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Ariocarpus trigonus (In the vicinity of Paloma, Coahuila, Mexico)
This is one of the largest species of the genusthat  can grow up to 30 cm in diameter. it is easily recognizable for the long upright tubercles that are yellow/brownish/grey/green, divergent, strongly incurved and sharp at the apices, flattened and usually twice as long as wide.

This cactus is easy to grow and gives beautiful yellow flowers from the woolly apex in the autumn.

A grafted specimen

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Scientific name:  Ariocarpus retusus subsp. trigonus (F. A. C. Weber) E. F. Anderson & Fitz

Origin:  Mexico (Tamaulipas, Nuevo Leon)

Habitat: Grows in limestone at 600-1200 m of elevation, mostly found in colonies of considerable size, the habitat length is over 400km.

Conservation status: Listed in CITES appendix 1

Synonyms:

• Anhalonium trigonum F. A. C. Weber (basionym)
  Published in: Dict. Hort. Bois. 90. 1893
• Ariocarpus trigonus (F. A. C. Weber) K. Schumann.
  Published in: Engler, Bot. Jahrb. 24:549. 1898

Description: Solitary yellowish-green globose plant, rising slightly above ground level., rounded on top Stem: 5 to 30 cm in diameter, 4 to 25 cm tall.
Tubercles:  Upright yellow/brownish grey divergent, not crowded or basally compressed, acute at the apices, flattened and smooth adaxially, not fissured, strongly incurved, 3-8cm long, 1-2.5cm broad, usually twice as long as wide;
Root: Tap root
Flowers: Cream-white to yellowish_white (occasionally with reddish mid-ribs) with a satin sheen, 3 to 5 cm in diameter up to 4 cm long .
Blooming season: They come in late autumn or early winter.

Remarks: Ariocarpus retusus ssp. trigonus is an extremely variable species, and the tubercle size and form show considerable variation, from long and thin to short and broad)
 

A young (6 years old) specimen of A. trigonus
(KMR 46 North-West of Palmillas, Tamaulipas, Mexico)

Ariocarpus retusus is an extremely variable species,. Tubercle size and shape vary widely, a terminal areole is sometimes present at the tip. The vast amount of phenotypic variation in the species has led to the erection of several variants:

• A. retusus ssp. retusus: widespread, flowers are cream or white, occasionally with reddish midveins.
• A. retusus ssp. trigonus: somewhat less widespread with long sharp tubercles  twice as long as wide. The flowers are yellow (usually), white to pinkish white.
• A. retusus v. furfuraceus: applied to plants with equilaterally triangular shaped tubercles
• A. retusus ‘furfuraceus’ var. rostratus refers to plants with a more tapered apex to the tubercle.
• A. retusus v. scapharostroides plants from the Villa Juarez region of SLP, it is characterized by erect angular tubercles, superficially reminiscent of A. scapharostrus.
• A. retusus confusus nomina nuda
• A. retusus subsp. jarmilae nomina nuda
• A. retusus subsp. horaceki nomina nuda
• A. retusus var. pectinatus nomina nuda
• A. retusus subsp. panarottoi nomina nuda
• A retusus var. minimus is a nomina nuda which has recently been applied to plants from Echido Nuncio,in San Luis Potosi.
• A. retusus f. major applied to selected cultivated plants with very broad shaped tubercles (“Tama-botan” in Japan).

Cultivation: This species is slow-growing, but certainly not as slow as some other types of cacti. It is of easy cultivation in a well drained, non-organic, free-draining soil compost, with ample water during the growing season. Use of a weak low-nitrogen fertilizer during the growing season can encourage growth. The main threat to their development is root rot. Ariocarpus should be kept dry whenever there is a threat of cold. The appearance of Ariocarpus can benefit greatly by watering the plants from the bottom. This practice will help to keep the “wool” on the top of the plant from becoming matted or discoloured. Needs light shade to full sun. Frost Tolerance: Hardy to -10° C
Propagation: It is probably the easiest species of the genus to raise from seed, but will generally take about 7-10 years to reach flowering size, occasionally grafted.

Photo of conspecific taxa, varieties, forms and cultivars of Ariocarpus retusus.

• Ariocarpus retusus
• Ariocarpus retusus forma cristata
• Ariocarpus retusus var. furfuraceus forma mostruosa
•  Ariocarpus retusus (furfuraceus) f. major (cv. TAMA BOTAN)
• Ariocarpus retusus ssp. pectinatus
• Ariocarpus retusus ssp. trigonus
• Ariocarpus confusus (  retusus/trigonus complex )

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