About the genus
Maihueniopsis are a small genus of mound-forming opuntias predominantly from Chile and Argentina with the range extending just into Bolivia. They occupy a wide range of habitats from low-lying arid steppe and desert areas up to high-altitude Andean valleys often growing in full sun on stony hillsides.
They vary in size from the small species such as M. minuta to the much larger mounds of some of the Chilean species which can be several feet in diameter. Spines vary in shape and length from the small and sometimes almost absent spines of M. mandragora to the impressive long flattened spines of M. platyacantha.
Their flowers are typical of opuntias and vary in colour from pale greenish-yellow through varying shades of yellow to rich, deep oranges depending on the species. The flowers are generally large and showy and are often produced in succession over a few weeks.
How to grow them
Given the habitats from which Mainheniopsis originate, they are very tough plants and present few difficulties in cultivation. If kept dry in winter they are remarkably hardy and are ideal candidates for an unheated greenhouse or cold frame and the author keeps his entire collection in these conditions.
They grow well in a compost of 50% JI No.3 and 50% coarse grit. To this the Molar clay type cat litter can also be added to give a loose, open and very free draining mix. Although some species form large tap roots, over time they will grow well and look their best in wide shallow pans which suits their clumping nature. Like many clump-forming plants growth is slow to start with but this soon accelerates as each successive segment in turn produces more segments. Repot when they reach the edges of the pot. The usual caution needs to be applied when repotting opuntias as the spines are barbed and the small easily detachable clumps of glochids at their base are both barbed and an irritant.
Some of the species such as M. mandragora and M. minuta, will flower well in a 4 or 5in (10 or 13cm) pot whilst others need to be a little larger to perform well. A cold dry winter rest seems to stimulate good flowering.
If grown in an unheated greenhouse in the UK, watering can commence in mid-April and then continue until early September when the plants should be allowed to dry out and enter a winter resting state. The author only feeds his plants a couple of times a year with a low nitrogen fertiliser.
Propagation is easiest from segments detached and rooted in the same mix as for the adult plants. It is possible to raise them from seed if it can be obtained but like many opuntias germination is patchy and early growth is both slow and atypical of adult appearance.
The species most likely to be encountered in cultivation are the Argentinian ones: M. darwinii, M. glomerata, M. hickenii, M. mandragora, M. minuta, M. ovata and M. platyacantha. The Chilean species will require a little more hunting around to source plants as they are not so widely grown.
Text and photos by Mike Partridge
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