CONTENTS

Section Sideritis is an extremely diversi®ed group which is formed mainly by species growing at low altitude. The group of high altitude taxa of this section is polyphyletic and has been taxonomically divided in diVerent subsections in which these taxa appear normally associated with low-lying planitiary ones, the latter being the probable ancestors. The subsections comprising high altitude taxa are: subsect. Gymnocarpae, subsect. Fruticulosae; subsect. Hyssopi-foliae, subsect. Luridae; subsect. Borgiae and subsect. Aranensis. Most of the high altitude taxa of section Sideritis are endemics with small distribution areas; they are incompletely known and threatened with extinction. The upper altitude limit of this section is attained at over 3000 m in Sierra Nevada (Spain) by Sideritis glacialis Boiss., which has been included in subsect. Fruticulosae OboÂn and D. Rivera. The taxonomy of this complex group of high altitude endemic taxa of Sideritis subsection Fruticulosae is discussed on the basis of macro-morphological and micro-morphological characters. These are used in identi®cation keys and for analysis of dissimilarity. The diVerent habitats, allied species and plant communities are described. The following taxa are recognized: Sideritis glacialis subsp. glacialis, S. glaciali