Reproduced from the August 1996 edition of The Cactus File Magazine.

Not forgetting Aztekium ritteri By Bill Weightman

For years it reigned as the most revered of the choice Mexican cacti, but in recent times Aztekium ritteri has been somewhat overshadowed by the discovery of some exciting new plants. Bill Weightman reminds us of the charms of this painfully slow-growing species. Photography by the author.

The recent discovery and description of Aztekium hintonii has rather upstaged Aztekium ritteri, the plant that was once, for many growers, the ultimate aristocrat of the cactus family. The original Aztekium was described by Boedeker in 1928 as Echinocactus ritteri in honour of Friedrich Ritter. The following year he erected the genus Aztekium for the new species and, for more than sixty years, until the arrival on the scene of its larger relative in 1991, it was the only member.

Aztekium ritteri comes from the state of Nuevo Leon in the north east of Mexico, a region that is the home of a number of cacti that are favourites with growers. An early reference implying that it might also be found in Guatemala – Marshall and Bock 1941, and repeated in several subsequent works – is now considered to be an error. They stated that they had "received [the plant] from Guatemala", which they may very well have done, but, if so, it had almost certainly made a very roundabout journey from its home. A disjunct population at such a great distance from the only other known habitat would probably be a record for the cactus family. It appears to be restricted to a single valley in Nuevo Leon and only occurs within that valley where its rather specialised requirements are found. It favours vertical cliffs and, at a site visited in March 1996, the cliff consisted primarily of friable limestone. Elsewhere it has been reported growing on similarly steep gypsum faces.

A single-headed specimen of Aztekium ritteri, growing in cultivation

In appearance it is a very unusual plant and is unlikely to be mistaken for any other species. It is small, the plant body seldom exceeding 5cm in diameter and rather less in height. Unlike some cacti adapted to grow in very dry conditions, it does not develop a large storage root. The body is divided into about 10 low, rounded ribs and these are in turn crossed by numerous horizontal furrows. Between these true ribs are small secondary ribs, reaching about halfway up the plant body. This sculpting of the surface is rather imaginatively considered to resemble carvings of the ancient Aztek civilisation, hence the generic name. The general effect is that the plant has shrunk or been compressed causing the surface to become pleated or crumpled. The colour of the younger growth is a rather pale yellowish green, merging to grey-green on the lower, older growth. Small weak spines and wool are produced from the youngest areoles at the growing point in the centre. The older areoles form a more or less continuous line along the centre of the true ribs, but not the secondary ribs mentioned above. The flowers are small,
not exceeding about 1cm in diameter, are coloured white to pink and usually the outer petals have a darker mid-stripe. They are produced from the central wool, with up to six being open at the same time. They have, for their overall size, a rather long tube and stand clear of the plant apex. They are also reported to be fragrant although this does not appear to be always the case. Once the plant body has reached full size it slowly offsets and small clumps are commonly found.

It was gratifying to find, at the site visited, plants of all sizes, from tiny seedlings to hoary old veterans. It was noticeable that this approximately north-facing cliff carried a much larger population than the apparently very similar but south-facing site on the opposite side of the valley. There were no obvious signs of collecting, although the largest clumps did seem to be out of reach above our heads, suggesting, perhaps, that lower ones may have been removed. These near-vertical, fragile cliffs are very prone to landslips, both natural and those induced by human activities (see article by David Rushforth in a previous issue of the magazine). It would be interesting to know how long it would take for such a landslip to be re-colonized.

In cultivation, the plant's best known characteristic is its extreme slowness of growth - probably the slowest of the entire cactus family. It usually takes several years for growth to be even noticeable. In the past, when expensive, imported plants were obtainable, the rooting process was so slow that plants often dried up before establishing themselves. And raising from seed is no easy alternative. The seed is extremely fine and, although it germinates readily producing minute seedlings, nursing these along to a viable size is very difficult. Some success has been reported in grafting these tiny plants but it is not an easy procedure. In any case, grafting produces rather atypical plants which tend to be more obese and to offset much more readily than plants growing on their own roots. The offsets of grafted plants are often produced from areoles high up on the plant body rather than at ground level. This unnatural growth can be corrected to some extent by treating grafted plants harshly and under-watering them, but the result would still not deceive anybody who was familiar with the plant growing naturally. An additional problem is that grafting is not as straightforward a task as is usually the case for cacti. The plant seems to be very lacking in sap and the newly cut surfaces have a rather dry, fibrous texture, making the union with the stock less certain. Also, the ring of vascular bundles is very small and requires very careful alignment with those of the stock. Consequently, in my experience, the percentage of grafting successes is lower than with other species. I have found that trying to root offsets from grafted plants also meets with little success. So, the propagator who can produce a plant growing happily on its own roots, by whatever method, can be well pleased with his achievement.

A grafted plant of Aztekium ritteri, on which the very unusual secondary ribs, between the main ribs, are clearly visible

Ironically enough, once a specimen is established it is no trouble to keep. Provided the grower accepts that growth is painfully slow and that no attempt should be made to hasten it along, it becomes a very easy plant to manage. Its natural habitat on crumbling rock on vertical cliff faces indicates that good drainage is of paramount importance. If ever a plant warranted the use of an old-fashioned clay pot, this is it. Damaging the roots is obviously to be avoided at all costs and repotting should be carried out only when absolutely necessary. Feeding may be employed to reduce the frequency of repotting but this should be done with extreme caution so as not to stimulate too rapid growth. The plant should be dried out completely for its winter rest when it will withstand temperatures down to 4-5 degrees. It flowers freely in cultivation, usually commencing in late spring or early summer and continuing to produce the odd bloom throughout the summer months. As mentioned, in habitat the plant appears to favour north facing slopes rather than those with the sunnier aspect. Although this perhaps suggests a preference for some shading, in the comparatively dull conditions prevailing in England it seems happy enough in our version of full sunlight.

As for the other rarer Mexican cacti the book Threatened Cacti of Mexico by Anderson, Arias Montes and Taylor contains much interesting information and the attention of readers is directed to it.

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