In vitro morphogenesis and ultrastructure of a Frankia sp. ArI3 (Actinomycetales) from Alnus rubra and a morphologically similar isolate (AirI2) from Alnus incana subsp. rugosa

An actinomycete (AirI2) with black spores was isolated from nodules of Alnus incana ssp. rugosa. Although this organism is very different in appearance from the typically white strains of Frankia from Alnus, it has all the main microscopic features of members of this genus. However, cytological differences have been observed when compared with a strain with white spores (ArI3).