Patterns of Clonal Diversity in Geographically Marginal Populations of Antennaria rosea (Asteraceae: Inuleae) from Subarctic Alaska and Yukon Territory

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Antennaria rosea (Asteraceae: Inuleae) is a herbaceous perennial that reproduces by gametophytic apomixis and is widespread in the cordillera of western North America, ranging from New Mexico to Alaska. In the overall pattern of population structure in A. rosea, the majority of the populations are polyclonal, although the average number of clones per population is relatively small (X̄ = 3.1). In general, clones are restricted to one or two populations (X̄ = 1.1) and, therefore, very few widespread clones exist. The subarctic populations are characterized by relatively low amounts of clonal diversity when compared with those from southern latitudes (X̄ = 2.0/population). Clonal diversity is negatively correlated with latitude, longitude, and elevation of the sites. It seems unlikely that A. rosea survived the last glacial episode in the northern glacial refugium, Beringia, and a more likely scenario for the phytogeographic pattern of clonal diversity is one that envisions A. rosea surviving the Wisconsinan south of the glacial margin or perhaps arising in the same region at the end of the Wisconsinan. New clones probably arise via crossing of facultatively apomictic clones of A. rosea to their sexual progenitors. As most of the eight sexual progenitor taxa are absent from the north, new clones cannot easily arise there. The lack of clonal diversity in the subarctic and arctic could be the result of a combination of recent migration and lack of sexual progenitors in the region.