Taxonomy of origanum L. (Lamiaceae)

Origanum (Subfamily Nepetoideae, tribe Mentheae, subtribe Menthinae) contains several species commonly used as spices, tea, and for medicinal purposes, and is one of the most commercially important genera within the family Lamiaceae. Origanum is found exclusively in the Northern Hemisphere of the Old World, with 90% of the taxa occurring in the Mediterranean region. Although members of the genus are predominantly distributed in the Mediterranean region, there are also species (e.g., O. vulgare s.l.) distributed from the Azores to Taiwan and throughout much of Eurasia. Diploid chromosome numbers have been reported as 2n = 28, 30 and 32, with the basic number x = 15. Hybridization is quite common (~52% of species) within Origanum, and can occur between individuals belonging to the same or different generic sections. Homoploid hybridization appears to be the primary ploidy mechanism within the genus. Here, we define Origanum as having 42 species (49 taxa) and 22 hybrids, and provide an updated sectional delimitation of the genus. In addition to providing taxonomic clarification, information including gross morphological characters, photographs and drawings, distribution, ecology, and cytology of the genus are also provided.