Coryphantha RETUSA

Coryphantha RETUSA - Retuse coryphantha, Coryphantha retusa, Mammillaria.

Coryphantha is a numerous genus of globose or cylindrical succulent plants in the family Cactaceae, whose habitat extends across deserts and savannas from the USA to Mexico. The species growing in the southernmost part of Mexico are the easiest to cultivate, while those growing closer to the north of the country and in the USA are usually more difficult to grow.

Many species constantly change their appearance during the growing season. Tubercles are located on the stems of cacti; in desert species, thick spines can be observed instead of tubercles. The role of both is to retain moisture, which is scarce in drought conditions. In mature plants, a characteristic groove runs from the areole along the upper side of the tubercle, after the appearance of which flowering begins in the cacti.

Almost all species bloom regularly from summer to late autumn with numerous large yellow flowers, reaching 6 cm (2.4 in) in diameter. The first flowering can be observed in specimens older than five years. Some grow very slowly: more than ten years may pass from sowing until the time of the first flower's appearance. It may take another couple of years until the full development of spines is reached.

After flowering, juicy fruits in the form of berries appear.

Coryphantha retusa is a small gray-green species, densely covered with yellow-brown woolly spines. The stem is depressed-globose, 5-10 cm (2-4 in) in diameter, 3-8 cm (1.2-3.1 in) high, with a narrowed base and a very woolly apex. It usually grows solitary. Areoles are oblong, 4 x 2 mm (0.16 x 0.08 in) wide. Roots are fibrous.

Central spines are absent or, very rarely, 1 central spine is present. Radial spines: 6-12 (up to 15) pectinate, of which 3-4 on each side, strong awl-shaped, flattened, curved toward the body and slightly downward, the lowest ones pointing straight down, 3-5 in the upper part of the areoles are thinner needle-like. All are 14-20 mm (0.6-0.8 in) long, pale yellow/white with darker tips, later turning gray.

The flowers are dark yellow, opening from the center of the plant. It blooms profusely.

Seeds are sown on the surface of a moistened mineral mixture (sand and fine perlite), slightly pressed in, and covered with glass or film. Sowings are kept at a temperature of 22–26 °C (72–79 °F), in diffused light. Regular airing is provided.

Seedlings appear in 7–25 days. The maximum germination period can exceed 30 days. After the appearance of the first spines, pricking out into individual containers is carried out.

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Most species of Coryphantha are fairly easy to grow. The easiest way to keep them is greenhouse cultivation. However, some species, especially from southern and central Mexico, can be grown on a windowsill, as well as in garden culture, provided they are protected from rain and frost. These are very valuable plants that can adorn any collection. The happiness and pride from the success of cultivating such a gem are a worthy reward.

They are quite undemanding regarding the surrounding climate. In summer, they require plenty of light and heat, and can be watered frequently. In winter, they require rest for several months and no watering. They do not need to be kept right under glass, but in a place with plenty of light and direct sunlight.

The plants rarely get sunburned; on the contrary, they protect themselves by increasing pubescence and increasing the length and density of spines, which makes them more attractive. However, adequate air circulation and room ventilation are necessary. In winter, if the plants are hardy and the soil is completely dry, they can tolerate negative temperatures. Still, ideal temperatures range from 4 °C to 12 °C (39–54 °F).