EUROPEAN AND MEDITERRANEAN OAKS (QUERCUS L FAGACEAE) - SEM CHARACTERIZATION OF THE MICROMORPHOLOGY OF THE ABAXIAL LEAF SURFACE

This paper examines micromorphological characteristics (trichomes, wax es, stomata) of the abaxial leaf surface of European and Mediterranean oaks. Observations were performed by scanning electron microscopy; an d the purpose of the investigation was to ascertain whether it is poss ible to distinguish the different species taxonomically using these fe atures. Several species. as well as some subspecific entities and taxa considered doubtful, were taken into consideration. Subgenera appear to be well-defined: e.g. the subgenus Quercus is characterized by waxe s arranged in vertical scales: the subgenera Cerris and Sclerophyllodr is by smooth waxes. They differ because the former has markedly ellipt ical stomata, while the latter two have roundish stomata. The differen t species are also fairly easy to distinguish, and this fact confirms the taxonomical validity of the parameters we have taken into consider ation. In some casts subspecific entities and doubtful species do :lot differ at all from the related species, but ill others they present s uch marked variations that it is difficult el-en to classify them with certainty. The most critical taxonomic groups (i.e. those which inclu de a number of specific and subspecific entities often too difficult t o distinguish from each other) are the series Quercus robur - Quercus petraea - Quercus pubescens and the Quercus faginea - Quercus lusitani ca - Quercus canariensis group. (C) 1997 The Linnean Society of London .