Morpho-molecular analyses reveal a novel species Acrocalymma hibisci and a new host record of Acrocalymma medicaginis

Dead stems of Hibiscus rosa-sinensis and Tithonia diversifolia were collected from Chiang Rai Province, in northern Thailand and examined for microfungi. Two species of Acrocalymma were observed. Multigene phylogenetic analyses of LSU, SSU and ITS sequences support their placement within Acrocalymmaceae. Acrocalymmaceae (Pleosporales), which includes the single genus, Acrocalymma. This genus is globally distributed and associated with diverse hosts. Acrocalymma is characterized by ostiolate ascomata, furcate, pedicellate asci, and hyaline to brown or pale reddish-brown, obovoid to ellipsoid ascospores. The asexual morph has smooth-walled conidiogenous cells and cylindric-clavate to fusiform, guttulate conidia with a helmet-shaped mucilaginous appendage at the apex. Based on morphology and molecular data, we report the new species Acrocalymma hibisci on H. rosa-sinensis and a new host record of A. medicaginis on T. diversifolia. Acrocalymma hibisci differs from other species by having seven-septate conidia. This study presents comprehensive descriptions and micrographs of the isolates along with multigene phylogenetic data.