Identification of Populus nigra, P. laurifolia and P. × jrtyschensis by leaf petiole anatomy

Remarkable variability in morphology of the Populus genus, as well as widely spread hybridization within the genus complicate taxa identification. Petiole anatomy plays an important role in plant taxonomic attribution and resolution of arguments in systematics. The aim of the study was to examine the petiole anatomy of P. nigra, P. laurifolia and P. × jrtyschensis to assess its potential use for taxa identification. The leaf petioles were collected from 252 individual trees in 8 populations of P. nigra, P. laurifolia and P.× jrtyschensis in the area of their natural hybridization in the basin of the Tom River in Kemerovo Oblast. Two of those 8 populations, located far from the hybridization centers, were regarded as controls to characterize parent taxa. Cross sections were made in the upper part of petioles. Then the sections were used to examine the shape of petiole cross sections, the contour of the adaxial sides, the vascular system types and lower ring shape. The petioles of trees growing far from hybridization areas were found to differ in their vascular systems: P. nigra had a linear, while P. laurifolia a high­arc­shaped one. The hybrids were found to belong to several types of vascular systems, namely intermediate, high­intermediate, linear and high­arc­shaped ones. The intermediate type of vascular system is characteristic of the most part of P. × jrtyschensis trees (78 % of the total samplings). Therefore most of them can be classified as F1 hybrid and others – as a recombinant species. Examination of P. nigra in its natural hybridization center allowed finding an approach to the identification back­crosses. The study confirmed provides a solid basis for the identification of parent species, hybrids and backcrosses in natural hybridization areas of taxa belonging to Aigeiros and Tacamahaca sections of Populus genus.