Globose or briefly columnar cacti originating from South America. They have green or bluish stems, with numerous ribs, from seven to twenty, depending on the species; they have round areolas, which bear numerous yellowish, brown or black spines. The adult specimens can reach even considerable dimensions, with a diameter of around 20-25 cm; in summer even the youngest plants produce numerous funnel-shaped flowers, bright pink or white, which last a few days, closing up as the sun goes down, and tendentially bloom on the areoles near the apex of the plant. Some species are solitary, others, like T. leucacanthus, tend to produce numerous lateral shoots and thus to form dense groups. In late summer the adult specimens produce roundish fruits of red color, containing the seeds.
Exposure: it needs very sunny positions, exposed to the direct rays of the sun; it does not tolerate temperatures below 7-10 ° C, therefore in winter it must be kept indoors or in a temperate greenhouse and it must be kept in a very bright place. Watering: like many other cacti it does not need large amounts of water; during the vegetative period, from March to October, water regularly, leaving the substratum to dry completely between one watering and another, and avoiding water stagnation. From October to spring suspend watering to allow the plant to go into vegetative rest, if it is kept at home or in a very heated place it is good to water it at least once a month. In spring and summer, provide poor nitrogen fertilizer mixed with the water used for watering every 15-20 days. Land: prefers loose, well-drained, possibly very sandy and slightly calcareous soils; use a prepared substrate mixing peat, sand and volcanic lapillus in equal parts.
Multiplication: it takes place by seed in spring, placing the seeds in a mixture of peat and sand which must always be kept slightly moist until germination is complete; it is advisable to supply the fungicide with the first watering of the seeds, to avoid the onset of diseases in the seedbed. The species that settle can also be propagated by taking the side shoots emitted by the plants, placing them in a single container after drying the wound for a few hours. Pests and diseases: Thelocactus they are often affected by floury cochineal and red spider mite; too abundant watering or a poorly draining growing medium can cause root rot.