Archaeospora gerdemannii

This species is one of two in Archaeosporaceae which is distinctly dimorphic, with each spore type classified as a member of separate families (one in Acaulosporaceae and one in Glomaceae). The taxonomic problem of classifying two morphotypes of the same species in separate families has taken some time to resolve. Small subunit (18S) ribosomal DNA sequences finally provided the character set to position this species as ancestral to both Acaulosporaceae and Glomaceae (Redecker et al., 2000). The molecular phylogenetic tree suggests that A. gerdemannii is more closely related to a nonmycorrhizal fungus, Geosiphon pyriforme, which has been classified as a Zygomycete fungus for lack of evidence as to where else to place the species.

Acaulosporoid synanamorph (prior taxonomic history)

None. This spore morphotype was first classified as Glomus gerdemannii by Rose and Trappe (1979). These authors mention the spores bore some resemblance to those of Acaulospora species, but they were unable to find saccules or other structures affirming placement in that genus. The long "pedicel" from spore to saccule neck was mistaken for a Glomus-like subtending hypha -- a very easy mistake to make at that time with no foreknowledge of such a peculiar morphology. It wasn't until this species was propagated in pot culture that it was proven to be an acaulosporoid spore type and needed reclassification. Nothing was done taxonomically for five years after this discovery, for the simple reason that we could not determine from morphological data alone where to place this species.

Glomoid synanamorph (prior taxonomic history)

None. This spore morphotype was discovered only in pot cultures of the species and formal taxonomic study was postponed until nonmorphological data could be collected to complement morphology in resolving phylogenetic relationships.

Archaeospora gerdemannii (reference accession AU215)