Cacti of the Southwest

Genus Mammillaria

Genus Mammillaria Haw. Themembersofthisgenusareforthemostpartcomparative­ ly small or sometimes extremely tiny cacti. The plant stems vary in different species from depressed and almost flat to globular or sometimes even columnar in shape, and are often referred to as “heads.” In some species these remain single, while in many others they multiply from the base to become caespitose, one individual thus sometimes forming a large clump of these “heads.” In a few species the stems may branch sparingly from higher up on the stem. Each stem is entirely covered by a system of nipple-like pro­ jections called tubercles. These are usually arranged in spiral rows, but in a few cases are more loosely organized. These tu­ bercles are usually cylindrical or conical, but sometimes may have more or less quadrangular bases and sometimes are mildly keeled below. Very early the knowledge of cacti progressed to the point where it became obvious that the huge assortment of forms they present could not be left in the one catchall genus Cactus L. By the middle of the eighteenth century Miller felt it necessary to divide the lot. By using the four old names of Tournefort, he separated out many cacti into Pereskia, Opuntia, and Cereus, leaving the rest in the genus Cactus. By 1812 even this nar­ rowed genus Cactus was too broad, and Haworth abandoned it entirely, erecting five new genera out of it, one of which was Mammillaria, including all of the unjointed, tubercled cacti. Discoveries of new species continued, and as even this genus came to include a myriad of forms, the process of subdivision began all over again. Engelmann proposed two sections of the genus Mammillaria. He had section Coryphantha, which he characterized as having grooved tubercles, green fruits, and yel­ low or brown seeds, and section Eumammillaria with groove­ less tubercles, scarlet fruits, and black or blackish seeds. Lemaire very soon elevated the section Coryphantha to a separate genus. Many concurred—although not all, as for instance Berger, who left this group as a subdivision which he rechristened Eu-cory­ phantha. This was the situation, rather uneasy and not wholly satis­ factory to anybody, when Britton and Rose presented their major study, and they swept it all away by dividing the old genus Mammillaria into a whole spectrum of new and much smaller genera. Their names are in constant use and are most familiar to us today. The old section Coryphantha became the genera Coryphantha, Escobaria, Neobesseya, and others, and the old genus Mammillaria was eliminated as the rest of its forms were separated out into new genera such as Dolichothele and Neomammillaria. It seemed that the process of subdivision had been carried to its logical conclusion by this courageous leap of Britton and Rose, and almost the whole cactophile world adopted their array of new genera with surprising speed and many sighs ‘of relief. But the genera of Britton and Rose were not to go unchal­ lenged for long. They were assaulted from two directions. As early as 1931 Fosberg questioned the basis for separating Esco­ baria from Coryphantha and concluded that the two should be recombined. This was an early expression of a desire for simpli­ fication by recombination. Many people had already found the genera of Britton and Rose so hard to tell from one another that it was often more difficult to determine the genus of a specimen directly than it was to determine its species first; and some had noted that the distinguishing characteristics of these genera were not always consistently present. But at the same time the trend to still more subdivision was Turnefort -> Tournefort genus Mammillaria 111 continued by various students. J. Pinkney Hester conducted very detailed studies of the seeds of cacti, and concluded that their variations did not well uphold the alignment of Britton and Rose’s genera, but actually, if regarded as diagnostic char­ acters, would require a new realignment. As a result, in 1941, he shifted some species from one to another of these genera and erected such new genera as Escobesseya. Backeberg had already started subdividing further with his subgenera Subgymnocarpae and Neocoryphantha. Buxbaum conducted large studies of the cacti and proposed his own new subgenera, such as Pseudocoryphantha. He also proposed major theoretical schemes of cactus evolution which would appear to indicate radical new alignments of the species in this group. Thousands of words have been written concerning Buxbaum’s phylogenetic theories, but we do not need to study them here, because no one has...