Leaf architecture and anatomy of Tilia L. (Malvaceae)

Background and Aims: Systematic anatomy and leaf architecture have supported the separation of species by using leaf morphological and anatomical characters, such as, the arrangement of vascular bundles or the venation pattern. The genus Tilia (Malvaceae) consists of approximately 23 species with unclear boundaries between some of them. Methods: The purpose of this work was to identify leaf morpho-anatomical characters that contribute to Tilia species differentiation. Leaves of eight species and four subspecies were collected studied. Leaf architecture was described using herbarium voucher and cleared-leaves and leaf anatomy through transverse and paradermal sections. Key results: Results showed that leaves are variable in shape, margin dentate with first and second order teeth, secondary venation mostly craspedodromous and well-developed areole. Leaves were hypostomatic heterobaric and with three types of midvein. The combination of characters favored the recognition of species. For example, T. platyphyllos is characterized by teeth with narrower bases, T. mongolica is the only species with a deltoid lamina and without domatia and T. caroliniana subsp. occidentalis is separated by lamina with three teeth per cm and four-armed stellate trichomes with a length of 296 µm. Conclusions: The different combinations of leaf characters are promising for the systematics of the genus Tilia.