Phylogenetic significance of leaf micromorphology and anatomy in the tribe Mentheae (Nepetoideae: Lamiaceae) HYE-KYOUNG MOON 1 *, SUK-PYO HONG FLS 2 , ERIK SMETS FLS 1,3 and SUZY HUYSMANS 1 1 Laboratory of Plant Systematics, Institute of Botany and Microbiology, K.U. Leuven, Kasteelpark Arenberg 31, PO Box 2437, BE-3001 Leuven, Belgium 2 Laboratory of Plant Systematics, Department of Biology and Institute of Global Environment, Kyung Hee University, Seoul 130-701, South Korea 3 National Herbarium of the Netherlands, Leiden University Branch, PO Box 9514, NL-2300 RA Leiden, The Netherlands Received 25 December 2008; accepted for publication 1 April 2009 A comparative micromorphological study of leaves was carried out on 102 species of Mentheae; 61 species were selected for the anatomical study. Mentheae possessed both amphistomatic and hypostomatic leaves. The diversity of leaf epidermal characteristics was based on the variation in morphology of epidermal cells, stomata types and trichome types. Although each characteristic on its own has rather limited systematic value, the combination of some of these features may be systematically relevant, especially for the identification of species. For example, branched multicellular nonglandular trichomes were a diagnostic characteristic for all genera investigated of the subtribe Salviinae; however, this trichome type was also observed in Hedeoma ciliolata and Neoeplingia leuco- phylloides of the subtribe Menthinae. Capitate glandular trichomes with pear-shaped heads were only observed in Salvia dorrii. Subsessile glandular trichomes with multicellular heads (more than ten cells) were an apomorphy for Perovskia. The anatomical leaf structure was consistent throughout the tribe. In some species, the vascular bundles in the midrib were modified into a mechanical tissue, which is an adaptation to xerophytic environments. The observed variations are discussed in an ecological context and their phylogenetic significance is evaluated. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160, 211–231. ADDITIONAL KEYWORDS: epidermis – phylogenetics – stomata – systematics – trichome – vascular bundle. INTRODUCTION Lamiaceae (Lamiales, euasterids I; APG II) are rich in herbs and medicinal plant species, which are of great economic importance. Lamiales formerly had a restricted circumscription that included the families Lamiaceae, Verbenaceae, Boraginaceae and Len- noaceae (Cronquist, 1988), but recent phylogenetic work has shown that Lamiales is monophyletic with the inclusion of former orders Bignoniales, Hippurid- ales, Plantaginales and Scrophulariales (Stevens, 2001; Judd et al., 2008). Consequently, Lamiales has become one of the larger angiosperm groups, contain- ing about 12% of the eudicot diversity (23 families with 1059 genera and 23 275 species; Stevens, 2001). Lamiaceae has a cosmopolitan distribution and con- sists of 236 genera and about 7000 species (Stevens, 2001). Many species of Lamiaceae produce essential oils which are secreted by glandular hairs on aerial vegetative organs and some reproductive organs. These hairs have been investigated from structural, ultrastructural and biochemical viewpoints for their commercial value in various members of the family (Amelunxen, 1964, 1965; Amelunxen, Wahlig & *Corresponding author. E-mail: hyekyoung.moon@bio.kuleuven.be Botanical Journal of the Linnean Society, 2009, 160, 211–231. With 6 figures © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160, 211–231 211