Cleistocactus
Cleistocactus is a genus of slender, columnar cacti from South America, best known for the vivid red, orange or pink tubular flowers that scarcely open — the buds barely part their petals, so the blooms stay looking like tightly closed torpedoes even at their peak. The genus name comes from the Greek kleistos, "closed", a nod to those famously secretive flowers. Most species are fast-growing, densely spined columns that clump readily, making them among the more forgiving and rewarding columnar cacti for a collection.
Description
Cleistocactus plants are typically erect to sprawling columns, slim in girth compared with their length, and clothed in many low ribs bearing closely set areoles. The spines are usually fine and numerous, ranging from bristly and hair-like to stiff and needle-like, and in many species they clothe the stem so densely that the green body is almost hidden beneath a silvery or golden sheath. Older plants branch from the base to form clumps, and some species lean or trail rather than standing fully upright.
The flowers are the genus's signature feature. They are narrow, tubular and often slightly S-curved, in intense shades of red, orange, coral or magenta, and they open only a fraction — the perianth barely spreads at the mouth, so the bloom appears permanently half-closed. This shape, combined with the bright colour, is an adaptation to hummingbird pollination in habitat. Flowering can be prolific on a mature plant, with blooms emerging along the upper flanks of the stems over a long season. The fruits are small, rounded berries.
Distribution
The genus is native to South America, centred on the Andean regions of Bolivia, Peru, Argentina and neighbouring countries. Plants grow on rocky slopes, in dry valleys and among scrub, often at moderate to high elevation where days are warm and nights cool. Some populations experience a genuine seasonal rhythm of summer rain and a dry, cooler winter, which shapes how the plants are best grown in cultivation.
Notable species
- Cleistocactus strausii — the silver torch, perhaps the most widely grown species, forming tall columns densely covered in white bristles and bearing deep red flowers.
- Cleistocactus winteri — the golden rat tail, a trailing, softly golden-spined species often grown in hanging pots for its cascading stems and salmon-orange blooms. (Sometimes treated under Hildewintera or Borzicactus.)
- Cleistocactus samaipatanus — a clumping species with bright scarlet flowers, sometimes listed under Borzicactus.
- Cleistocactus baumannii — the scarlet bugler, with slender stems and striking orange-red curved flowers.
Cultivation
Cleistocactus are among the easier columnar cacti to grow well. Give them a bright position with plenty of sun, which keeps growth compact and encourages the dense spination and flowering the genus is prized for. Pot in a free-draining, mostly mineral mix and water generously through the warm growing season, allowing the soil to dry between waterings; see Watering for general technique. In winter keep the plants cooler and largely dry, which both prevents rot and helps trigger the following season's flowers.
These are relatively vigorous, thirsty cacti by cactus standards, and they respond to regular feeding and repotting with fast growth — a young silver torch can gain noticeable height each year. Most species tolerate a light frost if bone dry, but they are safest kept above freezing. Trailing species such as C. winteri are well suited to hanging containers where their stems can spill over the edge. See Repotting for potting-on advice.
Propagation
Propagation is straightforward. Stem cuttings root readily: sever a length of stem, allow the cut to callus for several days to a couple of weeks, then set it on a barely moist mineral mix until roots form. Clumping species can also be divided by separating rooted offsets from the base. The genus grows easily from seed as well, though seed-grown plants take longer to reach flowering size than rooted cuttings. See Pests and diseases for problems to watch for.
Hobby and cultivar notes
Cleistocactus is popular both as an ornamental column and as a subject for the windowsill or greenhouse collector who wants reliable flowers. The silver torch in particular is a nursery staple and a common "gateway" columnar cactus for beginners. A few crested (monstrose) and variegated forms circulate among collectors; as with most such novelties they tend to grow more slowly and appreciate slightly more shade and careful watering than the normal form. The genus also hybridises within itself and with related genera, and taxonomic boundaries with Borzicactus and allied groups have shifted over time, so some plants are sold under more than one name.
See also
- Cleistocactus strausii · Cleistocactus winteri — popular species
- Borzicactus — a related genus into which some Cleistocactus have been placed
- Soil and potting mix · Watering · Propagation — cuttings · Propagation — offsets · Repotting · Pests and diseases