SUMMARYMikronegeria albaonNothofagus(Fagaceae) species in Chile and Argentina has as its gametophytic stateCaeoma espinosaeonAustrocedrus(Cupressaceae). Lack of spore pigment, morphological details, and distinctly different aecial stages separateM. albafrom the sympatricM. fagi, also onNothofagus. Mikronegeriais difficult to classify; it may display more“primitive”characteristics than other heteroecious genera of Uredinales.