Welcome to migrants in a borderless Europe: bryophytes show the way to go

Reconstructing the Quaternary history of European bryophytes has long been challenging
because, except for macro-remains preserved in peat, the fossil record is extremely poor as
compared to vascular plants. Coalescent simulations revealed that the postglacial assembly
of European bryophytes involves a complex history from multiple sources, contrasting
with the prevailing model of northwards species migration from Mediterranean refugia.
A scenario of extra-European postglacial recolonization clearly emerged as dominant. A
bulk of the bryoflora that pre-existed in Europe before the Ice Age was reinforced by allochthonous migrants. The Atlantic European fringe was, in contrast, de novo colonized by
species primarily distributed across tropical areas. We hypothesize that, for the particular
case of the oceanic bryophyte floristic element, the Macaronesian islands represented a
mandatory stepping-stone situated midway between the tropics and Europe due to the
necessity for tropical species to pre-adapt under insular warm-temperate conditions before
they successfully establish in temperate regions.