Abstract
Zygosporium species are widespread on hosts and usually associated with monocotyledonous plants including Arecaceae (palms) and Pandanaceae. Zygosporium forms colonies as darkened spots on the host surface. This study recovers two Zygosporium species from China and Thailand and makes an attempt to clarify the systematic placement of Zygosporium based on morphological characteristics and phylogenetic analyses based on rDNA sequence data. Phylogenetic analyses of a combined LSU and ITS sequence data generated under Maximum Likelihood and Bayesian criteria indicate that Zygosporium species form a strongly supported monophyletic lineage basal to the Coniocessiaceae and not to the Microdochiaceae as previously assumed. Given the distinct morphological features of Zygosporium and its strongly supported monophyletic nature, a new family, Zygosporiaceae is introduced within the Xylariales.