Spring beauty (Claytonia, Montiaceae) in Beringia: new evidence on species delineation from morphometrics and phylogenetic analysis of plastid and nuclear dna sequence data

Abstract

The genus Claytonia L. (Spring Beauty) is well known for its attractive flowers and can be found throughout the state of Alaska. Although the genus is a highly recognizable member of Alaska flora, there is much confusion over species delimitation in Claytonia. This research provides additional evidence on species delineation and sectional divisions within the genus Claytonia. I address species delineation in Claytonia from Beringia using two separate and commonly adhered to species concepts. I first look at morphological species delineation using a digital approach to traditional morphometrics. I use the program ImageJ and high-resolution digital herbarium images from the University of Alaska Museum digital database, ARCTOS, to take digital measurements and quantify morphological variation in six different species of Claytonia. I take 20 measurements on a total of 60 specimens representing the six species. I use a hierarchal cluster analysis, principle components analysis, and conditional inference tree analysis to quantify variation in specimens. My results clearly distinguish sectional divisions, but additional measurements would be required for distinguishing species level taxa. I show that digital morphological analysis helps to enhance our understanding of morphological diversity within Beringian Claytonia. My second approach seeks to clarify species limits using molecular variation. I use sequences from eight different plastid and nuclear markers (nuclear ribosomal internal transcribed spacer, trnK-matK, rps16, sqd1, at103, trnL-F intergenic spacer, trnS-trnG intergenic spacer, and ycf3-trnS intergenic spacer) to investigate molecular variation within the genus Claytonia. I also provide an estimated time of divergence for these taxa. I find that sectional divisions supported by phylogenetic analysis of molecular sequences correspond with morphological variation in Beringian Claytonia. I also find highly supported molecular evidence for a sister relationship between C. joanneana and C. sarmentosa. However, resolution of phylogenetic relationships within sect. Rhizomatosae is impaired by low genetic divergence between species indicating recent, rapid divergence. A divergence time estimate using sequence data from the genetic marker ycf3 dates the most recent common ancestor of Beringian members of sect. Rhizomatosae at 3.6 million years before present. My results showing that speciation of Beringian Claytonia has occurred within the late Pleistocene and early Holocene may explain the lack of molecular divergence and incomplete lineage sorting within this group.