PHYLOGENETIC-RELATIONSHIPS AMONG THE HARPELLALES AND KICKXELLALES

DNA sequences of the nuclear encoded small subunit (SSU) 18S ribosomal RNA gene and characters from a morphological/physiological dataset we re analyzed by maximum parsimony to investigate phylogenetic relations hips among and within two putative sister orders of Zygomycota that pr oduce regularly septate hyphae with ultrastructurally similar plugged, flared septal pores, the Harpellales and Kickxellales. The most parsi monious trees (MPT) inferred from the molecular data, using Chytridium -Spizellomyces and Rhopalomyces as outgroups in separate analyses, wer e largely concordant. Cladistic analysis of nucleotide characters iden tified three strongly supported monophyletic lineages that formed an u nresolved trichotomy in the 18S rDNA gene trees: the Harpellales, Kick xellales and a Spiromyces clade. Trees inferred from the nonmolecular data were largely unresolved and generally poorly supported by bootstr ap and decay analyses. However, results of a partition-homogeneity tes t detected no positive conflict between the morphological and molecula r datasets, indicating that they could be combined, Morphological evol ution was investigated by optimizing nonmolecular characters on the 18 S rDNA gene tree. Systematic results support the recognition of a Spir omyces clade independent of the Kickxellales where it is currently cla ssified and the apparent paraphyly of Coemansia with Spirodactylon der ived within it. A formal diagnosis of Spiromyces aspiralis sp. nov is provided together with an emendation of the genus.