Population genetic structure of the ectomycorrhizal fungus Laccaria sp. A resembles that of its host tree Nothofagus cunninghamii

• Highest allelic diversity in Tasmanian populations of Laccaria sp. A.
• Tasmanian population panmictic with unrestricted gene flow.
• Victorian populations exhibit genetic structure across geographic regions.
• Evidence of glacial refugia across range as well as post-glacial migration in Victoria.
• Laccaria sp. A genetic structure congruent with that of host, Nothofagus cunninghamii.

The ectomycorrhizal fungus Laccaria sp. A is restricted to temperate rainforest of southeast Australia, associated with its host tree Nothofagus cunninghamii. Eight mitochondrial microsatellite markers were used to investigate the population genetic structure of L. sp. A across its distribution in Tasmania and Victoria. The highest allelic diversity was found in Tasmania, which appeared to contain a panmictic population, whereas the more fragmented Victorian populations were characterized by low allelic diversity and differentiation between east and west. There is evidence of glacial refugia in the west and the northeast of Tasmania, and in Victoria in the Otway Ranges and Central Highlands, with postglacial migration into the Strzelecki Ranges. Narrow host-specificity may have contributed to the presence of population structure in this fungus. Allelic diversity patterns in L. sp. A are largely congruent with diversity patterns already established in populations of its host, N. cunninghamii.