Comparative leaf anatomy of Stachys (Lamiaceae: Lamioideae) in Iran with a discussion on its subgeneric classification

Stachys (Lamiaceae: Lamioideae) is a species-rich, widespread, and taxonomically complex genus. A comparative anatomical study of the petioles and leaf lamina of 34 Stachys taxa representing 12 sections of the genus distributed in Iran was carried out to evaluate interspecific relationships and anatomical features that may be useful in species identification and subgeneric classification. The general leaf anatomy of Stachys species presented here corroborates earlier studies in Lamiaceae and on a few studied species in the genus. Leaf anatomy provides valuable characters that are useful in subgeneric classification as well as species discrimination in Stachys. The most important diagnostic characters are as follows: the shape of transverse section, length of ventral and dorsiventral axis, number of median bundles in the petiole, number of cell layers of palisade and spongy parenchyma, type and thickness of collenchyma as well as trichome type. Based on the present study and in accordance with previous works, some large sections such as Ambleia, Aucheriana, and Fragilicaulis appear to be natural and need minor or no changes in delimitation, while circumscription of sect. Olisia should be revised. Isolated positions of some monotypic or oligotypic sections, such as Pontostachys, Thamnostachys, and Trinerves, as well as Zietenia, are supported by unique leaf anatomical features.