Maihueniopsis darwinii
| Light | Bright light to full sun; tolerates strong exposure |
|---|---|
| Water | Sparingly in the growing season; keep bone dry through a cold winter rest |
| Soil | Very gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Exceptionally cold-hardy; survives hard frosts when kept dry |
| Propagation | Division of clumps and rooting of segments; also seed |
| Toxicity | Not known to be significantly toxic; the barbed glochids are the real hazard |
Maihueniopsis darwinii is a low-growing, clump-forming opuntioid cactus from the cold steppes of Patagonia in southern Argentina and Chile, and a firm favourite among growers of hardy, outdoor cacti. It builds tight mounds of small, egg- to club-shaped segments close to the ground, an adaptation to the fierce winds and freezing winters of its home, and rewards patient growers with surprisingly large, showy flowers. It belongs to the South American genus Maihueniopsis and was historically shuffled between Opuntia and Tephrocactus before settling into its current placement.
Description
Maihueniopsis darwinii forms low, spreading clumps rarely more than a few centimetres tall, made up of numerous short segments (joints) that are ovoid to club-shaped and typically only a few centimetres long. The segments are firm and dull green to grey-green, often flushing purplish or bronze under cold and drought stress. Each areole carries a small number of stiff, spreading spines together with the fine, barbed glochids characteristic of opuntioids — inconspicuous but easily lodged in skin, so the plant is best handled with care.
Flowers are large and striking relative to the small body, appearing near the tips of the segments in late spring and summer. They range through yellow, coppery-orange and occasionally pinkish tones depending on the population, opening in bright sun. In habitat the whole plant hunkers down among rocks and low vegetation, and in the driest, coldest conditions the segments shrink and pull toward the ground.
The species is variable across its wide range, and a number of regional forms and related taxa have at times been treated under or alongside it.
Distribution and habitat
The species is native to the arid and semi-arid steppe of Patagonia, spanning much of southern Argentina and adjacent parts of Chile. It grows on open, stony ground, gravel flats and rocky slopes, often fully exposed to wind, sun and cold. These are habitats with hard, dry winters and short growing seasons, and the plant's tight, ground-hugging habit is a direct response to that climate.
Because it endures genuine frost and snow in the wild, M. darwinii is one of the opuntioids most sought after by growers experimenting with hardy cacti in cold-temperate gardens.
Cultivation
Maihueniopsis darwinii is grown much like other cold-climate opuntioids: give it maximum light — full sun is ideal — and a very gritty, sharply draining mineral mix that never stays wet. Water moderately through the warm growing months once the mix has dried, and then keep it completely dry through winter. The combination of cold and damp is what kills these plants; cold on its own, when the roots are dry, is tolerated remarkably well.
This dry-winter regime is the key to its celebrated hardiness. Growers who keep it bone dry from autumn onward often overwinter it outdoors or in an unheated frame in climates that would destroy most cacti, whereas the same plant kept moist in the cold will quickly rot. In pots it appreciates a snug root run and benefits from a generous top-dressing of grit. See Watering and Repotting for general technique.
Propagation
The easiest method is vegetative: the clumps divide readily, and individual segments detach and root with little fuss on a dry, gritty surface — see Propagation — offsets and Propagation — cuttings. Allow any detached segment to callus before setting it barely into the mix, and keep it on the dry side until roots form. Seed is also possible but slower and less commonly used by hobbyists; fresh seed sown on a mineral surface and kept lightly moist and warm is the usual approach (see Propagation — seed).
Common problems
- Rot — by far the main killer, caused by moisture (especially in winter) sitting around the roots or segments; the joints go soft and discoloured.
- Glochids — the fine barbed bristles detach at the slightest touch and irritate skin; handle with folded paper, tongs or gloves.
- Etiolation — too little light makes the segments elongate and lose their compact, characterful form.
- Pests — mealybugs (white fluff in the areoles) and root mealybugs are the usual offenders under glass; see Pests and diseases.
See also
- Maihueniopsis — the genus overview
- Opuntia — a related opuntioid genus
- Soil and potting mix · Watering · Repotting · Propagation — offsets · Propagation — cuttings · Propagation — seed