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Genus Epithelantha (Weber) B. & R. Although it is developed into a number of forms in Mexico, there seems to be but one distinct species of this genus in the United States. It is a very small but unique cactus. The whole stem of this cactus is covered with very many, very tiny tubercles -apparently the smallest tubercles of any U.S. cactus. Hiding these almost entirely from view are very many tiny spines. The growing tip of the stem is in the form of a rather distinct depression which is filled with a great deal of hairlike wool and covered over by the converging, later deciduous tips of the longer spines. This makes it very difficult to observe the formation of the tubercles, areoles, and flowers, but the way these are formed has assumed much importance and has been studied very closely. This is because taxonomically almost everything hinges upon them. Originally Engelmann described this cactus as Mammillaria micromeris. In most of its characters it is a perfectly good Mammillaria. Later, however, something unusual was noticed about the cactus. It produces its flower not in the axil of the tubercle but at the top of it. Mammillarias otherwise produce their flowers from halfway down the dorsal side of the tubercles to deep in the axils. When this was noticed, it was assumed that the flower was produced from within a single, unlengthening, monomorphic areole on the tip of the tubercle . This is the situation in the Echinocacti. Because of this difference, Weber seemed unable to come to a real conclusion about this cactus, listing it once as a Mammillaria, once as Echinocactus micromeris, but also coining a new name, Epithelantha, for it. He apparently did not officially describe this latter as the name of a new genus, however. Britton and Rose then took the name Epithelantha and applied it to a new and separate genus. This genus, because of the supposed production of the flower from within the spine areole, has usually been placed in the subtribe Echinocactanae , although its other features, such as the naked fruits and lack of ribs, seem to point more toward the Mammillarias. Recently Dr. Norman H. Boke has done most thorough studies of cactus anatomy and development, and examined this species very carefully. In the course of his studies he has discovered that this cactus does not produce its flower from within a monomorphic spine areole after all. The blossom is, in fact, produced after a division of the meristem into a determinate spinous portion and a separate, indeterminate floral or vegetative meristem. This gives essentially a dimorphic areole, very different from those of the Echinocacti . It is actually more removed from the Echinocactus arrangement than is that of the many Mammillarias often set apart as Coryphanthas because they usually have monomorphic areoles elongating toward the axils instead of dimorphic areoles. The situation in this cactus can be interpreted genus Epithelantha 153 as good dimorphic Mammillarian areoles in which the floral meristems merely remain at the tops of the tubercles. Boke notes Moran’s remark that for many years no one has linked Epithelantha to Mammillaria, but Boke’s conclusion is that a strong case for doing just this can be built. This possibility is very attractive, since the cactus is in so many ways a better Mammillaria than many of the Mammillarias themselves. It does seem that the work of Boke has made it impossible to classify it any longer with the Echinocacti and that it points it toward the Mammillarias. Yet the fact remains that its flower is produced at the top of the tubercle, which is a trait not found in other members of that genus, and this difference in itself may he justification for keeping the cactus separate from the genus Mammillaria. As a separate genus based upon this cactus, Epithelantha seems, like Lophophora and Ariocarpus, to fall somewhere between the two major genera , Echinocactus and Mammillaria. It is worth noting in this connection that the Epithelanthas possess alkaloids similar to those of Lophophora and Ariocarpus, which seems to link them in some way. I, therefore, leave this genus in this difficult middle area. Buxbaum has made elaborate schemes in attempting to relate these plants phylogenetically , but others have pointed out that entirely different schemes could be devised which would appear just as logical as his, if different assumptions were made to start with. I am not primarily interested here in such phylogenetic schemes, so I merely list this as a...

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