Molecular and Morphological Variation among Populations of Pediomelum tenuiflorum (Pursh) A.N. Egan (Fabaceae) in Nebraska, USA

Individuals of Pediomelum tenuiflorum, “wild alfalfa”, from disjunct populations in Nebraska vary extensively in their overall gestalt.Those in the western and central part of the state have a very slender growth habit, with thin stems and few, small flowers; whereas,those in the southeast have a very robust growth habit with heavy-looking stems and many tightly clustered flowers. For nearly 200years, taxonomists have alternated between splitting P. tenuiflorum into two species, with the many-flowered morphotype namedP. floribundum, and lumping all the morphological variants into one species as they are now. In this study, we investigated morphologicaland molecular characters that could be used to clarify taxonomic classifications of these morphotypes. We measured 10morphological characters on 51 specimens and sequenced nearly 300,000 nucleotide characters on the Illumina platform from threecellular genomes in seven samples of Pediomelum plus an outgroup taxon. Results revealed six significantly different morphologicalcharacters but ambiguous evolutionary histories of the plastid and mitochondrial genomes in P. tenuiflorum. Our complete plastidgenomes and genes and noncoding regions of the mitochondrial genome may be used as a foundation for studying the evolutionaryhistories of these genomes. Additionally, we identified seven highly variable genomic regions in the chloroplast genome uponwhich a molecular phylogenetic investigation on an expanded set of samples from across the species’ geographic distribution canbe conducted to further define the taxonomic placements of P. tenuiflorum and P. floribundum.