Pericarp structure and phylogeny of tribe Mentheae (Lamiaceae)

Pericarp structure is investigated in 143 specimens belonging to 59 out of ca. 65 genera and 134 out of ca. 2,000 species of Lamiaceae subfamily Nepetoideae tribe Mentheae. Some of the data presented by earlier authors are believed to be incorrect. The variation in pericarp structure has been found to be strongly correlated to the variations in DNA and gross morphological characters. The groups of two-staminate genera (Salvia, etc.) and four-staminate genera of Salviinae (Lepechinia and Chaunostoma) can be distinguished from each other and from other labiates by differences in pericarp structure. The other two subtribes, Menthinae and Nepetinae, differ considerably, but their variations strongly overlap. The differences in pericarp structure also suggest that Menthinae can be divided into three main monophyletic groups based on other data: (1) the main bulk of the tribe, (2) a group of Prunella and Cleonia and perhaps also Horminum, and (3) the characteristic genus Lycopus. Pericarp data disagree with a suggestion that the genus Melissa should be included in the subtribe Salviinae. Modifications of the subtribal classification of Mentheae are discussed.