An Eight-Gene Molecular Phylogeny of the Kickxellomycotina, Including the First Phylogenetic Placement of Asellariales

Kickxellomycotina is a recently described subphylum encompassing four zygomycete orders (Asellariales, Dimargaritales, Harpellales, Kickxel- lales). These fungi are united by the formation of disciform septal pores containing lenticular plugs. Morphological diversification and life history evolu- tion has made the relationships within and among the four orders difficult to resolve on those grounds alone. Here we infer the phylogeny of the Kickxello- mycotina based on an eight-gene supermatrix includ- ing both ribosomal rDNA (18S, 28S, 5.8S) and protein sequences (MCM7, TSR1, RPB1, RPB2, b- tubulin). The results of this study demonstrate that Kickxellomycotina is monophyletic and related to members of the Zoopagomycotina. Eight unique clades are distinguished in the Kickxellomycotina, including the four defined orders (Asellariales, Dimargaritales, Harpellales, Kickxellales) as well as four genera previously placed within two of these orders (Barbatospora, Orphella, Ramicandelaber, Spir- omyces). Dimargaritales and Ramicandelaber are the earliest diverging members of the subphylum, al- though the relationship between these taxa remains uncertain. The remaining six clades form a mono- phyletic group, with Barbatospora diverging first. The next split divides the remaining members of the subphylum into two subclades: (i) Asellariales and Harpellales and (ii) Kickxellales, Orphella and Spir- omyces. Estimation of ancestral states for four poten- tially informative morphological and ecological char- acters reveals that arthropod endosymbiosis might have been an important factor in the early evolution of the Kickxellomycotina.