While the opinion prevailed that Coryphantha should be treated as a genus separate from Mammillaria, authors had to deal with the question of its position within Cactaceae and to decide whether Coryphantha should be divided into smaller groups. Consequently, BRITTON & ROSE (1923) separated Escobaria and Neobesseya from Coryphantha, while BUXBAUM (1956) treated Escobaria as a separate genus and, as the first author, included the Vivipara complex in Escobaria. BENSON (1969) regarded Escobaria as a subgroup of Coryphantha because of the tubercle grooves, an opinion which persists to this day, especially in America.HUNT (1978) and TAYLOR (1978) continued the European tradition and have treated Escobaria and Coryphantha as different genera, mainly because of the testa morphology. Similarly, JOHN & RIHA (1981) treated Escobaria as a separate genus, with Neobesseya Britton & Rose being one of its subgenera.
In his thesis, Systematics of the Genus Coryphantha (Cactaceae), A. ZIMMERMAN (1985) described the genus in detail , defining 169 usable and 30 rejectable characteristics for phenetics. He used them to outline clado-grams of the tribus Cacteae and the genera Coryphantha (incl. Escobaria) und Mammil-laria.
Zimmerman derived two phylads from a group corresponding to the Erianthi (Berger) (Echinocactus Link & Otto, Homalocephala
Britton & Rose and Astrophytum Lemaire) characterised by flowers with mucronate perianth segments and axillary trichomes:
The first is characterised by convex testa cells (tuberculate seeds), the second by concave to tabular-concave testa cells (foveolate seeds).
This second group he called "Mammillaria phylad", which includes the genera Ferocac-tus Britton & Rose, Acharagma (N.P. Taylor) Glass, Coryphantha (Engelmann) Lemaire, Escobaria Britton & Rose, Ortegocactus Alexander and Mammillaria Haworth.
According to Zimmerman, this second phylad is not characterised by progressive loss of the perisperm (BUXBAUM 1956-60), but mainly by progressive development of various types of areoles.
Types of Areole Development According to ZIMMERMAN (1985)
1. The Acharagma type ("primitive type"): plants producing only non-specialised circular to elliptical areoles even in old age, producing flowers only at the tips of the areoles. Includes all taxa of the subfamilies Opuntioideae and Pereskioideae, and nearly all members of the Cactoideae except the tribus Cacteae.
2. The Ferocactus type: plants flowering from short, broad areolar grooves i.e., from the adaxial extremity of an areole which becomes longer with age.
3. The Macromeris type: like type 2, but with gradual development of narrow grooves, these never covering the whole length of the tubercles between the areole and the axil (about half the length in Coryphantha macromeris), and flowering only after the areolar grooves have attained maximum length.
4. The Escobaria type: like type 3, producing longer and longer areolar grooves, but flowering only after these have attained maximum length along the whole tubercle from the areole to the axil.
5. The Neolloydia type: with an abrupt change from short, sterile areoles to areoles having full length grooves from the areole to the axil, without a transition, with grooves getting longer. Known only for Neolloydia conoidea.
6. The Protomammillaria type: like type 5, but with a subadult stage with abaxial and adaxial meristem (like Mammillaria type), changing abruptly to complete tubercle grooves from the areole to the axil when reaching the adult stage.
7. The Ortegocactus type: like 6, but flowering is also possible before production of areolar grooves.
8. The Leuchtenbergia type: plants with axillary meristem, but which produce their flowers only at the tips of the areoles.
9. The Mammillaria type: like 7, but never make the subsequent switch to grooved tubercles at adulthood.
10. The Pachycereus type: like 1, with inter-areolar lines of trichomes in adulthood.
11. The Ariocarpus type: like 9, but without development of the abaxial tubercle part (no spine formation) or groove.
Coryphantha sp. belong to types 3,4,6 (most of the species with nectary glands) and 7 (the Ottonis sp.).
Because of the common areole types (Escobaria type, Protomammillaria type) Zimmerman, continuing the American tradition (Benson) concluded that Escobaria and Cory-phantha have to be regarded as sister groups within one and the same genus. Hence, the older name Coryphantha should prevail and Escobaria should be positioned as a subgenus, this in spite of the discrepancies concerning flowers and testa morphology. Pro-tomammillarias [Coryphantha chihuahuensis (Britton & Rose) Berger and Coryphantha henricksonii (Glass & Foster) Glass & Foster] are treated by Zimmerman as intermediate between Escobaria and Coryphantha (see Fig. 30).
However, he does not answer the question whether some of the taxa with grooved tubercles, namely the Protomammillarias and the gland-producing group of Coryphantha s.str. with Protomammillaria-areole type, might originate from a Mammillaria-like ancestor or vice versa.
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