Riessa semiophora is an imperfect fungus with basidiomycetous affinities. In culture, the fungus produces two types of conidia: unicellular microconidia and the compound stauroconidia that typify the genus. Both types of conidia are dikaryotic and on germination give rise to a mycelium bearing clamp connections. Their ontogeny is holoblastic, the microconidia arising as separate blown-out points on the apex of the conidiophore, while the stauroconidia develop by the enlargement of the conidiophore apex into, usually, four lobes. Each cell of the stauroconidium is binucleate and capable of germination.