainz 1961, T. schottii (Engelmann) Kladiwa & Fittkau 1975 Echinocactus wagnerianus A. Berger 1929, Thelocactus wagnerianus A. Berger 1929,7. bicolorv ar. wagnerianus (A. Berger) Krainz 1961 Thelocactus flavidispinus Backeberg 1941, Ferocactus bicolorv ar. flavidispinus (Backeberg) N. P.Taylor 1979, T. bicolor subsp. flavidispinus (Backeberg) N. P.Taylor 1998 Thelocactus schwarzii Backeberg 1950, Ferocactus bicolorv ar. schwarzii(Backeberg) N. P.Taylor 1979, T. bicolorvar. schwarzii (Backeberg) E. F. Anderson 1987, T. bicolor subsp. schwarzii (Backeberg) N. P. Taylor 1998 Thelocactus bicolorv ar. texensis Backeberg 1962, not validly published Thelocactus bicolorv ar. commodus Haas 1988

Plants usually single but sometimes clustering. Stems globose to elongate, green to yellow-green, 1.5-38 cm (0.6-15 in) high, 2-18 cm (0.8-7.1 in) in diameter. Ribs 8-13, usually vertical. Tubercles 6-12 mm (0.2-0.5 in) long, 5-30 mm (0.2-1.2 in) wide, 3-18 mm (to 0.7 in) high. Areoles often with furrows, 6-10 mm (0.2-0.4 in) apart, with extrafloral nectaries. Central spines 0-5, variable in color from yellowish white to reddish purple, spreading or erect, straight, 1433 mm (0.6-1.3 in) long. Radial spines 8-17, yellowish white to reddish purple, spreading radially or erect, straight or curved, needle-like to flattened, 10-27 mm (0.4-1.1 in) long, sometimes as long as 45 mm (1.8 in). Flowers light magenta above, sometimes fading to white and then always very dark below, 3.5-6.2 cm (1.4-2.5 in) long, 4-8 cm (1.6-3.1 in) in diameter. Fruits yellowish brown or greenish brown, dry at maturity, 7-17 mm (0.3-0.7 in) long, 6-12 mm (0.20.5 in) in diameter, dehiscing by basal pores. Seeds 1.1-1.5 mm in diameter, warty. Distribution: the most widespread species of the genus, occurring in Texas and throughout northern Mexico mostly in the Chihuahuan Desert and Ta-

maulipan thorn shrub vegetation, from sea level to 2000 m (6600 ft).

Three subspecies of Thelocactus bicolor are recognized. By far the most widespread is subspecies bicolor, which has extremely variable spination, 1-4 central spines, 8-15 radials, and usually bicolored flowers; it occurs widely throughout much of the Chihuahuan Desert of Texas and Mexico and in the Tamaulipan thorn shrub vegetation along the Rio Grande. Subspecies flavidispinus has spines densely covering the entire plant, usually 3 central spines, 12-17 radials, and usually bicolored flowers; it is restricted to Caballos novaculite outcrops in modified Chihuahuan Desert vegetation in Texas and, possibly, neighboring Mexico. Subspecies schwarzii usually has no central spines, 13-14 radials, and tricolored flowers; it is restricted to Tamaulipan thorn shrub vegetation in Tamaulipas east of the Sierra Madre Oriental.

Thelocactus conothelos (Regel & Klein) Backeberg and F. M. Knuth 1935

Echinocactus conothelos Regel & Klein 1860, Gymnocactus conothelos (Regel & Klein) Backeberg 1961, Torreyocactus conothelos (Regel & Klein) Doweld 1998 ?Echinocactus smithii Muehlenpfordt 1846, ?Thelocactus smithii (Muehlenpfordt) Borg 1937, ?Neolloydia smithii (Muehlenpfordt) Kladiwa & Fittkau 1971, ?Pediocactus smithii (Muehlenpfordt) Halda 1998; Zimmerman (1991) believed that E. smithii most closely represented T. conothelos Echinocactus saussieri F. A. C. Weber 1896, Thelocactus saussieri (F. A. C. Weber) A. Berger 1929, Gymnocactus saussieri (F. A. C. Weber) Backeberg 1951 Thelocactus conothelos var. argenteus Glass & R. Foster 1972,7. conothelos subsp. argenteus (Glass & R. Foster) Glass 1998, Torreyocactus conothelos var. argenteus (Glass & R. Foster) Doweld 1998

Thelocactus bicolor subsp. bicolor

Thelocactus conothelos var. aurantiacus Glass & R. Foster 1972, T. conothelos subsp .aurantiacus (Glass & R. Foster) Glass 1998, Torreyocactus conothelos var. aurantiacus (Glass & R. Foster) Dow-eld 1998

?Thelocactus panarottoanus Halda 1998

Plants usually single but occasionally clustering. Stems globose to somewhat cylindrical, green to yellowish green, 6-12 cm (2.4-4.7 in) high, sometimes as much as 45 cm (18 in), 7-17 cm (2.8-6.7 in) in diameter. Ribs indistinct and usually spiraling. Tubercles delta shaped to elliptical, 8-24 mm (0.30.9 in) long, 4-18 mm (to 0.7 in) broad. Areoles with short furrows, usually without extrafloral nectaries, typically 1-3 cm (0.4-1.2 in) apart. Central spines 1-4, usually red to reddish white, becoming gray with age and often shedding, erect to somewhat spreading, straight, 10-55 mm (0.4-2.2 in) long. Radial spines 10-23, radiate, white to grayish brown, straight, 5-20 mm (0.2-0.8 in) long. Flowers varying in color from purple to magenta to white to yellow to orange-yellow, 3-5 cm (1.2-2 in) long, 3-4 cm (1.2-1.6 in) in diameter; pericarpels naked below but with heavy scales above. Fruits dry at maturity, 10-14 mm (0.4-0.6 in) long, 6-9 mm (0.20.4 in) in diameter, dehiscing by basal pores, scaly. Seeds

Thelocactus conothelos subsp. conothelos

1.5-2.1 mm long, 1.2-1.5 mm in diameter, warty. Distribution: eastern part of the Chihuahuan Desert of Mexico into thorn shrub vegetation and pine forest in the Sierra Madre Oriental at elevations of 1000-2100 m (3300-6900 ft).

Three subspecies of Thelocactus conothelos can be distinguished. Subspecies conothelos is usually solitary and globose, with tubercles not obscured by spines, and has 1-4 central spines, 10-16 radials, and magenta to white flowers; it is widespread in Tamaulipas, San Luis Potosí, and Nuevo León. Subspecies argenteus is solitary and globose to cylindrical, with tubercles mostly obscured by spines, and has creamy white central spines, becoming shredded with age, about 20 radials that are glassy and silvery grayish white, and pinkish purple flowers; it is restricted to pine forest near La Ascensión, Nuevo León, at elevations of about 2100 m (6900 ft). Subspecies aurantiacus is solitary, globose to somewhat cylindrical, with tubercles mostly obscured by spines, and has 4 central spines, 17-23 glassy white radials with yellowish bases, and bright yellow to orange-yellow flowers; it is restricted to a small area of the Chihuahuan Desert near Aram-berri, Nuevo León, at 1000-1200 m (3300-3900 ft).

Thelocactusgarciae Glass & M. Mendoza 1998

Plants usually solitary, sometimes forming small clumps. Stems globose, dull green, to 7.5 cm (3 in) high and 12 cm (4.7 in) in diameter. Ribs 8-13, spirally arranged. Tubercles distinct, 15 mm (0.6 in) high and wide. Areoles elongate. Central spines 4, awl shaped, bent backward slightly, gray with brown tips, to 6 cm (2.4 in) long. Radial spines of two types: lowermost 7 heavy, spreading, uppermost 7 needlelike or bristly. Flowers produced in winter, pale shiny pink with dark midveins and bases, 3-3.5 cm (1.2-1.4 in) long,

3-4 cm (1.2-1.6 in) in diameter. Fruits round, becoming elongate at maturity, purplish red, dehiscing by basal pores, to 2 cm (0.8 in) long and 1.3 cm (0.5 in) in diameter. Distribution: Bustamante, Tamaulipas, Mexico. The nature of Thelocactus garciae is problematic; it may represent a hybrid population, T. conothelos X T. tulensis. Further field studies are necessary.

Thelocactus hastifer (Werdermann 8c Boedeker) F. M. Knuth 1935

Echinocactus /last/ferWerdermann & Boedeker 1931, Ferocactus has-tifer(Werdermann & Boedeker) N. P. Taylor 1979

Plants usually solitary, cylindrical, yellowish green, 10-30 cm (3.9-12 in) high, 2.5-5 cm (1-2 in) in diameter. Ribs 12-18. Tubercles elongate vertically, 10-13 mm (0.4-0.5 in) long,

4-5 mm wide, 4-6 mm (0.2 in) high. Areoles 4-5 mm in diameter, with or without extrafloral nectaries. Central spines

Thelocactus hexaedrophorus 659

4-5, the main one erect and others radiating, white to yellowish brown, straight, 10-14 mm (0.4-0.6 in) long, sometimes as long as 26 mm (1 in). Radial spines 20-25, whitish, radiating, straight, 12-15 mm (0.5-0.6 in) long. Flowers magenta, 2.5-3 cm (1-1.2 in) long, 3.5-5 cm (1.4-2 in) in diameter. Fruits greenish purple, dry at maturity, 8-14 mm (0.3-0.6 in) long, 7-11 mm (0.3-0.4 in) in diameter, dehiscing by basal pores. Seeds 1.7-2.1 mm long, 0.5-1.1 mm in diameter. Distribution: shrubland in Queretaro, Mexico, at elevations of 1800-2000 m (5900-6600 ft).

Thelocactus heterochromus (f. a. c. Weber) Oosten 1940 Echinocactus heterochromus F. A. C. Weber 1896, Ferocactus heterochromus (F. A. C. Weber) N. P. Taylor 1979

Plants solitary, globose to depressed globose, green to bluish green, 4-7 cm (1.6-2.8 in) high, 6-15 cm (2.4-5.9 in) in diameter. Ribs 7-11. Tubercles rounded on top, 17-20 mm (0.70.8 in) long, 25-30 mm (1-1.2 in) wide, 13-17 mm (0.5-0.7 in) high. Areoles elongate, extending about half the length of the tubercle, very evident, 4-7 mm (to 0.3 in) long, typically 16-20 mm (0.6-0.8 in) apart, without extrafloral nectaries. Central spines 1-4, reddish yellow, becoming darker with age, slightly curved and pointing downward, 20-30 mm (0.8-1.2 in) long. Radial spines 6-9, white to reddish yellow, radiating, more or less straight but the uppermost one distinctly curved, 16-28 mm (0.6-1.1 in) long, 1.5-2.5 mm broad. Flowers magenta, becoming dark basally, 4.5-5.5 cm (1.8-2.2 in) long, 5.5-10 cm (2.2-3.9 in) in diameter; peri-carpels covered with heavy scales. Fruits globose to elongate, slightly fleshy at maturity, 23-30 mm (0.9-1.2 in) long, 1517 mm (0.6-0.7 in) in diameter, dehiscing by basal pores, with scales. Seeds 1.6-2.2 mm long, 1-1.5 mm in diameter, distinctly warty. Distribution: western edge of the Chihua-huan Desert of Chihuahua, Durango, and probably Zacatecas, Mexico, at elevations of 1200-1400 m (3900-4600 ft).

Continue reading here: Thelocactus hexaedrophorus Lemaire Britton Rose 1922

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