Terrestrial biota in the Antarctic are more globally distinct and highly structured
biogeographically than previously believed, but information on biogeographic patterns
and endemism in freshwater communities is largely lacking. We studied biogeographic
patterns of Antarctic freshwater diatoms based on the analysis of species occurrences in a
dataset of 439 lakes spread across the Antarctic realm. Highly distinct diatom floras, both
in terms of composition and richness, characterize Continental Antarctica, Maritime
Antarctica and the sub-Antarctic islands, with marked biogeographic provincialism in
each region. A total of 44% of all species is estimated to be endemic to the Antarctic, and
most of them are confined to a single biogeographic region. The level of endemism
significantly increases with increasing latitude and geographic isolation. Our results have
implications for conservation planning, and suggest that successful dispersal of
freshwater diatoms to and within the Antarctic is limited, fostering the evolution of
highly endemic diatom floras