The genus Rebutia has about sixty species of cacti, originating in South America; in this genus, in recent decades, other genera have been merged, such as Sulcorebutia, Mediolobivia, Weingartia, Aylostera, spegazzinia, Mediorebutia and others. These are generally small plants, widespread in most of Argentina and Bolivia, generally in mountainous or hilly areas. They develop a globular body, which in most species tends to shrink, producing numerous basal shoots, giving rise to small patches of plants over time. The stem is covered with tubercles, covered with thorns, often arranged in a spiral, which sometimes form a sort of depression on the apex of the plants. The thorns of Rebutia they are thin, and give the plants the appearance of small thorny balls; there are obviously some exceptions; for example, Rebutia canigueralii is characterized by very small spines, generally arranged like a comb, and oriented downwards.
The flowers of Rebutia they bloom in summer, and generally, if the plants are grown in a congruous way, the flowering is quite abundant, with decidedly large flowers, of varied color (rarely white), which bloom from the apex of the tubercles placed in the lower part of the stem.
These plants were once divided into different genera, this is because they develop in various areas of South America, thus showing different cultivation needs; depending on the altitude they live in nature, or the humidity of the area in which they live, rebutias have different needs. Generally speaking, rebutias are plants that need a very well drained soil, as their roots are very delicate and tend to be affected with great ease by any type of root rot. Watering is provided only in spring and summer, always waiting for the soil to dry perfectly between two waterings, so even in summer, it is watered only every 3-4 days. They prefer very bright positions, but do not like too many hours of direct sunlight; they are therefore positioned in partial shade, especially in the hottest period of the year. In winter instead they can be left exposed to sunlight for a few more hours; during the cold months, most rebutias can be left outdoors, in places with temperatures that can go down to -10 ° C, but in dry weather. In general, those who cultivate rebutias keep them, in the cold season, sheltered in a cold greenhouse, or under a canopy, so that they are exposed to winter temperatures, but not to rainfall. Some species, especially those that once belonged to the genus sulcorebutia, prefer temperatures above -5 ° C, therefore they are preserved in positions sheltered from intense frost. If grown in the warm even in winter, for example in the apartment, they tend to stop flowering over time.
Land and repotting
The rebutias need a very well drained soil, consisting mainly of gravel, or sand, or pumice stone, mixed with a little slightly acid soil; the root seems to be more delicate than the plant, together with the basal part of the stem; to prevent the moist soil from favoring the onset of mold or fungus, generally after placing the seedlings in pots, the surface is covered with a thin layer of coarse gravel. Most species of rebutia have very slow growth, and therefore plants usually do not require frequent repotting; we intervene every 4-5 years, replacing the vase with a slightly larger container, and being careful not to damage the root bread during the transplant operation. In the nursery we often find rebuttias grafted onto the stems of other cacti, which give the plants greater vigor, faster development, and greater resistance to soil moisture. Unfortunately, these grafts are done in a very precise way, and so it happens to notice this "cheating" only at the time of repotting. If we find rebuttons of the smallest species in the nursery, at very low prices, we ask the trader directly if it is a graft, as it takes years to get a seed plant, and the division of the heads of plants often leads to death of some of the specimens.
The recognition of cacti
The cactaceae are a genus that counts innumerable genera and species, it was Linnaeus who gave the name to the first known cactaceae, although it could have contact only with some species, probably mammillaria. So until a few centuries ago, all the globose plants, bearing thorns, were called cactus, from the Greek, Kaktos, which referred to thorny plants. Over the decades, dozens of species of cacti were discovered and cataloged, which were divided into various genera. The cacti are succulent plants, originating from the American continent, and develop in places characterized by dry seasons, or by a perpetually arid climate. Contrary to popular belief, cacti are not used to living always dry, each of them in nature enjoys at least one wet season, of different duration depending on the place of origin. Some plants are widespread in mountainous areas, even at high altitudes, while others originate from decidedly desert or semi-desert areas.
Only one species of cactacea is widespread in nature even in africa, it is rhipsalis baccifera; many species have by now become naturalized in most of the globe, as is the case with opuntia, which is considered by many to be a Mediterranean plant.
The study of systematics in recent decades has made a noticeable qualitative leap; until a few decades ago the systematics of flowers was based on the methodology of Linnaeus (more or less), that is, scholars grouped into plants the plants that showed homogeneous morphological characters. Nowadays, technology has greatly changed this type of approach; today the system is based on phylogeny, or two plants, to belong to the same genus, they must not simply have flowers of similar shape, or a similar development of leaves or stem, but must have a similar DNA, following the phylogeny, or a kinship evolutionary. Clearly the systematic organization of all the plants has not yet been done following the study of DNA, but many steps have been taken, and for this reason we happen to see plants that "change name", being moved from one genus to another , with which they have greater phylogenetic affinity.
Sulcorebutia by Bruno Bonvecchio (bonvi)
The Sulcorebutia, now included in the genus Rebutia, are mountain plants, growing in the Andes
Bolivian at high altitudes, between 2100 and 3900 meters.
The soil on which they grow is formed by basaltic rocks and humus. The temperature in nature is very cool, around 20 ° C, and in winter in certain localities it can go down a few degrees below 0.
From this it can be deduced that the Sulcorebutia do not like torrid temperatures like the desert cacti.
The greatest difficulty in cultivation is precisely the high temperatures, so in the height of summer, if too hot and muggy, it is better to reserve them a very airy place, perhaps in the morning sun, or with sun filtered through an opaque plastic cover; in nature, while loving the full sun, the sun's rays are often filtered by the numerous clouds.
As for watering, already in the month of March-April if the temperatures allow it can be provided with some light spraying or watering, otherwise wait for the first signs of vegetative awakening that manifests itself with the appearance of the buds (small red dots) for then increase to bring the plants to a progressive swelling.
In summer they should be watered about every 10 days, letting the compost dry well between one
watering and the other. At the end of August when the temperatures drop and the rains cool the air, you notice the greatest growth, the plants grow by developing shoots and new thorns.
The month of flowering for plants grown outdoors is usually around the end of May and beginning of June, even earlier if placed in greenhouses.
The soil should be very drained, a good soil is composed of a part of lapillus, one of
pumice, one of zeolite and one of sphagnum peat or blonde peat. You can use sand or quartz to cover the last layer around the plant's collar. The ph should be 6 -7.
As far as acidity and fertilization are concerned, we must not exaggerate as they produce plants
very unnatural, very swollen with elongated bodies and slender thorns, they are more easily attacked by fungal pathogens.
The pots for the species with napiform root must be deep enough to contain the large root and of adequate size to the plant.
The most common parasites are the cochineal and the red spider mite; as far as fungal diseases are concerned, it is better to prevent spraying with a copper-based product.
The propagation is carried out by sowing in the same year, as the seeds soon lose the
germination, at a temperature between 20 and 24 ° C. To obtain seeds, it is necessary to have two different clones, since Sulcorebutia are self-sterile.
Another propagation technique is for suckers. The latter is the safest way to get equal individuals to the parent since the sowing often gives variability. The best time for sucker propagation is immediately after flowering, remove the sucker, let it dry for a few days and place it on damp sand in the shade until the rootlets are sprouting.
In autumn, reduce watering until it stops altogether in October; the plants go into winter rest so they must be prepared to spend the totally dry winter months. Store the plants in a cold or slightly heated greenhouse, fresh and bright rooms with temperatures of a few degrees above 0 are also fine. In cold greenhouses they can tolerate even slight frosts with low environmental humidity and dry soil. Let yourself be tempted by the purchase of a Sulcorebutia, these dwarf plants will surprise you by giving you splendid blooms in bright magenta, yellow, red, purple, two-tone colors and be more amazed if they are white ... You will have an authentic rarity!
CLASSIFICATION Sulcorebutia, being a fairly recent genus, are in continuous study; many have not yet been described, so there will be many plants with no name of the species with only the field number; every year new species and varieties are described.
The photos published in this article are kindly granted by Mr. Bruno Bonvecchio, and depict the plants of his splendid collection