A new polymorphic species of Laboulbenia parasitic on a South American fly.

Morphologically different thalli of Laboulbenia richardiana sp. nov. (Laboulbeniales, Ascomycota) were found on various parts of the body of the South American fly Richardia teevani. These thalli lack a separate cell IV and have similar appendages and perithecial apices. They are interpreted here as 'growth forms' of a single biological species. Spore characteristics and insect behavior support this view, rather than the hypothesis of several different species displaying position specificity.