Taxonomy and biogeography of Gaillardia (Asteraceae):: A phylogenetic analysis

Phylogeny reconstructions based on DNA sequences from nuclear ribosomal internal and external transcribed spacers and plastid trnT-trnF regions were used to examine the taxonomy and biogeography of North American Gaillardia (Asteraceae). Phylogenetic analyses based on maximum parsimony, maximum likelihood and Bayesian inference criteria consistently recovered several well-supported clades. Gaillardia comosa, G. gypsophila, and G. suavis, forming sect. Agassizia, were placed sister to the rest of Gaillardia, in which the two major clades correspond to sects. Gaillardia and Hollandia. Section Hollandia consists of the Gulf Coast G. aestivalis complex. Three major, well supported clades were consistently recovered in sect. Gaillardia: (1) G. multiceps and G. turneri were sister to an Intermountain clade of G. parry, G. spathulata, and G.flava; (2) a paraphyletic G. pinnatifida and G. arizonica; and (3) G. pulchella, G. aristata, G. amblyodon, G. coahuilensis, G. mexicana, G. henricksonii, and G. powellii. Dispersal-Vicariance Analysis reconstructed a Chihuahuan Desert origin for Gaillardia, an inference consistent with earlier hypotheses. Major range expansions in Gaillardia included the following: (1) eastward expansion into central Texas and along the Gulf Coast in sect. Hollandia; (2) northwestern expansion, resulting ultimately in the Intermountain clade, but including also G. multiceps and G. turneri; (3) northward expansion of the G. pinnatifida complex; (4) easterly and especially northward expansion of G. amblyodon, G. pulchella, and G. aristata; and, possibly, (5) northward expansion onto the Great Plains by G. suavis.