Thelocactus bicolor subs. heterochromus

Publication: Bradleya 18: 62 (2000)

Description

Thelocactus heterochromus 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 bicolor. But it looks more like a green form of Thelocactus hexaedrophorus, 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).

Origin and Habitat

Northeastern Mexico (Durango, Coahuila)

Habitat: Grows in matorral xerofilo on limestone hills.

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!

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

Nathaniel Lord Britton, Joseph Nelson Rose “Cactaceae: Descriptions and Illustrations of Plants of the Cactus Family” volume 4, 1923
Hirao, “Colour encyclopaedia of cacti”, f. 118 (1979)
Hecht, “BLV Handbuch der Kakteen”, 363 (1982)
David R Hunt; Nigel P Taylor; Graham Charles; International Cactaceae Systematics Group. “The New Cactus Lexicon” dh books, 2006
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
Thelocactus heterochromus in: Cactus and Succulent Journal, Volume 81,

2009

Urs Eggli, Leonard E. Newton “Etymological Dictionary of Succulent Plant Names”

Springer Science & Business Media, 29 June 2013

From llifle page Echinocactus bicolor var. pottsii

Description

Usually solitary the Thelocactus bicolor var. pottsii is one of most beautiful Thelocactus. Unfortunately this plant is supplied only, rarely, sometimes by the name Thelocactus heterochromus.

Stem: Large, globular, low-growing, green, reach hardly 15 cm in diameter and get 10-15 cm tall. Epidermis - bluish-sulphur- green that became almost red-brown during the winter rest when the plants are dry.

Tubercles: Rounded that form 8-11 (usually 9) distinct ribs.

Areoles: Round, on the outer side of tubercle bear semicircular heavy cut.

Spines: 7-11 (-19), powerful, very different in length, thickness and colour.

Central spines: 1-2 (or more) bent back and newly bent to the body the upper one is flattened, red- white colored, the spines produced in spring are brighter and redder while the one produced the hot period of year are paler, some plants have very short spines, whose central prickle has a length of only of 1,5 cm, but there are plants with 5,5 cm long spines. The name “heterochromus” (= many-colored) indicates patch effect of prickles, but it can be also applied to the variable colours of spines in different plants.

Radial spines: 9-11 (-18) 1,5-3 cm long, yellowish strong, awl-shaped, usually bent downward.

Flowers: Imposing 8-10 cm in diameter pink-violet lobes with a dark red throat and yellowish orange anthers.

Blooming season: Flowers appear exclusively from June through August.