Two new species of Pleosporales from northern Thailand: Anastomitrabeculia chiangraiensis sp. nov. (Anastomitrabeculiaceae) and Roussoella chiangraiensis sp. nov. (Roussoellaceae).

Pleosporales is a highly diverse order in Dothideomycetes, with numerous taxa occupying saprobic, pathogenic and endophytic niches worldwide. During a survey of microfungi in northern Thailand, two sexual morph species were collected and examined, based on morphology and multigene phylogenetic analyses (28S, ITS, 18S, tef1-α and rpb2). Based on this approach, two new species were introduced. Anastomitrabeculia chiangraiensis sp. nov., isolated from a dead stem of an unidentified woody host, forms a distinct lineage within Anastomitrabeculiaceae and can be distinguished from its sister taxon, A. didymospora, by the absence of longitudinal striations in the ascospores and high interspecies sequence divergence in the ITS, 28S and rpb2 regions. Roussoella chiangraiensis sp. nov., collected from dead bamboo stems, is well-resolved within Roussoellaceae and differs from the closely-related R. aseptata with robust phylogenetic support (100% ML, 1.00 PP) and significant interspecies genetic distance in ITS. Morphological differentiation from R. aseptata was restricted due to the absence of a known sexual morph for that species. Our findings highlight the high, yet underexplored diversity of saprobic Pleosporales in Southeast Asia and underscores the importance of integrative morphological and phylogenetic approaches for accurate species recognition.