P. subterranea is native to Argentina Northwest and Bolivia where the plant can spread up to 3200 m of altitude. The plant grows on the plateaus of the high Andes in grasslands between shrubs.
P. subterranea is an uncommon succulent belonging to the Cactaceae botanical family. The cactus is sometimes classified in Opuntia genus although it doesn’t resemble an Opuntia. The plant is a small geophytic cactus which grows in dense clumps. The stem is greyish-green, thin, arranged in ball-shaped tubercles and emerge from the ground for 1 cm and can form large tufts with more than 100 heads. The roots are tuberous and deep, specialized to withstand to the drought. The leaves are very small and fall off early. The areoles are absent and the bristles are inserted directly into the stem. The bristles are short yellow, flat, curved, pointed, hairy, not very dangerous and few in numbers. Blooming occurs during the summer and the blossom is borne at the apex of the plant. The flowers can take on different colors: they turn from pink to yellow to brown and rarely to white. The flowers are 2-3 cm in diameter, very show with white and hairy stamens. The flowering is diurnal and last few days. Although the plant is slow growing it tends to proliferate more than the type species both in habitat and culture.
This is a slow growing plant, easy to cultivate. The plant needs a full light sun exposure but is recommended to avoid direct sun-light in the hottest periods. The plant does not like temperatures below 5°C so it needs to be placed indoors in the coldest periods. The soil should be mixed with pumice, clay and loam to allow the drainage and prevent the root rot, the plant is prone to it indeed. Remember to use a perforating pot to drain excess water. Watering can be done regularly in Spring and Summer: during the vegetative period you can water the plant (every 7 days), checking that the soil is completely dry before watering again; in winter you should stop the watering to allow the plant to enter dormancy. If you want a faster and lush growth you can fertilize the plant once a month during the growing season with the specific fertilizers for succulents; stop fertilizing throughout the winter. If the pot starts to be too small for the plant you can repot the plant in a pot 2 cm wider. Repotting should be done early in the growing season with fresh new potting soil. Be careful to red spiders and mealy bugs.
Propagation can be done by cutting or by seed. By cutting you can make the cut during the spring and then let the cutting dry; after a few days the cut surface will dry and a callus will form, then place the cutting in a mixture of sand, soil and pumice. To increase the success of propagation you can make two or more cuttings at the same time. For cuttings it is recommended temperatures around 20 °C. By seed it is very simple to propagate the plant, it is enough to sow the seed in a sandy loam soil and keep it with a high level of humidity and at temperature of 14 C°.
It takes its name from a plateau located between Argentina and Bolivia, the place of origin of this species.
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