Determining the Taxonomic Status of Astragalus cusickii var packardiae using Molecular Phylogenetic Methods, Final Report

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Abstract:

Astragalus cusickii comprises 4 infraspecific taxa, vars. cusickii, flexilipes, packardiae and sterilis. All four varieties are found in Idaho with vars. packardiae and sterilis both occupying a limited geographic range and with smaller numbers of individuals - thus they are taxa of concern for conservation efforts. The other two varieties are more widespread and var. flexilipes is only weakly differentiated from the type variety based on morphology. Two of these varieties are of conservation concern, and both of (varieties sterilis and packardiae) occur in areas where soils and climate are different from where the type variety is found. It is possible that the morphological variation that has been the basis for the recognition of these varieties may be the result of phenotypic plasticity in response to the environment and thus the recognition of these taxa may not be merited. In contrast, the isolated areas where varieties packardiae and sterilis are found may have resulted in limited or no gene flow outside of these populations and resulted in morphologically and genetically distinct populations that could potentially be recognized at the level of species. <br> There is support for the monophyly of varieties sterilis, and packardiae based on phylogenetic methods and the monophyly of these two taxa are supported with additional analyses of the molecular data. Varieties cusickii and flexilipes are not reciprocally monophyletic, and although together were recovered as monophyletic in all analyses, they are not strong supported as such. Whether these three clades comprise a single monophyletic species or not remains at some level ambiguous. Methods such as the genealogical sorting index do not reject a monophyletic A. cusickii, but a model that treats the three as distinct receives greater support. In part this stems from the low resolving power of the DNA regions used here. The data provide good support for monophyletic taxa throughout, but relationships among these taxa are poor throughout as well. There are few clades that receive support across the entirety of the tree, implying that the low resolution and support of relationships among species is not unique to A. cusickii. It is therefore our suggestion that varieties packardiae and sterilis be elevated to species rankings and that no further taxonomic change with regard to var. flexilipes be made at the present time.

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Reference Code: U15ZIM01IDUS <br>

Full Citation: Zimmers, J., J.F. Smith. 2015. Determining the Taxonomic Status of Astragalus cusickii var packardiae using Molecular Phylogenetic Methods, Final Report. Boise State University, Boise, Idaho. 5 pp. <br>

Location: ELECTRONIC FILE - BOTANY: MULTIPLE SPECIES <br>

Keywords: Astragalus cusickii var packardiae, Astragalus cusickii var sterilis, Astragalus cusickii, monophyly <br>