Data from: Global biogeographic patterns in bipolar moss species

A bipolar disjunction is an extreme, yet common, biogeographic pattern in
non-vascular plants, yet its underlying mechanisms (vicariance or
long-distance dispersal), origin and timing remain poorly understood.
Here, combining a large-scale population dataset and multiple dating
analyses, we examine the biogeography of four bipolar Polytrichales
mosses, common to the Holarctic (temperate and polar Northern Hemisphere
regions) and the Antarctic region (Antarctic, sub-Antarctic, southern
South America) and other Southern Hemisphere (SH) regions. Our data reveal
contrasting patterns, for three species were of Holarctic origin, with
subsequent dispersal to the SH, while one, currently a particularly common
species in the Holarctic (Polytrichum juniperinum), diversified in the
Antarctic region and from here colonized both the Holarctic and other SH
regions. Our findings suggest long-distance dispersal as the driver of
bipolar disjunctions. We find such inter-hemispheric dispersals are rare,
occurring on multi-million-year timescales. High-altitude tropical
populations did not act as trans-equatorial ‘stepping-stones’, but rather
were derived from later dispersal events. All arrivals to the Antarctic
region occurred well before the Last Glacial Maximum and previous
glaciations, suggesting that, despite the harsh climate during these past
glacial maxima, plants have had a much longer presence in this southern
region than previously thought.