Taxonomy of Astragalus robbinsii var. fernaldii (Fabaceae): molecular and morphological analyses support transfer to Astragalus eucosmus

Abstract

Astragalus robbinsii var. fernaldii , Fernald’s milkvetch, is a taxon of conservation concern currently due for reassessment of its provincial and federal conservation status. Restricted to a narrow region spanning Newfoundland and Labrador and Quebec, its taxonomic position with respect to two congeners, Astragalus eucosmus and Astragalus robbinsii var. minor , is poorly understood. To clarify the taxonomy of Fernald’s milkvetch, we studied variation in the ycf6–trnC and trnC–rpoB chloroplast DNA (cpDNA) spacers, generated amplified fragment length polymorphism (AFLP) genotypes, and conducted a morphometric analysis. Parsimony and Bayesian analysis of the cpDNA data distinguished A. robbinsii var. minor from A. eucosmus and the majority of Fernald's milkvetch samples; both cpDNA and AFLP analysis were highly suggestive of gene flow between taxa and populations. Morphometric analysis indicates that Fernald's milkvetch is closer to A. eucosmus than to A. robbinsii var. minor in overall form and stipe length, while pubescence was not taxonomically informative. Based on these results, the recognition of Fernald's milkvetch is unwarranted; we recommend that the taxon be transferred to A. eucosmus.