Origin and Habitat: Northeastern Mexico (Durango, Coahuila)
Habitat: Grows in matorral xerofilo on limestone hills.

• Thelocactus bicolor subs. heterochromus (F.A.C.Weber) Mosco & Zanov.
• Echinocactus heterochromus F.A.C.Weber
• Ferocactus heterochromus N.P.Taylor
• Thelocactus heterochromus (F.A.C.Weber) Oosten
• Thelomastus heterochromus (F.A.C.Weber) Frič in Kreuz.

• Thelocactus bicolor subs. heterochromus (F.A.C.Weber) Mosco & Zanov.
• Echinocactus heterochromus F.A.C.Weber
• Ferocactus heterochromus N.P.Taylor
• Thelocactus heterochromus (F.A.C.Weber) Oosten
• Thelomastus heterochromus (F.A.C.Weber) Frič in Kreuz.
• Thelocactus bicolor var. pottsii (Schur ex Salm-Dyck) Backeb.
• Echinocactus bicolor var. pottsii Schur ex Salm-Dyck
• Echinocactus bicolor f. pottsii (Schur ex Salm-Dyck) Voss in Vilm.
• Echinocactus pottsii Schur ex Salm-Dyck
• Thelocactus pottsii (Schur ex Salm-Dyck) Britton & Rose
• Thelocactus heterochromus longispinus

• Thelocactus bicolor (Galeotti ex Pfeiff.) Britton & Rose
• Cactus bicolor Teran & Berland.
• Echinocactus bicolor Pfeiff. in Pfeiff. ex Pfeiff.
• Echinocactus rhodophthalmus Hook.
• Echinocactus rhodophthalmus var. ellipticus Hook.
• Ferocactus bicolor (Galeotti ex Pfeiff.) N.P.Taylor
• Hamatocactus bicolor I.M.Johnst.
• Thelomastus bicolor (Galeotti ex Pfeiff.) Frič in Kreuz.
• Thelocactus bicolor var. commodus R.Haas
• Thelocactus bicolor subs. commodus (R.Haas) Doweld
• Thelocactus bicolor var. schottii (Engelm.) Krainz in Krainz
• Echinocactus bicolor var. schottii Engelm.
• Echinocactus schottii Small
• Thelocactus schottii (Engelm.) Kladiwa & Fittkau
• Thelocactus bicolor subs. swobodae Halda & Horáček
• Thelocactus bicolor var. texensis Backeb.
• Thelocactus bicolor var. tricolor (K.Schum.) F.M.Knuth in Backeb. & F.M.Knuth
• Echinocactus bicolor var. tricolor K.Schum.
• Echinocactus bicolor f. tricolor (K.Schum.) Schelle
• Thelocactus bicolor subs. zwakii Chvastek & Halda

• Thelocactus bicolor subs. bolaensis (C.Runge) Doweld
• Echinocactus bicolor var. bolaensis (C.Runge) K.Schum.
• Echinocactus bicolor f. bolaensis (C.Runge) Schelle
• Echinocactus bolaensis C.Runge
• Ferocactus bicolor var. bolaensis (C.Runge) N.P.Taylor
• Thelocactus bicolor var. bolaensis (C.Runge) A.Berger
• Thelocactus bicolor var. bolansis (K.Schum.) F.M.Knuth
• Thelocactus bolansis hort.
• Thelomastus bicolor bolansis (C.Runge) Frič in Kreuz.
• Thelocactus bicolor var. wagnerianus (A.Berger) Krainz in Krainz
• Echinocactus wagnerianus var. A.Berger A.Berger
• Thelocactus wagnerianus A.Berger
• Thelomastus bicolor wagnerianus (A.Berger) Frič in Kreuz.

• Thelocactus bicolor subs. flavidispinus (Backeb.) N.P.Taylor
• Ferocactus bicolor var. flavidispinus (Backeb.) N.P.Taylor
• Thelocactus bicolor var. flavidispinus Backeb.
• Thelocactus flavidispinus Backeb.

• Thelocactus bicolor subs. schwarzii (Backeb.) N.P.Taylor
• Ferocactus bicolor var. schwarzii (Backeb.) N.P.Taylor
• Thelocactus bicolor var. schwarzii (Backeb.) E.F.Anderson
• Thelocactus schwarzii Backeb.

• Thelocactus bicolor cv. albiflorus
• Thelocactus bicolor cv. inermis

Description: Thelocactus heterochromusSN|10830]]SN|15814]] is a robust-globular or somewhat squat cactus with very large rounded tubercles and areoles lacking nectar-secreting glands. This choice, slow-growing cactus is usually considered to be a subspecies of Thelocactus bicolorSN|3420]]SN|3420]]. But it looks more like a green form of Thelocactus hexaedrophorusSN|15814]]SN|10830]], with which it shares usually solitary stems with distinct, rounded tubercles armed with bold clusters of claw-like spines. The spines are a bit more slender in T. heterochromus, and, as the name implies, are often shaded different colours, from white to yellow, or red. The flowers are a gorgeous magenta, mostly 6—10 cm wide, usually with red at the base. Like many cactus forms of dry, hot region of Mexico it is strongly variable especially in spination. Therefore a precise description is impossible.
Derivation of specific name: heterochromus Greek 'heteros', different; and Greek 'chromos', colour; for the spines shaded in different colours.
Stem: Depressed to globose, usually solitary, 4-7 cm tall, 6-15 cm wide, somewhat green to bluish green (glaucous), or yellowish.
Ribs: 8 or 9(-11), very large rounded and obtuse, more or less distinctly tubercled.
Tubercles: Rounded.
Areoles: Without glands, large, closely set on old plants, densely felted when young, naked in age .
Spines: Spines variable as to number, shape, size, and colour.
Central spines: 1-4, straight, stout-subulate, more or less flattened, 20-40(-50) mm long, the lowermost down-pointed and sometimes grooved, the others curving towards stem apex, ochre to reddish often white, but sometimes banded with red.
Radial spines: 6-9(-10), straight, acicular to subulate, usually terete, straight or incurved, 16-28(-40) mm long, ochre to reddish, more or less banded with red and white or pale yellow, otherwise like the centrals.
Flowers: Like those but up to100 mm wide, Deep pink- magenta with a orange-red throat, base orange. Scales on ovary and flower-tube ovate, greenish; margins thin and ciliate. Inner perianth-segments light purple, darker at base, oblong. Stigma-lobes yellow.
Fruit: Globose, small, 1.5 cm. in diameter.
Seeds: 1.6-2.2 x 1-1.5 mm, tubercuate, black, truncate at base, ridged on back; hilum basal, white, circular.
Blooming season: Flowers appear in mid-summer (in habitat from June through August).

Notes: This is the westernmost taxon in the genus. Usually, it has a depressed to globose stem with wider ribs. Spines are stouter, subulate, banded in red. The var. pottsii applies to those entities from Chihuahua that are intermediate between "heterochromus" and "bicolor", but definitely belong to heterochromus for their lack of areolar glands.

Bibliography: Major references and further lectures
1) Nathaniel Lord Britton, Joseph Nelson Rose “Cactaceae: Descriptions and Illustrations of Plants of the Cactus Family” volume 4, 1923
2) Hirao, “Colour encyclopaedia of cacti”, f. 118 (1979)
3) Hecht, “BLV Handbuch der Kakteen”, 363 (1982)
4) David R Hunt; Nigel P Taylor; Graham Charles; International Cactaceae Systematics Group. "The New Cactus Lexicon" dh books, 2006
5) James Cullen, Sabina G. Knees, H. Suzanne Cubey "The European Garden Flora Flowering Plants: A Manual for the Identification of Plants Cultivated in Europe, Both Out-of-Doors and Under Glass" Cambridge University Press, 11/Aug/2011
6) Thelocactus heterochromus in: Cactus and Succulent Journal, Volume 81,
2009
7) Urs Eggli, Leonard E. Newton “Etymological Dictionary of Succulent Plant Names”
Springer Science & Business Media, 29 June 2013

Cultivation and Propagation: This is a summer grower species easy to cultivate, more cold tolerant than most and less fussy regarding soil conditions.
Growth rate: It is a relatively rapidly growing and easily flowering species that will make clumps given the best conditions.
Soils: It likes very porous standard cactus mix soil, but can become too elongated if compost is too rich.
Repotting: Use pot with good drainage.
Watering: Water regularly from Spring to Autumn, but do not overwater(Rot prone), keep dry in winter.
Fertilization: Feed with a high potassium fertilizer in summer.
Hardiness: Reputedly somewhat resistant to frost if kept on the dry side prior to, and during, cold weather (hardy to -7 C ° C, or less for short periods).
Exposition: Requires full sun or light shade and careful watering to keep plant compact with strong coloured spines. Tends to bronze in strong light, which encourages flowering and heavy spine production.
Uses: It is an excellent plant for container growing. It always looks good and stays small. It look fine in a cold greenhouse and frame or outdoor in a rockery.
Pests & diseases: It may be attractive to a variety of insects, but plants in good condition should be nearly pest-free, particularly if they are grown in a mineral potting-mix, with good exposure and ventilation. Nonetheless, there are several pests to watch for:
- Red spiders: Red sopiders may be effectively rubbed up by watering the infested plants from above.
- Mealy bugs: Mealy bugs occasionally develop aerial into the new growth among the wool with disfiguring results, but the worst types develop underground on the roots and are invisible except by their effects.
- Sciara Flies: Sciara flies are one of the major problems for seedlings. It is a good practice to mulch your seedlings with a layer of grit, which will strongly discourage the flies.
- Scales: Scales are rarely a problem.
It is wise to treat your whole collection with a systemic insecticide twice a year in spring and autumn.
- Rot: Rot is only a minor problem with cacti if the plants are watered and “aired” correctly. If they are not, fungicides won't help all that much.
Propagation: From seed, since the plant rarely produces plantlets. Seeds germinate in 7-14 days at 21-27° C in spring, remove gradually the glass cover as soon the plants will be well rooted (ca 1-2 weeks) and keep ventilated, no full sun for young plants!