Foliar diagnostic characters in Iberian species of Isoetes L. (Isoetaceae, Pteridophyta)

Abstract

This is a comparative study of foliar morphology of the species of Isoetes L. growing in the Iberian Península. The taxa included are /. durieui and /. histrix (terrestrial), /. setaceum, and /. velatum subsp. Velatum (amphibious), and /. brochonii, I. echinosporum, I. x hickeyi, I. lacustre, I. longissimum and /. velatum subsp. Asturicense (aquatic). Material of an undescribed amphibious tetraploid taxon related to /. velatum was also included in this study and referred as Isoetes sp. until proper description. Several Iberian collections, together with European and American specimens of some of the taxa were analyzed. Selected diagnostic characters of the microphylls are: cuticular ornamentation (striae, ridges and warts), cuticular flanges, epidermal patterns, stomata distribution and dimensions, foliar transverse sectíons outline, degree of development of the mesophyll, presence or absence, and distribution of the mechanical tissues (collenchyma), diaphragms, and presence or absence and type of intercellular pectic protuberances. All characters are stable, and do not vary with the age of the plants or the microphylls. Cuticular striae, ridges and warts, as well as stomata develop early in plantlets. Stomata present in the microphylls of two aquatic taxa (/. longissimum, I. velatum subsp. asturicense) suggest that their absence is not entirely due to influence of aquatic environment. Collenchyma occurs, also, in species growing in different habitats. Restored herbarium material proved to be as useful as fresh or fixed material, an important advantage in the case of Isoetes species, many of which grow in vulnerable áreas or are known only through herbarium specimens due to destruction of their pristine habitats.