Evolutionary Relationships Among Arbuscular Mycorrhizal Fungi in the Endogonaceae

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Abstract
A cladistic analysis of 57 species in six genera of the Endogonaceae was performed using 27 morphological characters of asexual spores and the endophytic phase of mycorrhizal development. These species comprised a monophyletic group defined by two synapomorphies: mutualistic symbiosis with terrestrial plants and production of specialized dichotomously branched intraradical arbuscules interfacing host and fungal symbiont. Members of Endogone, another genus in the Endogonaceae, did not share these characters and thus were a polyphyletic group related to some arbuscular species in Glomus and Sclerocystis only by convergence. Two main branches were hypothesized to have evolved from a common arbuscular ancestor. One branch consisted of Gigaspora and Scutellospora, as defined by extraradical auxiliary cells and spores formed within a thin unit wall on a sporogenous cell. The other branch consisted of Glomus, Sclerocystis, Acaulospora, and Entrophospora, as defined by intraradical vesicles in mycorrhizal roots. Parallelisms were numerous within all descendant monophyletic fungal groups, lowering resolution of branching patterns. The cladogram and phylogenetic tree reconstructed from this analysis establish a theoretical framework for future studies.