Leptosiphon

Abstract: To better understand the evolutionary history of Linanthus (Polemoniaceae) and its relatives, molecular phylogenies based on DNA sequence data from the internal transcribed spacer (ITS) region of nrDNA and the chloroplast gene matK were estimated using several methods. Our data suggest two separate and well-supported lineages of Linanthus in close association with two other genera— Leptodactylon and Phlox. These results agree with previous molecular systematic work on the Polemoniaceae, but do not support the traditional classification of the genus as a natural group, nor do they support the sectional classification within the genus. With a distribution centered primarily in western North America and a high degree of endemism in the California 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 around 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 within 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 lineages of Linanthus there seems to have been considerable diversification that has occurred since the Pliocene.

Abstract: Leptosiphon Benth. (Polemoniaceae) has 40 taxa, distributed mainly in western North America, with one species in Chile. Phylogenetic studies of Polemoniaceae have consistently supported recognition of Leptosiphon as a separate genus from Linanthus, and resolved an array of taxonomic problems; however, several issues remained unclear for Leptosiphon. In those studies, sampling of Leptosiphon was incomplete, and certain species having strikingly similar floral morphologies appeared non-monophyletic, while other species groups with divergent floral morphologies formed a clade. Our analyses use greater sampling across taxa in Leptosiphon and, in addition to nrITS, the non-coding chloroplast region trnS–trnG to help resolve the genus phylogeny. These results yielded a more complete phylogeny from which to base further research on floral evolution in this group. However, much work remains to be done in resolving species level relationships. Analyses of morphological character evolution suggest that sev...

Abstract: Three hundred seventy nine species of Polemoniaceae are arranged in a phylogenetic classificat ion composed of three subfamilies, eight tribes. and 26 genera. Nomenclature of one tribe is clarified and the circumscription of several tribes differs greatly from previous classifications. Five new genera, Bryantiella, Dayia, Lathrocasis, Microgilia, and Saltugilia, are proposed. In addition, four new species are described from the genera Allophyllum, Dayia, Giliastrum, and lpomopsis. This treatment repr esents a major reclassification with 59 new combinations, and the application of several additional combinations not used in recent years .

Abstract: Phylogenetic reconstruction based on sequence variation in the internal transcribed spacer (ITS) region of rDNA was used to investigate the evolutionary dynamics of homomorphic self-incompatibility in Linanthus section Leptosiphon (Polemoniaceae), a group of annual plant species. Hand-pollination experiments revealed that five species were self-incompatible and four were self-compatible. Optimization of breeding systems onto the tree resulting from maximum-likelihood analysis, with no assumptions made about the ancestral condition, indicated that self-incom- patibility has been lost four times in this section. An alternative tree rearrangement conforming to the hypothesis of three losses of self-incompatibility did not have a significantly lower likelihood than the maximum-likelihood tree as determined by a paired-sites test, but all rearrangements resulting in fewer than three losses were statistically rejected. Linanthus bicolor, a selling species, was found to be polyphyletic, with populations from different geographic regions occurring in three well-supported clades. Morphological similarity in these distinct lineages is likely to have resulted from convergent evolution of traits associated with self-fertilization. Selection for reproductive assurance is hypoth- esized to have played an important role in the recurrent transformations from self-incompatibility to selling in this group of annual species.