Mediterranean gall oaks, Quercus subsection Galliferae

Trichome characters are often considered to be taxonomically important in oak species. In this article, we investigate a group of Mediterranean oaks, Quercus subsection Galliferae and Q. pubescens, using a large dataset and covering the entire distribution range of the group. As a result of the different interpretations of terms in previous studies, trichome terminology was re-assessed aiming to obtain a practicable nomenclature. In contrast with previous studies, we found that acicular, bifurcate, fasciculate, stellate, uniseriate and capitate trichomes are represented in all taxa. One exception is the lack of bifurcate trichomes in Q. canariensis. This suggests that seemingly taxonomically informative presence/absence data for trichome types, as reported previously, may be the result of too small a sample size, and this may be unrepresentative. In combination with other morphological characters (leaf shape, size and texture), features of the indumentum, such as the floccose, easily removable trichomes in Q. canariensis, can be important in species delimitation. The use of trichome characteristics in Quercus subsection Galliferae requires exhaustive sampling of all taxa in order to extract a reproducible taxonomic signal from quantitative characters. This is the prerequisite for building datasets that can be used for phylogenetic analyses, investigations of character evolution and comparative morphological studies.