In: Sydowia 78, (2026): 233-258; ISSN 0082-0598, DOI 10.12905/0380.sydowia78-2026-0233, Published online on january 12th, 2026

Three new orders and five new families in the vesicular-arbuscular mycorrhizal (VAM) fungi of the Glomeromycetes class in the phylum Glomeromycota

Fritz Oehl, Ewald Sieverding, Viviane Monique Santos, Daniele Magna Azevedo de Assis, Thays Gabrielle Lins de Oliveira, Mike Anderson Corazon-Guivin & Gladstone Alves da Silva

Agroscope, Competence Division for Plants and Plant Products, Plant Protection Products – Impact and Assessment, Müller-Thurgau-Strasse 29, CH-8820 Wädenswil, Switzerland
Institute of Agricultural Sciences in the Tropics (Hans-Ruthenberg Institute), University of Hohenheim, Garbenstr. 13, D-70599 Stuttgart-ohenheim, Germany
Departamento de Micologia, CB, Universidade Federal de Pernambuco, Cidade Universitária, Av. da Engenharia s/n,Recife 50740-600, PE, Brazil
Laboratorio de Biología y Genética Molecular, Universidad Nacional de San Martín, Jr. Amorarca N 315, Morales 22201, Peru

* e-mail fritz.Oehl@agroscope.admin.ch

Oehl F., Sieverding E., Santos V.M., Assis D.M.A., Oliveira T.D.L, Corazon-Guivin M.A. & Silva G.A. (2026) Three new orders and five new families in the vesicular-arbuscular mycorrhizal (VAM) fungi of the Glomeromycetes class in the phylum Glomeromycota. – Sydowia 78: 233–258.

The objective was to analyze the phylogeny and morphology of the Glomeromycetes on the order level hitherto consisting of Glomerales, Entrophosporales, Diversisporales and Gigasporales. The updated data sets show that Pacisporaceae is near to Gigasporales, but without support to place this family in Gigasporales or Diversisporales, while the Acaulosporaceae and Sacculosporaceae clades clearly separate from Diversisporaceae. The phylogeny indicates the transfer of Pacisporaceae from the Diversisporales to the new order Pacisporales. Pacisporales differ from all families in Gigasporales by type of spore formation, as forming spores on subtending hyphae instead on suspensors, by formation of vesicular-arbuscular mycorrhiza, and by germination characteristics. The phylogenetic analysis supports the separation of Acaulosporaceae and Sacculosporaceae from Diversisporales, from each other, and from all other Glomeromycetes orders. These two families are transferred to Acaulosporales and Sacculosporales. Acaulosporales are characterized by spore formation in a clear distance from globose termini of sporiferous saccules, three spore walls and generally by the diagnostic, ‘beaded’ inner wall. In Sacculosporales, there is no distance between the bi-walled spores and saccule termini, and the inner wall is never ‘beaded’. Additionally, four new families are separated within Glomerales, and one new family within Diversisporales.

Key words: molecular phylogeny, systematics, classification, arbuscular mycorrhiza, AM fungi, Rhizoglomeraceae.