Chapter 17: Phylum Basidiomycota: Order Agaricales—The Mushrooms

The fundamental feature unifying this assemblage is the presence of locules, which are specialized cavity-like compartments embedded within stromatic tissue that contain the asci and function in spore production and dispersal. The chapter explores the taxonomic complications arising from Ascoloculares species that display overlapping characteristics with other ascomycete groups, particularly Loculoascomycetes and Pyrenomycetes, making definitive classification difficult based on traditional morphological criteria alone. Specific genera such as Myriangium and Elsinoë are examined as representative examples, with emphasis on Elsinoë as the causative agent of citrus scab, an economically significant disease affecting citrus production worldwide. The structural attributes of these fungi are detailed, including the development and organization of locules, the morphology of asci which may be either bitunicate or unitunicate, and the mechanisms of ascospore dispersal and release. Many Ascoloculares species also employ asexual reproduction through the production of conidia, which provides alternative dispersal strategies and enhances survival capacity in different ecological contexts. From an ecological perspective, members of this group occupy diverse niches as saprobes decomposing plant material, as plant pathogens causing agricultural damage and economic losses, and as endophytes living within plant tissues. The agricultural significance of pathogenic Ascoloculares is highlighted through their capacity to reduce crop yields and damage economically important plant species. The chapter reflects critically on how advances in molecular phylogenetic analysis have substantially revised understanding of Ascoloculares classification, leading to the reclassification and reassignment of numerous species to alternative ascomycete lineages. This ongoing taxonomic reorganization underscores a central theme in modern mycology: morphological features alone provide insufficient resolution for accurate evolutionary classification, and integration of molecular genetic data with traditional methods is essential for constructing robust fungal classification systems.