Etymology -From the Greek koryphe meaning crown and anthos meaning flower.Coryphantha is a genus that consists of relatively small, globose plants that have grooved tubercles instead of ribs. Other genera are similar to Coryphantha including Mammillaria and Escobaria. In fact, most Coryphantha where at one time included in the genus Mammillaria, but they differ primarily in that Coryphantha flower from the first year growth at the apex of the plant while Mammillaria do not flower from new growth and instead flower in rings further down the plant in mostly second-year growth. Escobaria on the other hand flower from the apex as do Coryphantha and nearly all Escobaria were once included in the genus Coryphantha in past cactus taxonomy. The difference between these two is more subtle in that Coryphantha seed coats (testa) are reticulate. In other words with a net-like or crisscrossing pattern whereas Escobaria seed coats are foveolate, meaning pitted.
Geographically, Coryphantha occur in the arid regions of the Southen U.S. and Northern Mexico while Mammillaria occurs from this range to the south and Escobaria from this same area to the north. This comparative distribution being the general state, not the range without exception. Aside from the distribution of these plants, Coryphantha typically have larger, mostly yellow flowers compared with smaller more often pink flowers of the other related genera. Again this is not without exception.
In cultivation, this genus is not at all rare, but often plants exist without adequate identification. This is especially problematic because Coryphantha plants are quite variable from seedling to mature age plants. Likewise, the presence of a central spine and/or extrafloral nectaries is variable even in mature plants. In this way several plants of the same species may appear quite different based on their age or expressed traits.
In the genus Coryphantha, many species change their appearance depending on their age. In nature these slow-growers are very much formed by their microhabitats and therefore are very variable. These are the main reasons why until today more than 360 different species were described.
After extensive field-studies, the genus Coryphantha has 43 species and 11 subspecies as to R.F.Dicht & A.D.Luthy, in their comprehensive reference book, Coryphantha – Cacti of Mexico and Southern USA (2005.
As to my opinion, R.F.Dicht is the most relevant Coryphantha author nowadays. So, I use their systematics for labelling of my Coryphantha collection.
In the New Cactus Lexicon (2006) by ICSG, the species list of Coryphantha almost same with Dicht and Lüthy's names except C.recurvata ssp.canatlanensis which is not a good subspecies. But the intrageneric classification of the genus by ICSG is somewhat different.