The classification proposed by Gerdemann & Trappe (1974) presented in the classic manuscript “The Endogonaceae in the Pacific Northwest” was entirely based on spore phenotypic characters. The authors proposed this classification based on material collected mainly in the Northwest region of the USA as well as material borrowed from different herbaria.
The authors recognized the genus Glomus as valid and distinct from Endogone (Tulasne & Tulasne had synonymized Glomuswith Endogone) and erected the genus Acaulospora and Gigaspora. In this classification, the AMF were placed in the Order Endogonales, in the Phylum Zygomycota, together with Endogone, Glaziella and Modicella. The last two genera were later transferred to other families and phyla.
Phylum: Zygomycota
Class: Zygomycetes
Order: Endogonales
Family: Endogonaceae
Genera: Glomus, Acaulospora, Gigaspora, Sclerocystis
Gerdemann JW, Trappe JM (1974) The Endogonaceae in the Pacific Northwest. Mycol Mem 5:1–76