Abstract
Two new Helicascus species H. chiangraiensis and H. uniseptatus from submerged wood in aquatic habitats in northern Thailand are introduced in this paper based on morphology and molecular analysis of DNA sequence data. Descriptions and illustrations of H. chiangraiensis and H. uniseptatus are provided. Helicascus chiangraiensis is characterized by its unilocular ascostromata, verrucose-walled ascospores with 2-4 large refractive guttules. Helicascus uniseptatus is characterized by its unilocular, small ascostromata, and uniseptate, smooth-walled ascospores lacking a mucilaginous sheath. Phylogenetic analysis based on combined ITS, LSU and TEF1a sequence data placed these species in Morosphaeriaceae (Pleosporales).