Three new species of acanthostigma (Tubeufiaceae, Dothideomycetes) from Great Smoky Mountains National Park.

Three new bitunicate ascomycetes belonging to the genus Acanthostigma are described from terrestrial decomposing wood collected from Great Smoky Mountains National Park, USA. Phylogenetic analyses of the nuclear ribosomal 28S large subunit and internal transcribed spacer region placed all three species in the Tubeufiaceae and confirmed morphological analyses that these are distinct species. Expanded phylogenetic analyses of 28S large subunit including taxa throughout the Dothideomycetes confirmed the placement of Acanthostigma in the Tubeufiaceae. Acanthostigma filiforme differs from other Acanthostigma species in having longer ascospores with more septa. Acanthostigma multiseptatum can be distinguished in having longer asci and longer ascospores with more septa. Acanthostigma septoconstrictum differs in having longer setae and asci and broader, asymmetrical ascospores that are constricted at their septa. A dichotomous key to Acanthostigma species is provided.