Corethrogyne is a controversial plant genus of Asteraceae given the complex and confounding variability present within the taxon. Its distribution is restricted to parts of western North America and Mexico. Corethrogyne has been subjected to frequent taxonomic revisions. Earlier, this genus was grouped with the genus Lessingia, however currently it is recognized as a separate genus Corethrogyne. According to majority of literature sources, Corethrogyne currently contains only one species, Corethrogyne filaginifolia, which has complex infraspecific variability. Due to this variability, different number of taxa have been assigned to C. filaginifolia. For example, California Native Plant Society (CNPS) recognizes two varieties which are listed as rare or endangered. Given the lack of taxonomic treatments for these taxa, conservation and management plans are difficult to devise. This study investigated the infraspecific variability within C. filaginifolia by using psbA-trnH, matK, rbcL, rpoC1, ycf5 loci of mitochondrial genome, and ITS and ETS loci of nuclear ribosomal DNA. Samples representing C. filaginifolia were collected from across California. Maximum Parsimony (MP), Maximum Likelihood (ML), and Bayesian analysis methods were to study the taxonomic relations between C. filaginifoliataxa.
Results/Conclusions
MP, ML and Bayesian analyses showed the monophyly of all Corethrogyne taxa based on DNA transitions and transversions within the ITS and ETS loci respectively. However, within this monophyletic group, four northern California populations of C. filaginifolia clustered in a single clade in phylograms generated via each of the three methods (MP and ML bootstrap values = 82 and 80 respectively, Bayes support value = 1). These northern populations are located across the coastal areas of Del Norte, Marin, and Mendocino counties. The three populations sampled across Mendocino and Del Norte counties consistently have two transitions in ITS locus and two tranversions in ETS locus. However, the fourth population from Marin County (south of Del Norte and Mendocino counties) has a single transition in ITS locus. Additionally, voucher specimens of C. filaginifolia individuals from these four populations showed morphological differences against C. filaginifolia individuals collected from southern California. We propose that the four populations constitute a separate phylogeographic taxon given their genetic and morphological differences when compared to the plants of C. filaginifolia occurring in southern California.