Ophiostomatales is an order of fungi in the class Sordariomycetes. It includes both plant and insect pathogens, as well as saprobes (organisms that live on dead or decaying organic matter). The order contains several genera that are important economically, including Ceratocystis and Ophiostoma, which contain species that cause diseases in trees such as Dutch elm disease and oak wilt. Members of this order produce asexual spores called conidia in specialized structures called conidiophores, and sexual spores called ascospores in ascus fruiting bodies. They are often found in sapwood and bark of trees, and can be disseminated by insect vectors or through the movement of wood products.