Phylogenetic Review of Acaulospora (Diversisporales, Glomeromycota) and the Homoplasic Nature of Its Ornamentations

The genus Acaulospora has undergone many updates since it was first described; however, there are some missing pieces in the phylogenetic relationships among Acaulospora species. The present review aimed to: (i) understand the evolutionary meaning of their different spore wall ornamentations; (ii) define the best molecular marker for phylogenetic inferences, (iii) address some specific issues concerning the polyphyletic nature of Acaulospora lacunosa and Acaulospora scrobiculata, and the inclusion of Kuklospora species; and (iv) update the global geographical distribution of Acaulospora species. As such, the wall ornamentation of previously described Acaulospora species was reviewed and phylogenetic analyses were carried out based on ITS and SSU-ITS-LSU (nrDNA). Moreover, the already available type material of A. sporocarpia was inspected. According to the data obtained, temperate and tropical zones are the richest in Acaulospora species. We also confirmed that A. sporocarpia does not belong to Acaulospora. Furthermore, our phylogeny supported the monophyly of Acaulospora genus, including the Kuklospora species, K. colombiana and K. kentinensis. The nrDNA phylogeny presented the best resolution and revealed the homoplasic nature of many ornamentations in Acaulospora species, pointing out their unfeasible phylogenetic signal. This review reinforces the urgency of more molecular markers, in addition to the nrDNA sequences, for the definition of a multi-locus phylogeny.