Reassessment of phylogenetic relationships in Clarkia sect. Sympherica.

Clarkia (Onagraceae) is a genus of 42 annual species, mostly native to California, that has served as a model for many studies of plant evolutionary biology, particularly morphological, cytological, and genetic divergence; reproductive isolation; and speciation. Section Sympherica is the largest section with eight diploid and one allotetraploid species. Species in the section have provided important evidence about the evolution of reproductive isolation (C. lingulata derived from C. biloba) and large morphological change (C. dudleyana thought to be sister to the morphologically distinct C. heterandra, recently transferred into Clarkia from the monotypic Heterogaura). Clarkia epilobioides, another diploid species in the section, was previously shown to be one parent of the allotetraploid C. delicata, the other parent being C. unguiculata from sect. Phaeostoma. Lewis and Lewis (1955) interpreted the parentage of C. delicata and other evidence of intersectional hybridization to mean that the diploid sections of the genus, though highly diverse, were closely related and should be maintained in the single genus Clarkia. Here we assess phylogenetic relationships among the species of sect. Sympherica and related species by analyzing the nucleotide sequences of PgiC1 and PgiC2, a pair of paralogous genes that encode the cytosolic isozyme of phosphoglucose isomerase (EC 5.3.1.9). The major results were the following: (1) C. unguiculata and both genomes of C. delicata are within a well-defined "Sympherica" clade; thus, C. delicata should not be considered an intersectional hybrid; (2) C. heterandra belongs in the clade and is closely related to C. unguiculata; and (3) on the evidence of PgiC1, C. dudleyana is not in the clade and is not closely related to C. heterandra.