Acremonium is generally considered to be a highly polyphyletic form genus containing distantly related fungi. Sectional divisions within Acremonium distinguish the clavicipitaceous grass endophytes of sect. Albolanosa from the generally saprobic species of sections Acremonium, Chaetomioides, Gliomastix, and Nectrioidea. In an effort to assess the possible number of lineages currently placed within Acremon- ium and to determine which groups of sexual asco- mycetes are phylogenetically affiliated with Acremon- ium species, maximum parsimony and neighborjoin- ing analyses were performed using partial sequences of the nuclear small subunit ribosomal DNA (18S rDNA). Acremonium was shown to be a polyphyletic taon with affiliations to at least three ascomycetous orders: 1) most of the examined species from the sections Acremonium, Gliomastix, and Nectrioidea showed a relationship to the Hypocreaceae even though many of these species have never been asso- ciated with any teleomorph; 2) the grass endophytes of sect. Albolanosa and other taxa from the Clavicip- itaceae formed a monophyletic group derived from within the Hypocreales; 3) the thermophilic A. ala- bamense of sect. Chaetomioides was derived from with- in the Sordariales. Acremonium alternatum, the tye species of the genus, was one of the species showing affiliation to the Hypocreaceae. In order to eliminate some of the heterogeneity within Acremonium while also emphasizing the unique biological, morpholog- ical, and ecological characteristics of the grass en do-