Ocimum L. is a genus within the Labiatae, which contains several spices and medicinal herbs. The economically most important species are O.basilicum, O.minimum, O.americanum and the hybrid O. x citriodorum, which are used for essential oil production and as pot herbs. Species number is estimated between 30 and 160. A recent revision of the genus based on morphology and cytology described 65 species native in the tropical areas of America, Africa and Asia (Paton et al. 1999, in: Hiltunen and Holm Basil: the genus Ocimum.) Some species were placed into synonymy, and the genera Erythroclamys, Becium and Orthosiphon subgen. Nautochilus were incorporated into the genus Ocimum. Recently also the genus Plectranthus is suggested to be part of Ocimum. To assess phylogenetic relationships of Ocimum and related genera, the morphological hypothesis was tested with an analysis of nrDNA internal transcribed spacer sequences (ITS). Cladistic and phenetic analyses resulted in a paraphyletic genus Ocimum with Plectranthus, Aeollanthus, Catoferia, and Pycnostachys grouping within Ocimum. Plectranthus is a monophyletic sistergroup of subg. Nautochilus, Aeollanthus, which morphologically resembles Plectranthus,is part of section Gratissima. Most morphologically defined sections of Ocimum could be confirmed by the molecular analysis. However, O.minimum, often considered as a subspecies of Ocimum basilicum, is not conspecific with O.basilicum and even groups outside of section Ocimum.

Key words: ITS, Lamiaceae, Ocimum, phylogeny