Acremonium with catenate elongate conidia: phylogeny of Acremonium fusidioides and related species

Acremonium is one of the largest and most complex genera of hyphomycetes. Its taxonomy is not yet resolved and the phylogenetic value of the most distinctive morphological features is unknown. The species of this genus produce conidia in chains or form slimy heads or both. We have studied a set of clinical and environmental Acremonium strains morphologically characterized by producing mostly catenate, elongate, more or less fusiform conidia. Based on phenotypic data and in the analysis of the sequences of the ITS region, the D1/D2 domains of the 28S rRNA gene and a fragment of the β-tubulin gene, three new species morphologically similar to Acremonium fusidioides and belonging to the family Bionectriaceae (Hypocreales) are described and illustrated; they are Acremonium pilosum, Acremonium parvum and Acremonium citrinum. The first species produces two kinds of conidia: clavate with smooth walls and globose with abundant filiform projections. Acremonium parvum is characterized by slow growth and pyriform or slightly lanceolate conidia with an elongate and truncate base. Acremonium citrinum produces a diffusible yellow pigment and obovoid conidia.