Synonyms:

Echinocactus conothelos
Echinocactus saussieri
Echinocactus smithii
Gymnocactus beguinii var. smithii
Gymnocactus conothelos
Gymnocactus saussieri
Neolloydia smithii
Pediocactus smithii
Thelocactus conothelos var. sniceri
Thelocactus saussieri
Thelocactus saussieri var. longispinus
Thelocactus smithii
Torreycactus conothele
Torreycactus conothelos

Habitat:

Thelocactus conothelos is widely distributed and plentiful in the Mexican states of Nuevo León, San Luis Potosí, and Tamaulipas. Its range covers an area close to 20,000 square kilometers, primarily existing at altitudes ranging from 1200 to 2200 meters above sea level.
In its natural habitat, this species thrives in xerophytic shrubland, specifically in matorral xerofilo, situated on limestone hills. It coexists with various other plant species such as Mammillaria candida, Mammillaria picta, Mammillaria arroyensis, Mammillaria crassimammillis, Turbinicarpus schmiedickeanus v. gracilis, Thelocactus bicolor, Astrophythum myriostigma, and Echinocactus platyacanthus. The geographic range of Thelocactus conothelos falls within the Meseta Central subregion of the Chihuahuan Desert ecoregion.

Description:

Thelocactus conothelos is a charming single-stemmed cactus with large rounded tubercles and pink flowers. It’s known for blooming early. Like many cacti from the dry, hot regions of Mexico, these plants can vary significantly in appearance. Thelocactus conothelos has been given various names, but the only acceptable distinctions are the main type and two subspecies: argenteus, which has dense silvery spines, and aurantiacus, which has orange flowers.
The plant usually grows alone but can occasionally form clusters. Its stem is round, elongated, or somewhat cylindrical, ranging from 6 to 45 cm in height and 7 to 17 cm in width. The color of the stem can vary from yellowish green to greyish green or pale green. Instead of distinct ribs, it has upward-pointing spiral tubercles. The lower tubercles are cone-shaped, delta-shaped, or elliptical, measuring 12-24 mm in length and 4-18 mm in width.
Areoles, small areas from which spines grow, can have short furrows and may or may not have nectar-secreting glands. Upper areoles are oblique and covered in white fuzz, typically spaced 1-3 cm apart. The cactus has 1-4 central spines, thicker and longer than the radial spines, ranging in color from ochre to dark blackish-brown. They can be nearly straight or slightly curved, measuring 1-9 cm in length. There are also 7-23 needle-like radial spines, usually white or greyish-brown, spreading out and measuring 5-20 mm long.
The flowers are 3-5 cm long and 4-6 cm in diameter, with a narrow tube. They are mostly magenta, although there’s a population with white and magenta flowers near Matehuala. The fruit is spherical-oblong, dry at maturity, and measures 10-14 mm long and 6-9 mm in diameter. The plant produces one or two seeds, which are conical and pointed, with a smooth surface, measuring 1.5-2.1 mm in length and 1.2-1.5 mm in width.

Cultivation:

This summer-growing plant is highly valued among collectors due to its relatively easy cultivation. It thrives in extremely dry soils, making it essential to avoid over-watering, particularly in poorly ventilated environments. The growth rate is slow, and it requires an open mineral, sandy-gritty cactus compost with excellent drainage.
For optimal development, provide a sunny-bright exposure, although it can tolerate light shade. Adequate sunlight is crucial for preventing poor growth and unnatural shapes. The plant exhibits good heat tolerance but must be shielded from excessive moisture.
Water sparingly, ensuring complete dryness during winter and when night temperatures drop below 10° C. Mature specimens are susceptible to rot, especially after transplanting, so caution is needed with watering, especially in larger pots. Fertilize once during the growing season with a cactus and succulent-specific fertilizer, diluted to half the recommended strength, to avoid excess vegetation.
Proper ventilation is crucial for this xerophytic plant, as overwatering and poor ventilation can lead to various problems, especially in dull and humid weather conditions. It thrives in warm temperatures, with a recommended minimum winter temperature of 5° C. While it can withstand moderate frost when kept dry, it’s best to provide protection in colder climates.
In terms of pests, watch out for red spiders, mealy bugs, scales, thrips, and aphids. Regular misting can help control red spiders, while mealy bugs may affect new leaves and flowers, particularly underground on the roots. Adequate watering and ventilation reduce the risk of rot, as fungicides are not always effective if these conditions are not met.

Propagation:

Propagation of this plant is primarily achieved through seed germination since it infrequently produces offsets. To start the process, sow the seeds in pots filled with fine, well-drained sandy soil, preferably in the warm temperatures of spring. Ensure that the seeds are covered with a thin layer of grit, and implement bottom watering with a fungicide to prevent damping off.
For the initial 1-2 weeks, cover the pots with a sheet of glass or clear perspex to maintain high humidity levels. Following this period, replace the glass with light shade-cloth and mist the pots once or twice daily for the next two weeks. During this time, most seeds should germinate. Subsequently, reduce misting frequency to every second and then every third day as the young plants continue to grow.
It is crucial to refrain from disturbing the seedlings until they establish strong roots. Once rooted, transplant them individually into small pots. Occasionally, grafting is employed as an alternative propagation method to mitigate root rot issues. Grafting onto a hardy stock simplifies the cultivation process, requiring no specialized skills. This approach ensures robust growth and facilitates easier care.

Curiosity:

Thelocactus conothelos, along with its subspecies argenteus and aurantiacus, as well as the closely related species Thelocactus flavus and Thelocactus garciae, stands out as markedly distinct within the Thelocactus genus. These distinctions are particularly evident in both flower morphology, where the primary filaments are inserted 4-5 mm above the base of the nectar chamber, and seed micro-morphology. In these specific species, the seed testa cells take on a conical shape, and the surface of the cuticle is characterized by its smooth texture.
Such unique characteristics at the seed-coat micro-morphological level prompted Doweld to propose the establishment of a new genus, Torreycactus, specifically for these plants. This proposal reflects the recognition of their distinct features that set them apart from other members within the broader Thelocactus genus.

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