Ambispora leptoticha

(reference accession FL130A)

Before Ambispora leptoticha was recognized as being dimorphic, each spore type had been classified as members of separate families (Acaulosporaceae and Glomeraceae). Some of these species needed synonymization Morton et al. (1997) so that four species (two in Glomus and two in Acaulospora) were reduced to two species (one in Glomus and one in Acaulospora). These changes are summarized immediately below.

Acaulosporiod synanamorph

Glomoid synanamorph

Morpotypes

The next step (same paper) was to recognize that both of these “species” were different morpotypes of the same organism and to use the first assigned name (nomenclatural priority). That name was Acaulospora leptoticha. Morphology alone couldn’t go any further because homologies were uncertain with so much divergence between two families. Sequence data, which is universal to all living organism, bridges this developmental gap. SSU data verified the dimorphism and also determined that this species was in a completely different than either Glomus or Acaulospora and was more deeply rooted (Redecker et al., 2000). Other related species became recognized and placed in a new genus and family, Archaeospora, Archaeosporaceae (Morton et al. 2001).

Spain et al. (2006) took steps to place the dimorphic species into a new genus (Appendicispora) and to keep the strictly acaulosporoid species (Ar. trappei) separate. But then these workers created a huge mess by resurrecting all of the species that had been synonymized into Ar. leptoticha. They did this by focusing only on a few select morphological characters that appeared discrete but in reality were extremes in a continuum of variation. So the entire exercise was based on artifacts, but it has been perpetuated in the literature (a taxonomic conundrum). Walker et al. (2007a) independently recognized another dimorphic species and Glomus callosum as being most closely related to Ar. leptoticha and Ar. gerdemannii sensu lato and placed them all in a new genus Ambispora.

Nomenclatural priority necessitated that this genus name be dumped and all of the taxa transferred to Appendicispora (Walker et al., 2007b). But then these workers later discovered the name Appendicispora was in use by a different group of organisms (a homonym) and Ambispora was resurrected (the second coming?). But now all those pesky Glomus and Acaulospora species separated out by Spain et al. (2006) were retained and they became member species in Ambispora (Walker, 2008). So now we have a genus with species forming glomoid spores only, acaulosporoid spores only, or forming dimorphic spores. Make sense yet? Smile, don’t cry—it doesn’t solve anything. Regardless of your take on all this, Am. leptoticha (and Am. gerdemannii) are true species. We have worked that out using clearly congruent morphological and molecular data from 15 accessions together with sequences from GenBank. This information is being reported in a manuscript in Mycorrhiza, which has been accepted for publication and will appear shortly online (Feb-Mar, 2015).

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