Arrojadoa RHODANTHA

Arrojadoa RHODANTHA - Pink-flowered arrojadoa, Arrojadoa rhodantha.

Arrojadoa is a genus of beautiful, unpretentious plants in the cactus family (Cactaceae), popular among succulent enthusiasts. Brazilian endemics include species that grow as shrubby masses of slender cylindrical stems branching from below.

Stems of one species can reach 7 cm (2.8 in) in diameter, while those of another may be considerably more slender. These cacti can grow up to 180 cm (5.9 ft). Closely spaced spines cover the entire plant body. Beneath the spines, the cactus has small ribs.

Flowers emerge from the very apex of the plant each season, creating growth rings as the stem continues to grow from the crown, leaving a collar of spines between new and old shoots. This genus blooms with soft, tube-like pink, red, white, or yellow flowers. Flowering lasts only one or two days, after which the flower turns black and drops off.

It produces small juicy berry-like fruits of pink, purple, or red color.

Arrojadoa rhodantha has a stem reaching up to 2 m (6.6 ft) in height, branching at the base, with erect or drooping shoots reaching 2-5 cm (0.8-2.0 in) in diameter. The ribs, numbering 10-12, are low. The cephalium consists of reddish bristles and white down. The radial spines, 20 in number, are rigid, dark brown, and reach 1-3 cm (0.4-1.2 in) in length. The central spines, numbering 5-8, are also rigid and dark brown like the radials, measuring up to 3 cm (1.2 in) in length.

The flowers open in a so-called pseudocephalium - a ring-shaped or apical tuft of white wool and reddish bristles. In this species, the first pseudocephalium forms at a stem length of approximately 25 cm (9.8 in). Usually, subsequent pseudocephalia appear at a shorter distance than the first, about 16 cm (6.3 in) apart. The flowers are dark pink and nocturnal. The fruits are oval or rounded, dark red.

Arrojadoa seeds usually germinate well without any pre-sowing preparation. As an extra precaution, seeds can be soaked before sowing in a fungicide solution (used according to instructions).

Consistently high germination can be achieved after soaking the seeds in a solution of gibberellic acid GA3 at a concentration of 1,000 ppm - 1 g / 1 L (1 g / 0.26 gal) of water for 24 hours. After soaking, seeds are sown while still moist, without allowing them to dry out.

A permeable potting soil mix is prepared for sowing, for example, from 2 parts sand and 1 part leaf mold, which is preliminarily sterilized. The top layer is best made of pure sand, on which black seeds (their condition) and sprouts will be clearly visible. Generous drainage is arranged at the bottom of the sowing container.

Seeds are spread across the surface of the moistened substrate and not covered with anything on top, only pressed lightly into the soil so they do not dry out. The sowing tray is covered with glass or film and kept in partial shade at a temperature of 22-25 °C (72-77 °F). The nighttime temperature may be somewhat lower.

Sprouts appear within one to two weeks. Seedlings are very prone to rot damage, so sowing containers must be ventilated regularly immediately after germination. To avoid problems, many enthusiasts prefer to graft young seedlings onto rootstocks and later root them or regraft them. The substrate in the tray with seedlings should not be too damp; the top layer should preferably be allowed to dry briefly.

After a few weeks, the cover must be removed entirely, gradually accustoming the seedlings to dry air and direct sun. At first, seedlings are regularly watered and misted, each time increasing the "dry period" for them.

Special notes: Seed viability decreases only slightly after several years of dry storage.

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On its own roots, Arrojadoa is grown in a sunny spot with moderate watering during the growth period. High substrate and air humidity inevitably leads to plant rot, which is especially hazardous for species with tuberous roots. Good ventilation somewhat mitigates the issue, but most specialists still recommend keeping the plants grafted. Harrisia JUSBERTII, Cereus PERUVIANUS, or Trichocereus SPACHIANUS are used as rootstocks. On a graft, cacti lose a bit of their typical appearance, but they respond painlessly to excessive watering and high air humidity.

Plants are potted into a well-drained substrate, for example, a mixture of leaf mold, turf soil, coarse sand, and gravel or other filler (2:2:2:1), pH ~ 5.6. Branching species feature rapid growth and require more frequent repotting. Overwintering is dry at 12-15 °C (54-59 °F), minimum 8 °C (46 °F).

With the start of a new growing season, the shoot "breaks through" the spent pseudocephalium and soon overgrows again with a tuft of wool and bristles, preparing for subsequent flowering. Usually subsequent pseudocephalia appear at a shorter distance than the first. Over time, the cactus stems indeed come to resemble a "skunk tail", as local residents call Arrojadoa.

Flowers are usually clustered in bunches, opening during the day in most species and pollinated by birds. The flowers are tubular, 3-4.5 cm (1.2-1.8 in) long and 0.8 to 1.2 cm (0.3 to 0.5 in) in diameter, red, pink, purple, violet, yellow, white, or bicolored. The flower tube is naked. Setting fruit requires cross-pollination between flowers of different clones; sometimes it is sufficient to cross-pollinate flowers on a single plant.