by Bruce Brethauer
The genus of mammillaria is one of the largest of the cactus family: at one time over 500 species had been recognized, but in recent years, many of these species became subsumed as varieties of other species, so that today, the number of recognized species has been reduced to just over 170 (some authorities suggest a somewhat larger number - to over 200 or so species in some lists). The genus is one of the most advanced of all cacti, with its distinctive cylindrical, conic or pyramidal shaped tubercles1, which are produced in spirals on the plant's stems. These un-grooved tubercles, are the distinguishing trait of Mammillarias setting them apart from species of Escobaria and Coryphantha, which look very similar, but which produce a groove on the upper surface of their tubercles. Mammillarias are also known for their dimorphic areoles, in which one type of areole (at the summit of the tubercle) produces spines, and a second type of areole (produced at the base of the tubercle), produces flowers, branches, and (sometimes) wool or bristles. In virtually all other cactus genera (Escobaria and Coryphantha are also exceptions), there is only one type of areole - producing spines, branches, flowers, etc. While there is a fair degree of diversity within the genus Mammillaria, (differences in the size and shape of tubercles, spines, which may be straight, curved or hooked, the size and color of flowers, etc), there is also a remarkable degree of uniformity within the genus, such that once a person knows to look for the distinctive tubercles, they can practically identify a Mammillaria at a glance thereafter. Most plants are rather small; they range in size from tiny plants barely more than an inch tall, to taller, columnar plants growing to nearly 2 feet in height. Many species typically remain solitary, while others readily cluster from the base, eventually producing large mounds, sometimes containing over 100 heads, and measuring to as much as a few feet or more in diameter. While this is not a distinguishing trait (many other types of cacti produce similar spines) there are a good number of Mammillaria species which produces hooked spines, so that many of them bear the common name, "the fish-hook cactus"
While most species produce rather small flowers (the largest flowers in the genus barely approach 2 inches across, and in most species are considerably smaller), the flowers of most plants are brightly colored, and are produced in good numbers in ring-shaped clusters on the stems, so that the total effect can be quite striking. Many growers are particularly struck by the beautiful, geometric arrangement of the tubercles: some authorities see in this arrangement, natural examples of the Fibonacci number: in nature, this sequence of numbers results in very distinctive patterns: other examples of the Fibonacci number can be found in pinecones, pineapples, sunflowers, and the shell of the chambered nautilus. While it is not necessarily unique to the species of mammillaria, there are a good number of mammillaria species which branch dichotomously, in which the primary stem gradually divides into 2: when seen from above, these plants take on a distinctively "owl eyed" appearance.
The species of Mammillaria range from the Southwestern United States through Mexico and into Venezuela, Guatemala, Honduras, Columbia and the islands of the Caribbean, but overwhelmingly, the area of its greatest diversity lies within Mexico. The genus is very popular with cactus enthusiasts, and many growers have specialized in this genus alone, growing little else. Most of the Mamillaria species are miniature plants, suitable for small pots and dish gardens: even the largest species could be maintained (at least for a time) in a relatively small pot. Many species are easy to grow, and are perfect plants for novice growers. As a rule, if you have good success in growing one species, then you should have little difficulty in growing many others. There are of course a number of species which require special attention to soil types, watering regimens and other factors, which are better suited to experienced growers, but these are the exceptions to the rule - most Mammillaria species which are offered for sale in the cactus selections of nurseries are quite easy to grow if you can provide a few basic requirements.
The featured plant is one which had been given to me about 16 years ago by my close friend Anne (we will be celebrating our 14th wedding anniversary this year). 16 years ago, it was a smallish plant with a single, nearly globular stem that fit comfortably in a 4 inch pot. With the passing years, this stem grew taller and wider, and eventually began to produce branches from the base, and along the length of the primary stem, ultimately growing into a nice multi-stemmed cluster ( I believe that there are a total of 16 heads on this plant today); it now fits nicely in a 12 inch bowl. Over the years, I have pampered it, neglected it, and everything in-between. No matter what I do, it persists, and often thrives. Every spring and summer, I move my plant outdoors, gradually exposing it to increasingly brighter sites until it is in the brightest portion of my garden where it benefits from exposure to daylight and hot summer temperatures. It responds very well when given the conditions which I outline in my General Cactus Care guidelines. As long as I can remember, it has been a reliable bloomer, invariably flowering within about 4 to 8 weeks of being moved outdoors, and it frequently flowers sporadically at other times of the year as well. It produces a good amount of wool on new growth at the apex of the stem, and a bit further down on the stem as it begins to produce its flower buds. The wool is a temporary feature, and is usually lost within several months to abut 2 years. Each areole produces about 4 spreading central spines which are white and tipped in dark brown to black, there are many short, white, hair-like radial spines, and the flowers are small ( about 1/4 to 3/8 inch), and are bright magenta in color, with 3 or 4 magenta stigma lobes. The name of the species has been a bit of a question over the years - the plant was never properly identified, and while it bears a similarity to several species - it does not fit perfectly within any species or variety. Mammillaria albilanata v tegelbergiana is the closest thing that I could find to this plant, but even so, this variety is not noted for producing good sized clusters - it typically produces a single, un-branched stem - and only occasionally will produce offsets. Of course, I cannot rule out the possibility (or the likelihood) that this is a hybrid plant - in commercial greenhouses, it is often difficult to keep the "bloodlines" pure. Whatever its name, this has proven to be an attractive, reliable, and forgiving plant - tolerating a wide range of growing conditions, soils, and watering regimens. I must admit that I have only grown a few types of mammillaria over the years, but if this plant is typical of the temperament of its many relatives, I can understand their popularity.