The phylogenetic relationships of the anaerobic chytridiomycetous gut fungi (Neocallimasticaceae) and the Chytridiomycota. II. Cladistic analysis of structural data and description of Neocallimasticales ord.nov.

Abstract

We investigated the phylogenetic relationships of the Chytridiomycota and the chytridiomycetous gut fungi with a cladistic analysis of 42 morphological, ultrastructural, and mitotic characters for 38 taxa using both maximum parsimony and distance algorithms. Our analyses show that there are three major clades within the Chytridiomycota: the gut fungi, the Blastocladiales, and the Spizellomycetales–Chytridiales–Monoblepharidales. Consequently, we elevated the gut fungi to the order Neocallimasticales ord.nov. Our results suggest that a modified Chytridiales, including the Monoblepharidales, is a monophyletic group. In contrast the Spizellomycetales are paraphyletic because the Chytridiales arose within them. The separation of the traditional Chytridiales into two orders is thus doubtful. Although the Blastocladiales are closer to members of the Spizellomycetales than the Chytridiales, the cladistic analyses of both structural and rRNA sequence data do not support the idea that the Blastocladiales were derived from the Spizellomycetales. We suggest emendations to the classification of the Chytridiomycota and note which groupings require further analysis. Our phylogeny for the currently recognized species of gut fungi is inconsistent with the existing classification. Nonetheless, pending further investigations, we prefer to retain the existing, easily defined genera for which a key is provided. Key words: Chytridiomycota, rumen fungi, phylogeny, morphology, ultrastructure, mitosis.