Long-term plant survival at high latitudes

Summary Long-term survival is a feature of plant life in the Arctic both for individuals and species. Stems of willow can be centuries old and vegetatively reproducing clones can have their ages counted in millennia. Circum-polar examination of chloroplast DNA has made it possible to trace the migration of Saxifraga oppositifolia clades over a period of 4–5 million years and demonstrate that this species maintained a presence north of the ice sheets during the last glacial maximum and probably longer. There has long been speculation that the Arctic has two distinct floras, an ancient autochthonous flora (an original endemic flora) that has survived since the Pleistocene and an invading flora that has immigrated into the Arctic during late glacial and post-glacial times. It is therefore probable that Saxifraga oppositifolia is not alone in its Pleistocene occupation of High Arctic polar deserts. The ancient autochthonous flora consists of conservative species with widespread distributions and chromosome counts that are simple diploids, with little evidence of allo-polyploidisation. This is in marked contrast to the majority of the species that are now present in the Arctic which are polyploid. This paper considers some of the physiological and genetic properties of polar-plant-populations that may facilitate persistence in uncertain and heterogeneous adverse environments. Attention is drawn to some possible advantages that diploid species may possess over polyploids, in having a mutualistic rather than a competitive relationship between varying sub-populations and local ecotypes whereby, diploid species, consisting of many variable populations that readily interbreed, provide a mutually accessible source of genetic variation that may have contributed to long-term survival.