Chapter 13: Phylum Ascomycota: Filamentous Ascomycetes with Apothecia—Discomycetes

The perithecial structure itself represents a key organizing principle, featuring an internal layer of asci embedded within a sterile tissue matrix, along with supporting filaments known as paraphyses and periphyses that facilitate spore release and dispersal. The chapter provides detailed examination of three representative genera that illustrate the range and significance of this group: Neurospora crassa, which revolutionized genetics and molecular biology through its ability to produce ordered ascospores in linear asci, enabling researchers to map genes and decode fundamental aspects of biochemical pathways and the genetic code; Claviceps purpurea, a cereal pathogen whose sclerotia produce ergot alkaloids capable of causing ergotism, a disease with historical significance and contemporary pharmaceutical applications; and Nectria species, plant pathogens responsible for causing destructive cankers and blights on woody plants. Beyond sexual reproduction via ascospores, many pyrenomycetes employ asexual reproductive strategies through the production of conidia, which extend their dispersal capacity and ecological impact. The chapter contextualizes these fungi within broader ecological and applied frameworks, addressing their roles as decomposers of plant material, aggressive plant pathogens affecting agricultural productivity, endophytic colonists of living plant tissues, and experimental organisms that have shaped modern biological science. Attention to ascus dehiscence mechanisms, spore morphology, and developmental patterns provides students with a comprehensive understanding of perithecial reproduction and the structural innovations that characterize this functionally important fungal group.