The zygomycete genus Lichtheimia (syn. Absidia pro parte, Mycocladus) consists of saprotrophic fungi inhabiting soil or dead plant material. Lichtheimia corymbifera (syn. Absidia corymbifera, Mycocladus corymbifer) and Lichtheimia ramosa (syn. Absidia ramosa, Mycocladus ramosus) may cause fulminant infections in patients with impaired immunity. The present study investigated the species boundaries in Lichtheimia using genealogical concordance phylogenetic species recognition (by comparison of the genealogies of the internal transcribed spacer [ITS] sequence, the D1/D2 region of the large subunit [LSU], and actin), biological species recognition by mating tests, as well as morphological and physiological characteristics. The three molecular markers used were selected by evaluating the polymorphisms and paralogies of several loci, including those for -tubulin, translation elongation factor 1␣, the two largest subunits of the RNA polymerase II (RPB1 and RPB2), the mitochondrial cytochrome c oxidase subunit I (COI), and the mitochondrial small-subunit (mtSSU) rDNA, among four strains belonging to different putative species. Comparing the genealogies of the ITS, LSU, and actin genes, we recognized seven phylogenetic species. However, mating tests did not show intrinsic reproductive barriers for two pairs of the phylogenetic species. Therefore, we regard five species in Lichtheima to be confirmed: Lichtheimia corymbifera, L. ornata comb. nov., L. ramosa, L. hyalospora, and L. sphaerocystis sp. nov. Only the first three species seem to have clinical relevance. Lichtheimia blakesleeana is reduced to a synonym of Lichtheimia hyalospora. We provide a detailed description of Lichtheimia sphaerocystis sp. nov. and a key for the identification of all accepted species identified in the present study on the basis of their morphological traits and growth at different temperatures.Mucormycoses, i.e., infections caused by members of the Mucoromycotina subphylum, are uncommon but often dramatic, requiring immediate action on the basis of an accurate diagnosis. The recently observed increase in case reports on mucormycosis (32) can be ascribed to the growing number of patients with risk factors, such as diabetes, neutropenia, bone marrow transplantation, and the long-term use of steroids. Although this trend was already observed prior to the availability of voriconazole in medical applications (17, 21), several studies related the increasing incidence of mucormycoses to voriconazole prophylaxis and treatment of aspergillosis infection in immunocompromised patients (18,37,43). According to Roden et al. (32), approximately 5% of cases of mucormycoses are caused by species of Lichtheimia (syn. Absidia pro parte [p.p.], Mycocladus). These authors reviewed 25 well-documented cases of Lichtheimia (as Absidia) infections that have occurred since 1940. However, the actual incidence of the species may have been underestimated, given the fact that no less than 53 clinical Lichtheimia strains were sent to the CBS Fungal Biodiversity Centre (...