Phaeosphaeriaceae is a species-rich family in the order Pleosporales, encompassing species with diverse lifestyles viz., endophytic, epiphytic, lichenicolous, phytopathogenic, saprobic and even human pathogenic. In a survey on biodiversity of fungal species associated with leaf spot diseases of herbaceous plants in Iran, a coelomycetous fungus was recovered from symptomatic leaves of Fallopia convolvulus. Morphologically, the fungal isolates resembled species in the genus Parastagonospora. Although the phylogenetic analysis based on combined LSU and ITS sequence data placed these isolates within the family Phaeosphaeriaceae, they clustered distinct from presently known genera in the family. The monotypic genus Parastagonosporella (Phaeosphaeriaceae) is therefore introduced, with Parastagonosporella fallopiae as type species. A detailed description is provided, with notes discussing allied genera in the family.