Phylogenetic perspectives on diversification, biogeography, and floral evolution of Collinsia and Tonella (Plantaginaceae).
Collinsia was the subject of classic biosystematic studies by Garber and colleagues and is increasingly investigated to address major evolutionary questions. Lack of phylogenetic data from more than one gene region and one taxonomic exemplar has left relationships, diversity, and phytogeography of Collinsia in question and has limited understanding of its diversification. Phylogenetic analyses representing 179 populations of Collinsia and closely related Tonella were conducted based on DNA sequences of nuclear ribosomal transcribed spacers, the single-copy nuclear gene CYCLOIDEA-1, and part of the chloroplast matK/trnK intron region to reexamine systematic hypotheses and extend understanding of the importance of floral characters, chromosome evolution, interfertility, crossability, hybridization, edaphic factors, and ecogeographic barriers to diversification in the group. Informal "sections" of Collinsia are artificial, although pedicel length and other traditional deep-level taxonomic characters are more conservative evolutionarily than flower size. Evolutionary loss of crossability and interfertility in Collinsia appears to be largely a byproduct of divergence. Although most taxa appear to have arisen by divergent evolution, multiple lines of evidence indicate a homoploid hybrid constitution of C. tinctoria, possibly explaining an occurrence of convergent chromosome evolution. Phylogeographic and cryptic diversity is extensive. Diversity in Collinsia is greater than previously documented. Recently divergent lineages are often associated with distinct habitat (including soil) and geographic factors, different flower sizes, and contrasting chromosomal arrangements. Evidence for a hybrid constitution of diploid C. tinctoria is consistent with lack of strong intersterility barriers between closely related taxa.