Systematic significance of anatomy and trichome morphology in Lamium (Lamioideae; Lamiaceae)

Lamium (Lamiaceae, Lamioideae) is a widespread and taxonomically complex genus. A comparative anatomical study of the root, stem, leaf and petioles in 33 taxa assigned to this genus is carried out in order to address generic delimitation, subgeneric classification and species delimitation. Using light and scanning electrone microscopy, anatomical features and indumentum characteristics are investigated. In addition, the phylogenetic implication of the observed variations are discussed. Anatomical characters of taxonomic interest are as follows: the presence or absence of collenchyma at the corners of stems and petioles, the number of pith rays in the root, shape of the vascular bundles in petioles and characteristics of leaf mesophyll. Non-glandular trichomes can be short or long, while the glandular trichomes are stalked, subsessile or sessile. The indumentum is taxonomically significant, particularly in discrimination of taxa in "L. garganicum complex" and their delimitation from L. armenum. Trichome characters are also important in distinguishing the alpine Turkish endemic L. eriocephalum from other taxa in L. sect. Amplexicaule. Our analyses partly corroborate the findings of recent phylogenetic investigations and support also partly the current infrageneric classification of the genus. Anatomical features and trichome characters reject accepting Galeobdolon and Wiedemaniana as distinct genera. In general, Our investigations reveal the usefulness of such characters in taxon delimitation at various ranks, especially at the specific and partly at the sectional level. (C) 2016 Elsevier GmbH. All rights reserved