Molecular phylogeny and biogeography of Linanthus (Polemoniaceae)

To better understand the evolutionary history of Linanthus (Polemoniaceae) and its relatives, molecular phylogenies based on DNA sequence data from th e internal transcribed spacer (ITS) region of nrDNA and the chloroplast gen e matK were estimated using several methods. Our data suggest two separate and well-supported lineages of Linanthus in close association with two othe r genera-Leptodactylon and Phlox. These results agree with previous molecul ar systematic work on the Polemoniaceae, but do not support the traditional classification of the genus as a natural group, nor do they support the se ctional classification within the genus. With a distribution centered prima rily in western North America and a high degree of endemism in the Californ ia Floristic Province, it has been suggested by Raven and Axelrod that the origin and diversification of Linanthus and its relatives were tied to the development of a summer-dry climate in western North America. which began a round 13-15 million years ago (mya). Increased drying during the Pliocene ( 1.2-5 mya) has also been hypothesized by Axelrod to have led to an increase : In plant speciation in California and adjacent areas. Divergence times wi thin the Linanthus lineages were estimated from the ITS and matK gene trees . A log-likelihood ratio test could not reject clock-like evolution for the matK data; however, the clock was strongly rejected for the ITS data set. Although ITS molecular evolution was not clock-like, the estimated times of divergence were similar to those of the matK data set. Within both lineage s of Linanthus there seems to have been considerable diversification that h as occurred since the Pliocene.