Polyploidy, infraspecific cytotype variation, and speciation in Goldenrods: The cytogeography of Solidago subsect. Humiles (Asteraceae) in North America

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Abstract:

Polyploidy is an important evolutionary mechanism in plants, and in some genera (e.g., Solidago in Asteraceae) it is particularly widespread and is hypothesized to have played a major role in diversification. Goldenrods are notorious for their ploidy variation, with roughly 14% and 32% of recognized North American species being polyploid or including multiple cytotypes, respectively. We used traditional chromosome counts and flow cytometry to examine cytogeographic patterns, biogeographic and evolutionary hypotheses, and species boundaries in S. subsect. Humiles. Chromosome numbers and DNA ploidy determinations are reported for 337 individuals, including 148 new reports. Cytotypes show significant geographic structuring. Solidago simplex and S. spathulata were uniformly diploid (2n = 18) in western North America, while cytogeographic patterns in eastern North America were regionally complex and included 2n, 4n, and 6n cytotypes. Cytotypes within S. simplex were ecogeographically segregated and mixed-ploidy populations were rare. Data from this study and additional biosystematic data indicate that cytotypes in S. simplex fulfill the requirements of multiple species concepts and should best be treated as distinct species. Polyploid cytotypes possibly formed recurrently, however, and evolution and species boundaries within poly ploid S. simplex will require additional study. Results from this study and accumulated data from other studies suggest that biological species diversity in Solidago is considerably higher than currently recognized taxonomically.

Keywords: CYTOGEOGRAPHY; FLOW CYTOMETRY; GENOME SIZE; NORTH AMERICA; POLYPLOIDY; SOLIDAGO

Document Type: Research Article

Affiliations: 1: Department of Ecology and Evolutionary Biology, The University of Michigan, Ann Arbor, Michigan 48109-1048, U.S.A., The University of Michigan Herbarium, 3600 Varsity Drive, Ann Arbor, Michigan 48108-2228, U.S.A.;, Email: peirsonj@umich.edu 2: The University of Michigan Herbarium, 3600 Varsity Drive, Ann Arbor, Michigan 48108-2228, U.S.A. 3: Department of Biology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada

Publication date: February 21, 2012

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