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Thelocactus bicolor ssp. heterochromus is heavily armed with amber to reddish spines and produces magenta flowers with a reddish throat in spring.
 

Description: Usually solitary. Like many cactus forms of dry, hot region of Mexico, plants are strongly variable; therefore a precise description is impossible.
Stem: Depressed to globose, 4-7 cm tall, 6-15 cm wide.
Ribs: 8, distinct.
Tubercles: rounded.
Areoles: Without glands.
Central spines: 1-4, 20-50 mm long, ochre to reddish, straight, subulate.
Radial spines: 6-10, 16-40 mm long, ochre to reddish, straight, acicular to subulate.
Flowers: 45-80(-100) mm wide, Deep pink- magenta with a red throat , base orange,
Blooming season: Flowers appear exclusively from June through August.

NOTE: 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.

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Scientific name:   Thelocactus bicolor ssp. heterochromus (Weber) Mosco & Zanovello
Published in: Bradleya 18: 62 (2000).

Basionym: Echinocactus heterochromus F.A.C. Weber,
Dict. Hort. Bois. 466 (1896).
Lectotype: 3.5 km al Oeste de la Soledad, Durango, R.D. Worthington 10902 (TEX).

Conservation status: Listed in CITES appendix 2

Origin: Northeastern Mexico (Durango, Coahuila)

Habitat: Grows in matorral xerofilo on limestone hills.

Synonyms:

• Thelocactus heterochromus (Web.) Van Oosten
  Kakteenkunde 58 (1940).
• Echinocactus heterochromus F. A. C. Weber
  In: " French garden lexicon " 1896
• Thelocactus heterochromus (F. A. C. Weber) van Oosten 1940
• Ferocactus heterochromus (F. A. C. Weber) N. P. Taylor
  Cact. Succ. J. Gr. Brit. 41: 90 (1979).
• Echinocactus bicolor var. pottsii Salm-Dyck,
  Cact. Hort. Dyck. 173 (1850).

Cultivation: It is a summer grower species of low maintenance.  Water regularly from Spring to Autumn, but do not overwater, can become too elongated if compost is too rich. Requires full sun or light shade and careful watering to keep plant compact with strong coloured spines. Needs good drainage and very porous potting mix, In Winter, keep dry.
Reproduction: From seed, since the plant rarely produces plantlets.

This is one of most beautiful Thelocactus. But, unfortunately, this plant is supplied only, rarely, sometimes by the name Thelocactus pottsii.

Photo of conspecific taxa, varieties, forms and of plants belonging to the Thelocactus bicolor complex (This Taxon has lots of synonyms ( like many other cacti) whit several controversial varieties and subspecies and comprises a multitude of different forms, but where each form is linked to others by populations of plants with intermediate characteristics):
 

• T. bicolor var. bicolor (Frost hardiness -7°C )
• T. bicolor var. bolaensis (Frost hardiness -12°C ) Origin: Coahuila from Sierra Bola, up to 20 cm tall.
• T. bicolor var. commodus  It has been described as having only one, porrect, central spine, but with a careful observation it is possible to notice that the upper central spines are so appressed to the stem that they can be easily mistaken for radials.
• T. bicolor var. ellipticus is referable to bicolor.
• T. bicolor var. flavidispinus (Frost hardiness -12°C ) Texas 8cm in diameter, 5cm tall.
• T. bicolor var. heterochromus
• T. bicolor var. pottsii (Referable to bicolor var. heterochromus).
• T. bicolor var. rhodophthalmus is referable to bicolor.
• T. bicolor var. schottii (Frost hardiness -12°C) coming from the Big Bend area Texas, Chihuahua) characterized by a very long, papery upper spine.
• T. bicolor var. schwarzii 1 0° F (-12°C) Tamaulipas
• T. bicolor var.  texensis is an invalid name for a Texas form.
• T. bicolor var. tricolor (Frost hardiness -7°C ) A form with bright red spines. Plants with these characters can be found around Saltillo, Coahuila.
• T. bicolor var. zwakii,  It is not sufficiently distinct to deserve a subspecies rank.

Cultivars: Thelocactus bicolor cv. INERMIS

All the information and photos in cactus art files are now available also in the new the Enciclopedia of Cacti. We hope you find this new site informative and useful.