Phylogenetic studies of Mammillaria (Cactaceae)--insights from chloroplast sequence variation and hypothesis testing using the parametric bootstrap

The genus Mammillaria is likely the most species-rich and morphologically variable genus in the Cactaceae. There is doubt as to whether the genus is monophyletic, and past infrageneric treatments differ regarding generic circumscription. Phylogenetic questions about Mammillaria were addressed using chloroplast DNA sequence data from the rpl16 intron and the psbA-trnH intergenic spacer for 125 taxa (113 Mammillaria, 10 Coryphantha, Escobaria, Neolloydia, Pelecyphora, Ortegocactus, and two outgroup taxa from Ferocactus and Stenocactus). Parsimony analyses were conducted using various heuristic search strategies. Bayesian analyses were conducted using the F81 and F81 + I + G models of sequence evolution. Tree topologies from the parsimony and Bayesian analyses were largely congruent. Hypothesis testing was undertaken using the parametric bootstrap to test the monophyly of the genus and the taxonomic status of Mammillaria candida. Phylogenies derived from the parsimony and Bayesian analyses indicate that Mammillaria is not monophyletic and that the genus Mammilloydia (synonym Mammillaria) is embedded within a "core" group of Mammillaria species. Both these results were corroborated by the parametric bootstrap tests. The entire rpl16 intron was deleted from species in the Mammillaria crinita group.