Achroceratosphaeria, a new ascomycete genus in the Sordariomycetes, and re-evaluation of Ceratosphaeria incolorata

A new ascomycete genus, Achroceratosphaeria, is described for three lignicolous species from freshwater and terrestrial habitats in Asia and Europe on the basis of morphological studies and phylogenetic analysis of combined nc28S (LSU) and nc18S (SSU) rDNA sequence data. The new genus is characterized by minute, hyaline or subhyaline to pale brown perithecia immersed in the substratum with hyaline to subhyaline emergent necks. Paraphyses disintegrate with age, asci are cylindrical-clavate with a distinct apical annulus containing eight hyaline ascospores; ascospores are smooth-walled, ranging from ellipsoidal to fusiform to cylindrical-fusiform, without a mucilaginous sheath or appendages. All three species were obtained after incubation in a moist chamber. Achroceratosphaeria resembles Ceratosphaeria, Pseudohalonectria or Clohiesia in ascospore morphology, but molecular data do not support these relationships. In our phylogeny, a relationship between Achroceratosphaeria and taxa in the Lulworthiales and Koralionastetales is confirmed. Ceratosphaeria incolorata is transferred to Achroceratosphaeria and a new combination is proposed. A key to the species accepted in Achroceratosphaeria is provided.