Gymnocalycium ASTERIUM

Gymnocalycium ASTERIUM - Starry chin cactus, Gymnocalycium Asterium.

Gymnocalycium is a genus of plants in the cactus family (Cactaceae), comprising about 70 species widely distributed across South America, especially in Argentina, Brazil, Paraguay, Uruguay, and Bolivia at elevations of 800-3000 m (2625-9843 ft) above sea level, on granite and clay soils.

Gymnocalyciums are valued for the elegant outlines of their stems, usually globose and flattened, with a diameter of 4-15 cm (1.6-5.9 in), with height being roughly half of the diameter. The primary stem coloration varies from grayish-green to brownish-green, sometimes with an almost gray or almost brown tint. Some cultivars feature unusual red or yellow stems lacking chlorophyll; such plants are capable of developing only in a grafted state. The stems are typically distinctly ribbed, with tubercles situated along the ribs. The spines are moderately stiff, often recurved.

The plants are prized for their showy flowering. The flowers are funnelform, with a short tube, developing from areoles at the stem apex and opening during the day. Unlike most other cacti, flower tubes in members of this genus lack bristles and hairs and are covered with smooth scales. Coloration varies from white and pink to red, yellow, greenish, or brownish-yellow. The fruits are oblong, juicy or dry, containing large black seeds with a texture characteristic of the genus.

Gymnocalycium asterium has a regular round shape, 7 to 10 cm (2.8-3.9 in) in diameter. The number of ribs is 7 to 11; they are distinctly divided by transverse grooves into tubercles. Compared to other species, the ribs are fairly flat. The number of spines per areole is 3 to 5; they point downward and sideways, initially brown, turning gray with time. The spines are appressed to the stem, which is very convenient when working with the plants.

Epidermal coloration ranges from dark gray-brown to yellowish-green (olive). Over a fairly prolonged period, the plant's stem remains solitary; later, offsets may begin to appear. The flowers have a diameter of up to 4.5 cm (1.8 in) and a length of up to 6.5 cm (2.6 in). Petals are light cream (reddish-brown at the base). Blooming time is late spring to summer, with a single flower lasting about 12 days. In overcast weather, the flowers remain almost completely closed. Stamens are numerous.

Seeds are sown on the surface of a moist substrate with a pH of around 6.5. The sowings are covered with a lid, and ventilation is provided. The germination temperature is 22-26 °C (72-79 °F).

Seedlings appear in 7-15 days. The maximum germination period is up to 25 days. Pricking out is carried out when the first spines appear. Young seedlings develop quickly and tolerate transplanting well.

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It is placed on south- or east-facing windows with access to bright indirect light. In spring and summer, some direct sunlight is permissible. Regular ventilation is desirable, especially in hot weather.

Temperature in summer is maintained at 22-28 °C (72-82 °F). In winter - 8-12 °C (46-54 °F) during complete dormancy. Watering is carried out moderately, after complete drying of the substrate. In winter, watering is stopped completely.

A loose mineral substrate is used with the addition of leaf mold, sand, and brick chips. Repotting is carried out in spring if necessary. Good drainage is mandatory.

During the growth period, mineral fertilizing is applied once every 3-4 weeks. Low-nitrogen fertilizers for cacti are used. In autumn and winter, fertilizers are not applied.

Formative pruning is not required. Propagation is carried out by seed. The formation of offsets is occasionally possible in old plants. Flowering begins in the 3rd to 4th year if dormancy conditions are respected.