Thesis (MSc (Microbiology))--Stellenbosch University, 2008. / Penicillium is a well‐known cosmopolitan genus with more than 225 accepted species. Species from this diverse genus, in general, are considered to primarily be soil fungi, with decomposition as its main function. Therefore, together with its ubiquitous nature, these species are of great importance in ecosystems, agriculture and biotechnology. However, in South Africa, very little research has been done on this complex genus, as species identification were often found to be problematic, even for experienced taxonomists. This lead to a number of South African studies only mentioning that a Penicillium spp. were isolated, without making any attempt of showing the extent of diversity within the genus from the unique habitats. The present study set out to explore the extent of the species diversity in Penicillium isolated from the Cape Floristic Region, specifically focusing on coastal fynbos soil. Soil samples were collected from this region, at sites situated outside Malmesbury. Four hundred and thirty four Penicillium strains were isolated from soil‐dilutions. The strains were characterized using morphological characters and subsequently placed into 24 morphological groups. There were, also, more or less 40 strains that could not be grouped with any other isolates. Groupings were made according to conidiophore branching patterns which divided the strains into their respective subgenera. Eight species from subgenus Aspergilloides, seven from subgenus Furcatum, eight from subgenus Biverticillium and one from subgenus Penicillium were isolated. The species were further characterized in subsequent chapters. In the second chapter of this thesis, one of the taxonomic groups in subgenus Biverticillium, isolated from coastal fynbos soil, Protea infructescences and on moth‐damaged Riesling grapes in Canada, was examined. This species was characterized using morphology and were found to have several unique characters, such as the very short synnema produced after prolonged incubation. These characters did not conform to descriptions of previously described species. Its novelty was confirmed by an ITS phylogeny and the strains were subsequently described as Penicillium ramulosum prov. nom. with P. cecidicola and P. dendriticumas its sister taxa. In chapter three, a further seven groups belonging to Penicillium subgenus Biverticillium were characterized. These strains were identified as P. minioluteum, P. verruculosum and P. rugulosum‐like, respectively. Four of the groups showed unique morphological characters, with the ITS phylogeny resolving the fynbos strains separate from all previously described species. The strains were, therefore, considered to be new to science and described as P. solicola prov. nom., P. ptychoconidium prov. nom., P. occultum prov. nom. and P. chloroloma prov. nom., respectively. A key to species from subgenus Biverticilliumcluded. is also inPenicillium subgenus Furcatum was the subject of the fourth chapter of this thesis. Our survey found that although the species diversity in this group was not as high as for the other subgenera, it was the group most often isolated in this study. Species were identified as P. janczewskii, P. canescens, P. melinii, P. corylophilum and P. citrinum using morphological characters. One species belonging to subgenus Penicillium, P. expansum, was also isolated and compared to species recorded during a previous survey. Amongst the identified species, were two groups that could not be identified using published keys, with their novelty confirmed by an ITS phylogeny. They are, therefore, described here as P. subturcoseum prov. nom. and P. hemitrachum prov. nom. A key to species in this subgenus is also provided. In Chapter 5 the presence of Penicillium subgenus Aspergilloides, which is characterized by monoverticillate conidiophores, were investigated. Species were identified as P. roseopurpureum, P. restrictum, P. hirayamae and P. toxicarium. Amongst the identified species, were four groups that did not conform to previously described species and are described here as P. brachycaulon prov. nom., P. malacosphaerula prov. nom., P. cumulacinatum prov. nom. and P. vulgaris prov. nom., respectively. The newly described species have been included in a key, together with closely related species and the other species of subgenus Aspergilloides from the fynbos soil. Species identifications in Penicillium is often problematic and South African taxonomists have often not attempt to identify strains down to species level. During this study, Penicillium was found to be well represented in the soil, with a large proportion being previously undescribed. For this reason, a dichotomous and synoptic key to species isolated during this study are provided in the final chapter. This study should thus serve as a basis for further explorations into the diversity and ecological role of this group of organisms in this ecologically mportant biome.