During our investigation of palm fungi in Thailand, two interesting taxa from Elaeis guineensis and Metroxylon sagu (Arecaceae) were collected. Based on phylogenetic analyses of a combined dataset of ITS, LSU, rpb2, and tub2 nucleotide sequences as well as unique morphological characteristics, we introduce the new genus Haploanthostomella within Xylariales, and a new species Endocalyx metroxyli. Additionally, in our study, the genus Endocalyx is transferred to the family Cainiaceae based on its brown conidia and molecular phylogenetic evidence.