Acaulospora colossica sp nov from an old field in North Carolina and morphological comparisons with similar species, A-laevis and A-koskei

A new arbuscular mycorrhizal fungal species, Acaulospora colossica, (Glomal es, Acaulosporaceae) is described, and its distribution and seasonality dis cussed. Spores of A. colossica develop from saccules that empty their conte nts in the developing spores. Spore wall structure consists of 3 layers, al l originating from the subtending hyphae. The two inner layers are laminate d. The outermost spore wall layer is typically sloughed off before the spor es mature. Two inner walls arise sequentially. Both inner walls are compris ed of two layers. The outer layer of the innermost wall is beaded. Acaulosp ora colossica is described from a population in Durham, North Carolina. Its name refers to the relatively large size of the spores. Finally, the morph ology of the new species A. colossica is compared and contrasted to two clo sely related species A. laevis and A. koskei.