<i>Euphorbia</i> L. subsect. <i>Esula</i> (Boiss. in DC.) Pax in the Iberian Peninsula. Leaf surface, chromosome numbers and taxonomic treatment

Abstract

We present a taxonomic study of the representatives or Euphorbia subsect. Esula in the Iberian Peninsula. Prior to this, a first section is included on the study of the leaf surface and a second section on chromosome numbers. The section on leaf surface is based on a study of the leaves or 45 populations of Iberian and European taxa of the subsections using a light microscope and SEM. The characters analyzed are cell shape, morphology of the cells and stomata (primary and secondary sculpture) and epicuticular waxes (tertiary sculpture). Some microcharacters of the leaf surface proved particularly usefu1for taxonomical purposes. Thus the basic type of stoma and the distribution model of the stomata on the two sides of the leaf are characters which make it possible to separate taxa as closely related as E. esula L. subsp. esula and E. esula L. subsp orientalis (Boiss. in DC.) Molero & Rovira. The morphological type of the epicuticular waxes also enables us to differentiate between E.graminifolia Vill. and E. esula aggr. And to distinguish subsp. bolosii Molero & Rovira from the remaining subespecies in E. nevadensis Boiss. & Reuter. Cytogenetic investigation reveals the presence of only the diploid cytotype (2n=10) in E. cyparissias L. and E. esula L. subsp. esula in the Iberian Peninsula. We describe for the first time in E. nevadensis s.1. a polyploidy complex with a base of x= 10 in which the diploid level (2n=20) is present in all subspecies; the tetraploid level (2n=40) is present in E. nevadensis subsp. nevadensis and the hexaploid level (2n=60) is found in E. nevadensis subsp. bolosii . Chromosome number is not a parameter that can be used for taxonomic purposes. In E. nevadensis , cytogenetic differentiation has followed its own course, with no apparent relationship to the process of morphological differentiation. Our final taxonomic treatment aims to achieve coherence with the result of the study of the leaf surface and the micromorphology of the seeds, taking into account those characters that are of use. In this section we include aspects related to nomenclature and typification, descriptive characters, keys, ecology and geographical distribution. We describe a new taxon: E. nevadensis Boiss. & Reuter subsp. bolosii Molero & Rovira; we establish the new combination E. esula L. subsp. orientalis (Boiss. in DC.) Molera & Rovira. E. sennenii Pau is considered a synonym of E. nevadensis Boiss. & Reuter subsp. aragonensis (Loscos & Pardo) Bolos & Vigo.