Coreopsis sect. Pseudoagarista (Asteraceae: Coreopsideae): Molecular phylogeny, chromosome numbers, and comments on taxonomy and distribution

Abstract Coreopsis (Asteraceae) sect. Pseudoagarista is the largest section in the genus. It is disjunct between the high mountains of Mexico and high elevations in the Andes. Most species in the section are similar in floral and fruit characters, and are distinguished primarily by leaf characters. Despite the morphological similarity among all species, the monophyly of the section has been called into question by molecular data. Prior studies of tribe Coreopsideae have been equivocal with, cpDNA markers indicating monophyly but nrDNA ITS sequences have not resolved the section as monophyletic. Expanded cpDNA and nrDNA ITS datasets, and statistical (i.e., AU) tests of the ITS and cpDNA topologies provide support that sect. Pseudoagarista is not monophyletic. Both data partitions strongly support the Mexican and South American subclades as monophyletic. The low cpDNA sequence variation within each subclade provides no resolution, and thus patterns of evolution within each were examined using a phylogenetic framework estimated from ITS data. Sequences from ITS fail to provide high resolution of relationships among South American species, a likely result of a recent, rapid radiation, as is known in other Andean lineages. Divergence among species is generally higher in the Mexican species, resulting in better resolution of phylogenetic relationships compared to South American species. Three ploidy levels (diploid, tetraploid, hexaploid) are known in species from South America, and diploids and tetraploids have been documented in Mexico. Multiple origins of polyploidy are indicated for both geographic areas.