Mammillaria

Phylogenetics: Mammillaria is the largest genus within Cactaceae, and numerous suggestions for infrageneric entities have been proposed, often then segregated as different genera; the different taxonomic concepts were summarized by Butterworth & Wallace (2004). Although several phylogenetic studies dealing with the genus and allies have been published, there are still many uncertainties that result from insufficient phylogenetic resolution and support.
Mammillaria was studied in detail using data from the plastid rpl16 intron and psbA-trnH intergenic spacer by Butterworth & Wallace (2004), who sampled about 4/5 of the accepted species, and Bárcenas & al. (2011) for trnK/matK compiled an even more extensive sampling.
Mammillaria was also included in the phylogenetic studies of the tribe Cacteae by Butterworth & al. (2002) and Vázquez-Sánchez & al. (2013), though with much fewer species sampled.
The first sequence data already hinted to a non-monophyly of Mammillaria (Butterworth & al. 2002), yet without support. The results of Butterworth & Wallace (2004), based on a detailed sampling, again suggested polyphyly of Mammillaria. The genera Pelecyphora, Coryphantha, Escobaria, Ortegocactus, Mammilloydia and Neolloydia were found nested in a maximally supported Mammillaria s.l. clade. Bárcenas & al. (2011) did not find sufficient support a monophyletic Mammillaria, and Coryphantha (likewise polyphyletic), Ortegocactus and Escobaria were nested in different Mammillaria clades. Vázquez-Sánchez & al. (2013) found that Mammillaria and Coryphantha could be separate clades, yet Mammillaria was supported as monophyletic only in the parsimony tree (61% BS/78% JK) but not found as monophyletic by Bayesian Inference. A clade of Coryphantha incl. Neolloydia was maximally supported in the parsimony and Bayesian trees, but C. macromeris (Engelm.) Lem. fell outside that clade, suggesting that Coryphantha is likewise polyphyletic. Escobaria was found polyphyletic as well (Vázquez-Sánchez & al. 2013), but only few species have been sampled. The results of Vázquez-Sánchez & al. (2013) also did provide some insights on generic limits in the whole assemblage, as well as taxonomic changes by segregating Cochemiea from Mammillaria, and Cumarinia from Coryphantha.
Mammilloydia was found nested in Mammillaria (Butterworth & al. 2002; Butterworth & Wallace 2004; Bárcenas & al. 2011; Vázquez-Sánchez & al. 2013) and all authors argue Mammilloydia should therefore no longer be recognized at generic rank. The Mammillaria assemblage therefore remains one of the Cactaceae groups that need further detailed study. Some nodes were so far weakly supported, and final conclusions regarding the monophyly and generic limits of Mammillara must await a more extensive sampling, especially for Coryphantha and Escobaria, until firm taxonomic and nomenclatural conclusions are possible.A