The habitat of Ariocarpus retusus is Mexico, where it can often be found growing on rocky limestone slopes amongst semi-desert vegetation. It is quite widely distributed, mainly in the states of Coahuila, Nuevo León, San Luis Potosí and Tamaulipas. Plants are normally single-headed, though they may clump with age or after damage to the main head.
They flower mainly from mid-September till well into November. The flowers are large, often with three or more open at once, and are mainly white (Fig. 1) or sometimes with very attractive pink tinges (Fig. 2). Plants can grow to be quite large, eight inches across (20mm) or more. There are many forms and varieties, some with wool at the tips or just below and some with none. Some have long tubercles, in some cases with sharp points, and some have shorter but chunky tubercles (Fig. 3). There is a much smaller variety scapharostroides (Fig 4) and a really tiny form ‘Minimus’ (Fig. 5). Both these smaller forms are shown in 2¾-inch (70mm) pots.
My fascination with Ariocarpus retusus, and with all the other (very few) species of Ariocarpus, dates back to my early teens when I started to grow them from seed, at that time (and on my budget) the only feasible way of acquiring them. I have since then always grown them and have raised more from seed every year. They were reputedly slow and difficult but over the years I have found ways of encouraging them to grow a little more quickly and discovered that they are not at all difficult.
They have fleshy tap roots and therefore all need a very open compost (not peat-based), plenty of warmth in the growing season and good light but not necessarily the sunniest position, preferring diffused light. They can then be watered weekly in hot spells and fortnightly or less in cooler weather during the growing season. From mid-October to early April they should remain dry and need only enough heat to keep them frost-free.
Their attraction to me is that they take up little space, grow sedately, are wonderfully symmetrical, have no spines but instead have lovely soft wool and breathtakingly large and colourful flowers. Indeed they are the aristocrats of the cactus family and with careful cultivation should outlive even a teenage grower!