Significance Ascomycetes are a prolific source of natural products that are of great significance for human health, yet production of ribosomally synthesized and posttranslationally modified peptides (RiPPs), a ubiquitous class of natural products, have rarely been reported in this fungal phylum. Here we show that phomopsins, a family of antimitotic mycotoxins, have a ribosomal origin and demonstrate the widespread presence of a fungal RiPP pathway for cyclic peptides that we term dikaritins. The framework described herein provides a foundation for mining for additional dikaritin members and investigating the biological activities and biosynthetic chemistry of this family of fungal natural products.