Parallel evolutionary patterns in multiple lineages of arctic Artemisia L. (Asteraceae).

Early observers of plant evolution in the Arctic have noted a floristic similarity with temperate alpine regions and a predominance of high ploidy levels. The aim of our study was to survey these and other traits in multiple closely related but independently evolved lineages of Artemisia. Our phylogenetic study was based on 133 taxa using 3'-ETS and ITS, and on data on morphology, karyology, distribution, and ecological preferences. We compared Arctic lineages with sister groups and tested whether patterns were significantly different. We found: (1) Artemisia has independently adapted to Arctic habitats 13-18 times; (2) There were no ecological preferences of putative progenitors that might determine the colonization success in the Arctic, although most sister groups were centered in steppe habitats; (3) Plant height was distinctly reduced in Arctic lineages; (4) Arctic lineages contained no more polyploids than their respective sister groups or taxa from other habitats; (5) Enlarged flower heads have evolved repeatedly, probably for better pollinator attraction. This strategy could be a substitute for polyploidy, which is typical in other Arctic taxa. Stronger pollinator attraction should result in better outcrossing and higher heterozygosity in the offspring, which is among the main effects of polyploidy.