Evolutionary assembly of the Arctic flora

Abstract Aim The Arctic is the coldest inhabited region on Earth, and it supports few terrestrial species. The tropical‐climate origin of many angiosperm clades, along with strong phylogenetic niche conservatism, likely constrained colonization of cold environments for many plants. However, invasion of the Arctic by many lineages might also have opened up a new adaptive landscape that facilitated subsequent diversification. We might, therefore, expect species in this biome to be descendants of a few cold‐tolerant lineages. Here, we explore the assembly of the Arctic flora using data on the relationships and distributions of > 80,000 species. Location The Northern Hemisphere. Time period Current. Taxon Flowering plants. Methods The Arctic was divided into five bioclimate subzones. We assembled a species pool for flowering plants in the Northern Hemisphere, and determined which species of the species pool are distributed in the Arctic and each of its subzones. We used two metrics (the standardized effect sizes of mean pairwise distance and Faith’s phylogenetic diversity; MPD ses and PD ses , respectively) to quantify phylogenetic dispersion of flowering plant assemblages. Results When the Arctic species were compared to all the species in the Northern Hemisphere, MPD ses and PD ses were −12.85 and −27.17, respectively, indicating that the Arctic flora is a phylogenetically clustered subset of the Northern Hemisphere species pool. In general, MPD ses and PD ses decreased from the south to the north within the Arctic, indicating that some lineages are further filtered stepwise into more northerly Arctic subzones. Main conclusions The species of the Arctic flora comprise a phylogenetically clustered subset of the broader Northern Hemisphere flora. The more negative value for PD ses compared to MPD ses indicates that clustering is stronger towards the tips of the phylogenetic tree. We suggest that the majority of Arctic species are nested within clades having attributes that enabled adaptation to cold climates.