Trichoderma harzianum is a ubiquitous species in the environment and is effective in the biological control of plant-pathogenic fungi. T. harzianum has not been linked unequivocally to its sexual state nor has its phylogeny been studied in detail. It has been suggested that T. harzianum is a species complex based on the phenotypic and genotypic variability encountered. On the basis of morphological and cultural characters and DNA sequence data analysis of four genes (ITS rDNA, translation elongation factor 1-alpha, calmodulin, and alpha-actin), Hypocrea lixii was found to be the sexual state of T. harzianum. Both the asexual and sexual states of this species have wide geographic distributions. Phylogenetic analysis of four genes showed that T. harzianum/H. lixii is a cohesive group that is supported by bootstrap values higher than 95%. Principles of genealogical concordance indicated that T. harzianum/H. lixii is a complex of independent monophyletic lineages, but no diagnostic morphological distinctions were identified that justify formal taxonomic recognition for the different lineages.