The proportion of
polyploid plant species increases at higher latitudes, and it has been suggested that original postglacial Arctic immigrants of some large groups, including grasses, were
polyploid. We analyzed noncoding nuclear and
chloroplast DNA of all North American diploid Puccinellia (Poaceae) and a subset of arctic
polyploids to hypothesize evolutionary relationships among diploids and to evaluate the parentage of
polyploids. Diploids formed three lineages: one uniting arctic species P. arctica and P. banksiensis; a second comprising arctic species P. tenella, P. alaskana, P. vahliana, and P. wrightii; and a third uniting the two temperate species P. lemmonii and P. parishii. The arctic species P. angustata (hexaploid) and P. andersonii (primarily octoploid) apparently derive from the P. arctica-P. banksiensis lineage based on ITS and chloroplast sequences, and share an ancestor with arctic
triploid/
tetraploid P. phryganodes based on nrDNA sequences. Sequence comparisons also suggest
tetraploid P. bruggemannii evolved from two arctic lineages: P. vahliana-P. wrightii and P. arctica-P. banksiensis. These patterns and the predominance of arctic rather than temperate diploid species support the idea that diploid Puccinellia recolonized the Arctic from northern glacial refugia like Beringia, and also formed stabilized
polyploid hybrids during these refugial events or subsequently during postglacial colonization.