As natural products, PXA and other phomoxanthones occur as secondary metabolites in fungi of the eponymous genus Phomopsis, most notably in the species Phomopsis longicolla. This fungus is an endophyte of the mangrove plant Sonneratia caseolaris. However, it has also been identified as a pathogen in other plants, such as the soybean plant in which it causes a disease called Phomopsis seed decay (PSD).