M.Sc. (Botany) / The genus Phomopsis is an important fungal genus due to its widespread pathogenicity on a wide variety of hosts and its complex anamorphic morphology. Three species of the genus Phomopsis viz. Phomopsis citri, Phomopsis leptostromiformis and Phomopsis zeicola, were studied in artificial culture and on host plants in vitro. The culture of Phomopsis citri failed to form conidiomata in culture and this species was studied intensively. As the species in this genus are difficult to distinguish and identify, the species named above were compared in an attempt to define taxonomically usable distinguishing characters. The morphology and ontogeny of the colonies, conidiomata and conidia, the karyology of these species, pathogenicity to cultivars of Lupinus spp. and Zea mays, were studied and the pectic enzymes were analyzed. Optical-, scanning electron- and transmission electron microscopic techniques were used in addition to the enzyme analysis. The conidiomata were typically stromatic and often irregularly multiloculate and could arise from more than one type of primordium. The most common primordia were ringshaped structures but hyphal aggregations were also found. Conidiogenesis was phialidic and the a-conidia of both species examined were shown to be uninucleate. The {3-conidia of Phomopsis leptrostromiformis were similarly uninucleate but failed to germinate. Their function is thus still unknown. Phomopsis zeicola failed to form {3-conidia. Transmission electron microscopy showed differences in conidial morphology between these species which, together with pectic enzyme analysis, could be good characters to separate species in this genus. The implications of heterokaryosis are discussed in assessing the potential value of these parameters and further investigations will have to be done.