Systematics and Phylogeny of the Ipomopsis aggregata Group (Polemoniaceae): Traditional and Molecular Approaches

Abstract

A system of classification of the Ipomopsis aggregata group based on traditional field and herbarium methods has been restudied recently by another group of workers using molecular systematic methods (allozymes and cpDNA). The molecular systematists have claimed that there is not a good correspondence in general between the taxonomic relationships based on allozymes and those based on morphology. In fact, the patterns of relationship indicated by morphological and by molecular methods are reasonably congruent, with one or two exceptions. Molecular evidence revealed that the taxon I. tenuituba subsp. macrosiphon was misclassified in the original system; and on the basis of this molecular and other supplementary evidence it is segregated here as a distinct species, Ipomopsis macrosiphon, comb. nov. The molecular systematists concluded from the high genetic similarities (I) between taxa that speciation is relatively recent in the I. aggregata group, but this conclusion conflicts with the phylogenetic sequence inferred from traditional lines of evidence. Reanalysis of one test case involving a pair of taxa with a high genetic similarity in allozymes indicates that the high I value is a result of recent hybridization, and is not a valid indicator of time of divergence. High I values for some other pairs of taxa may well have the same explanation. The problem of reconciling and integrating traditional and molecular systematic evidence arises frequently in other plant groups; this general problem is discussed.