Maihueniopsis
Maihueniopsis is a genus of low, cushion- or mat-forming opuntioid cacti native to the southern Andes and the cold steppes of Patagonia. Many species develop thick, sometimes tuberous roots and are among the most cold-tolerant cacti in cultivation, making them a favourite of growers who garden outdoors in temperate and even frost-prone climates.
Description
Maihueniopsis plants are members of the opuntioid group (subfamily Opuntioideae) and share the family's jointed, segmented growth. Rather than the tall pads of a prickly pear, they build up dense, low cushions or spreading mats of small, egg-shaped or club-shaped segments, each a few centimetres long. The mounds hug the ground, an adaptation that helps them shrug off wind, cold and drought in exposed habitats.
Like all opuntioids, the segments bear tufted areoles carrying glochids — the fine, barbed, easily detached bristles typical of the group — as well as true spines that range from short and stiff to long and papery depending on the species. Below ground, many species develop a swollen taproot or a cluster of large tubers that store water and carbohydrates and let the plant survive long dry, freezing winters by effectively contracting into the soil. Flowers are cup-shaped and appear at the tips of the segments, chiefly yellow and less often orange, pink or red, followed by fleshy fruits.
Distribution
The genus is centred on the high, arid country of southern South America: the Andean slopes and altiplano of Peru, Bolivia, Chile and Argentina, extending south through Patagonia. Plants typically grow in gritty, mineral soils on exposed slopes, gravel flats and steppe, often at high elevation where nights are cold and winters harsh. These conditions — bright light, sharp drainage and pronounced cold — are the key to understanding what the plants want in cultivation.
Notable species
The circumscription of Maihueniopsis has shifted over the years, and it overlaps with the related genera Cumulopuntia, Tephrocactus and Puna; some plants are found under more than one name in collections. Species and forms often seen in cultivation include:
- Maihueniopsis darwinii — a compact, mound-forming species from Patagonia, among the hardiest of all cacti.
- Maihueniopsis glomerata — dense cushions with prominent flattened, papery spines (sometimes listed under Tephrocactus or Cumulopuntia).
- Maihueniopsis ovata — small, neat egg-shaped segments forming tidy clumps.
- Maihueniopsis clavarioides — a curious species with finger- or club-like grey segments (the type of the segregate genus Puna), popular as a grafted novelty.
Cultivation
The great appeal of Maihueniopsis is cold tolerance: several species endure hard frost when kept dry, and they are prized by growers building unheated glasshouse or outdoor gravel-bed collections. The rule for winter hardiness is dryness — plants that shrug off deep frost bone-dry will rot if cold and wet together.
Grow them in a very free-draining, mostly mineral mix in full sun; weak light produces soft, drawn segments that lose the tight cushion form. Water generously through the warm growing season once the soil has dried, then keep the plants dry and cool from autumn onward. The large tubers and taproots of many species appreciate a deeper pot or an open ground bed with excellent drainage; see Watering and Repotting for general technique. Handle with care — the glochids detach at the lightest touch and are far more irritating than the spines.
Hobby and cultivar notes
Maihueniopsis is grown mostly as a collector's and hardy-cactus specialist's plant rather than for named cultivars. The slow, ground-hugging species are sometimes grafted onto a more vigorous opuntioid stock to speed them up or to display oddities like M. clavarioides at eye level, though many growers prefer them on their own roots and slightly tuberous. Because the taxonomy is unsettled, it is worth checking synonyms (Cumulopuntia, Tephrocactus, Puna) when tracking down a particular plant.
Propagation
The easiest method is division: the segments detach readily and root quickly, so a cushion can be split or a broken joint set on dry, gritty mix to callus and root, much like any offset or pad. Seed is also viable but slower and can be erratic to germinate; see Propagation - seed and Propagation - cuttings for general guidance.
See also
- Opuntia — the best-known opuntioid genus
- Tephrocactus · Cumulopuntia — closely related Andean opuntioids
- Grafting · Soil and potting mix · Watering · Propagation - offsets · Propagation - seed