Two ascomycete classes based on fruiting-body characters and ribosomal DNA sequence.

Traditional fruiting body-based classification of ascomycetes has been under attack for 2 decades. Fruiting-body types can converge, and few researchers now assume that either the closed fruiting bodies (cleistothecia) characterizing the class Plectomycetes or the flask-shaped fruiting bodies (perithecia) characterizing the class Pyrenomycetes are stable, unifying characters. Unless we identify characters uniting major ascomycete groups, orders of ascomycetes remain narrowly defined, and supraordinal classification is impossible. We sequenced both strands of 18s rDNA from nine ascomycete fungi, adding three sequences from GenBank into our analysis. The phylogeny, inferred from 162 informative sites in 1,700 bp of DNA sequence data and using yeast as an outgroup, divided the fungi into two groups correlating well both with fruiting-body type and with the traditional classes Plectomycetes and Pyrenomycetes. Each group received strong statistical support. Genera producing cleistothecia, such as Talaromyces (with a Penicillium asexual state) and the human pathogen Ajellomyces capsulatus (causing histoplasmosis), fall within the plectomycete group. Plectomycetes also includes Eremascus albus and the bee pathogen Ascosphaera apis, although both lack typical fruiting bodies. The Dutch elm disease fungus groups with pyrenomycetes such as Neurospora, in spite of its confusing mixture of class-level characters.