The AM fungal family Archaeosporaceae and the genus Archaeospora are rendered paraphyletic by the relationship with the Geosiphonaceae. This problem led to a more detailed study of the Archaeosporales. Members of the Archaeosporaceae were described as forming both glomoid and acaulosporoid spores, or solely acaulosporoid spores. However, we found that Glomus callosum fell into the same phylogenetic clade as A. leptoticha and A. gerdemannii, but exclusively formed glomoid spores. To resolve these inconsistencies, a genus, Ambispora gen. nov., typified by Ambispora fennica sp. nov., is erected based on morphological evidence and SSU and ITS region rDNA data. Ambispora contains three species known to produce both acaulosporoid and glomoid spores: A. fennica, A. leptoticha comb. nov. (basionym G. leptotichum), and A. gerdemannii comb. nov. (basionym G. gerdemannii). Another species, A. callosa comb. nov. (basionym G. callosum), is known only from glomoid spores. Ambispora is placed in a new family, the Ambisporaceae fam. nov. The Archaeosporaceae is maintained with the type species, Archaeospora trappei (basionym Acaulospora trappei), along with Intraspora schenckii (basionym Entrophospora schenckii). Acaulospora nicolsonii, known only from acaulosporoid spores, is discussed and is considered likely to belong in the Ambisporaceae, but is retained within its present genus because of inadequate morphological information and a lack of molecular data.