Using petiole anatomy to identify hybrids between and species of Populus sections Aigeiros and Tacamahaca

The article presents the results of the study of the petiole anatomy peculiarities of the hybrids between Aigeiros and Tacamahaca sections. Petiole anatomic structure was found to be helpful in assigning taxa to a section and to find intersectional hybrids, which is actual for studying populations in natural and anthropogenic hybridization zones. Cross sections made in the upper part of petioles were used for analyzing anatomic traits by light microscopy. All representatives of the Aigeiros section have linear form of the vascular system, consisting of 3–5 rings, with a rounded contour of the petiole adaxial side. In the Tacamahaca section taxa the vascular system is highly arched, and the adaxial side is cordate. The study of the hybrids between species of the same section revealed that such hybrids inherit anatomy features common for the section. We can consider such traits as adaxial side shape and vascular system type to be the most important markers for intersectional hybrids. Truncated or notched shape of the adaxial contour and vascular system type were found to be characteristic features of hybrids, as small notches in their petioles’ upper part are common for all hybrids. Most of hybrids have small notches, rather than grooves, in the upper part of their petioles. Most of the intersectional hybrids have transitional shape of vascular system. The anatomy of Populus × sibirica petioles confirmed earlier results that it is a hybrid cultivar, that originated as a result of crossbreeding between Aigeiros and Tacamahaca section species.