Morphological features of seedlings and juvenile plants of some Pyrus L. (Rosaceae) representatives in connection with their systematics

Abstract

A study of early stages of ontogeny of the species Pyrus caucasica Fed., P. georgica Kuth., P. medvedevii Rubtzov, P. oxyprion Woronow, P. salicifolia Pall., P. sosnovskyi Fed., P. zangezura Maleev was conducted. A morphological description of seedlings and juvenile plants, as well as an overview of their morphological features were done. It was clarifi ed that some structural features of cotyledons, of the fi rst (two or three) leaves of seedlings, juvenile leaves, petioles, stipules can be used as taxonomical ones on the species and sectional levels of the genus. During the transition from seedlings to juvenile and adult plants an early unifi cation of the shape of leaves, as well as differentiation of two or three intermediate heterophyllous leaves series are observed. In some cases the analysis of the heterophylly of juvenile plant leaves can be a source of information about the formation processes in Pyrus genus. Data obtained in our research do not deny the existing ideas about the possible monophyletic origin of the genus Pyrus, but at the same time they favor the early divergence of several groups of pears, represented in the modern taxonomical system of the genus by sections, the differences of which appear already on the stages of seedlings and juvenile plants.