Tephrocactus
Tephrocactus is a genus of small opuntioid cacti native to the arid highlands and lowlands of Argentina, where the plants grow as low, branching chains of loosely attached, egg- to globe-shaped segments. The genus is a firm favourite among collectors for its bizarre, often papery or flattened spines and its neat, sculptural clumping habit rather than for showy flowers.
Description
Plants in the genus Tephrocactus are made up of short, segmented stems — a series of firm, rounded or egg-shaped joints stacked and branched end to end, usually forming a low mound rather than a tall column. As with other members of the opuntioid group, each segment carries tiny barbed glochids tucked into the areoles; these detach at the slightest touch and are a genuine nuisance to remove from skin, so the plants are best handled with care.
The great appeal of the genus lies in the spines, which vary enormously between species and even between individual plants. Some carry stiff, straight needles; others are famous for long, flattened, flexible, papery spines that curl and twist like wood shavings or ribbon. Colour ranges from chalky white and grey through straw and tan to near-black. The specific epithet of several species, and the genus name itself (from the Greek for "ash-grey"), reflects the muted, dusty tones typical of these plants.
Flowers are produced at the tips of segments in the warmer months, usually white, cream, pale yellow or pink, and relatively short-lived. Many collectors' plants flower only sparingly, and the genus is grown far more for form and spination than for bloom.
Distribution
Tephrocactus is essentially an Argentine genus, centred on the arid centre and north-west of the country and extending into neighbouring high-altitude regions. Plants grow in open, gritty, well-drained ground — sandy flats, rocky slopes and montane scrub — often at considerable elevation, where they endure intense sun, sharp drainage and cold, dry winters. This background of bright light and hard, mineral soils is the key to understanding their cultivation needs.
Notable species
- Tephrocactus articulatus — the paper spine cactus, the most widely grown species, whose "papyracanthus" forms bear the celebrated flat, papery spines.
- Tephrocactus geometricus — prized for its almost perfectly spherical, blue-grey segments and short, dark spines.
- Tephrocactus alexanderi — a variable species with rounded segments and stiff, spreading spines.
- Tephrocactus molinensis — a small species with short, reddish-brown spines, restricted to the Calchaquí Valley of Salta.
- Tephrocactus weberi — a densely spined, clumping species.
- Tephrocactus aoracanthus — a robust species bearing long, stout spines.
Cultivation
Tephrocactus species are undemanding once their preference for a hard, lean life is respected. Grow them in a very free-draining, mostly mineral mix with plenty of grit or pumice, in the brightest position available — full sun suits them, and shade quickly leads to soft, elongated growth. Water only when the soil has dried right out during the active season, and keep the plants dry and cool through winter; wet, cold roots are the surest way to lose them. Many growers find that a cold, bone-dry winter rest not only prevents rot but improves both spine quality and the chance of flowering. See Watering and Repotting for general technique.
Because the segments detach so readily, handle and repot these plants gently, and beware the glochids — a pair of tongs or a folded strip of card makes moving a plant far less painful.
Propagation
Propagation could hardly be simpler: a detached segment laid on dry, gritty mineral soil will usually root within a few weeks. Allow the joint to callus for a day or two first, keep it barely moist and warm, and pot on once roots take hold. This ease of vegetative increase means most collections are built and shared through segments rather than seed, though the species can also be raised from seed with patience. See Propagation — offsets and Propagation — cuttings for a full walkthrough.
Hobby and cultivar notes
Collector interest focuses heavily on spine form, and certain heavily papery-spined or particularly geometric clones are passed around under informal names and field numbers. Slow-growing or difficult clones — and choice seedlings — are sometimes grafted onto a vigorous opuntioid rootstock to speed them along, though most Tephrocactus grow perfectly well on their own roots given sun and sharp drainage. The genus is closely allied to other South American opuntioids such as Maihueniopsis and Cumulopuntia, and older literature and labels sometimes shuffle species between these groups.
Common problems
- Rot — almost always from overwatering, a slow-draining mix, or cold wet winters; affected segments soften and discolour.
- Etiolation — too little light produces pale, stretched, weakly spined segments that lose the compact form.
- Pests — mealybugs (white fluff in the areoles) and red spider mites are the usual offenders; see Pests and diseases.
See also
- Maihueniopsis · Cumulopuntia — closely related opuntioid genera
- Grafting · Soil and potting mix · Watering · Propagation — offsets · Propagation — cuttings