The order Arthoniales is a group of mostly lichen-forming fungi within the class Arthoniomycetes. Members of this order are primarily crustose lichens, often growing on bark, rocks, or leaves, and are characterized by their symbiotic association with photosynthetic partners, usually green algae. Arthoniales exhibit a diverse range of reproductive structures, including both sexual and asexual spores, and many species have specialized chemical compounds used in lichen identification. They are ecologically significant, contributing to nutrient cycling, habitat formation, and serving as bioindicators of environmental health, particularly air quality. Despite their often inconspicuous appearance, Arthoniales are a highly diverse and widely distributed group of fungi.