Ariocarpus TRIGONUS

Ariocarpus TRIGONUS - Seven stars cactus, Living rock cactus, Ariocarpus trigonus.

Ariocarpus is a genus of semi-subterranean cacti in the family Cactaceae, comprising about a dozen species. All of them are endemic to the limestone hills of northeastern Mexico and southern Texas, where they grow on stony barren soils, exposed to harsh sunlight and prolonged droughts.

The stem is flattened, almost hidden underground; only dense fleshy tubercles shaped like triangular petals or scales protrude above the surface. Mature plants lack true ribs and spines, and dense white wool forms in the axils of tubercles and at the apex. The root system is turnip-like, massive, capable of pulling the entire plant underground during periods of drought.

Flowering occurs in late summer or autumn. Flowers are large, funnel-shaped, up to 5 cm (2 in) in diameter, emerging from dense wool at the stem apex, colored from white and cream to yellow and pinkish-purple. Seeds are small, black, ripening inside fleshy fruits hidden in the apical wool.

Ariocarpus trigonus is one of the largest species of the genus; the stem reaches 10-20 cm (3.9-7.9 in) in diameter. The triangular tubercles are elongated, acute, curved upward, up to 5 cm (2 in) long and up to 2.5 cm (1.0 in) wide, gray-green or olive, with a smooth surface.

Flowers are creamy-yellow or pale yellow, up to 5 cm (2 in) in diameter, with silky petals, appearing in autumn from dense apical wool. The species originates from the Mexican states of Nuevo Leon and Tamaulipas.

Ariocarpus seeds are small, black, ripening in fleshy berry-like fruits. Usually no pre-sowing preparation is required, but some specialists recommend cold stratification for 2-3 weeks at a temperature of 5-6 °C (41-43 °F): ariocarpus seeds often show underdevelopment of embryo tissues, and cold treatment helps them mature.

For stratification, seeds are mixed with moist sand in a ratio of 3 parts sand to 1 part seeds and placed in the refrigerator without covering with a lid.

Unlike soil for mature plants, the substrate for seedlings should be more nutritious: a mixture of leaf mold and sand or peat and sand in equal parts is suitable. The top layer about 0.5 cm (0.2 in) thick is best made from coarse sand, brick grit, or expanded clay grit. Sterilization of the substrate is mandatory; additionally, it can be drenched with a weak solution of potassium permanganate.

Sowing containers are soaked with water, seeds are slightly pressed into the surface without covering, and moistened from a spray bottle with a growth stimulant solution: SUPERthrive, HB-101, Aminozol, Epin, or Zircon. The container is covered with glass, plastic wrap, or placed in a mini-greenhouse and kept in a semi-shaded spot at a temperature of 20-25 °C (68-77 °F), preferably 18-20 °C (64-68 °F) at night.

The first sprouts appear as early as after a week, mass germination is observed over the following 10 days, while solitary seeds can emerge for up to a year. Seedlings develop relatively quickly and form 2-3 tubercles after 3-4 months. During the first months, they must be monitored carefully to prevent mold and rot: at the first signs, the sowing is opened and the substrate is completely dried before the next watering.

If development proceeds without problems, it is recommended to keep seedlings hermetically sealed for a year to a year and a half - young ariocarpuses respond very well to a moist enclosed environment at room temperature and diffused light. After this, they are gradually acclimated to dry air and pricked out into a loose, permeable substrate of leaf mold, turf soil, and sand with the addition of fine gravel or expanded clay in a 1:1:1:2 ratio, with an acidity around pH 6.

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Ariocarpus requires bright indirect lighting with a daylight period of at least 12 hours a day.

In summer, temperature does not play a significant role. In winter, it is lowered to 12-15 °C (54-59 °F), but not lower than 8 °C (46 °F) - with stronger cooling, the plant perishes.

Watering is done very sparingly, only when the substrate has dried out completely, and during the dormant period plants are not watered at all. Settled room-temperature water is used and poured directly onto the soil to avoid wetting the stem. Misting is contraindicated - it easily causes rot.

The substrate must be sandy, practically free of humus; sometimes simply coarse river sand is used. To protect against rot, charcoal and fine gravel or brick grit are added, and the surface is mulched with pebbles. A clay pot with good drainage is preferred - it presents fewer problems with excess moisture.

Fertilizer is applied a couple of times during the growing season with mineral fertilizer for cacti and succulents.

Repotting is carried out as the plant outgrows its pot and very carefully: the root system in ariocarpus is delicate. The soil is dried before repotting, and the plant itself is potted on along with the root ball.