Format: ORAL

David Horcajada1,Beln Estbanez2, Rafael Medina3

1 Universidad Pablo de Olavide. Sevilla, Spain. 2 Universidad Autónoma de Madrid. Madrid, Spain. 3 Universidad Complutense de Madrid. Madrid, Spain.

Complex thalloid liverworts (class Marchantiopsida) represent a good example of the importance of microanatomical characters when the macroscopic ones fall short in taxonomic decisions. Some representative microscopic structures showing traits with taxonomical relevance in the group include dorsal epidermis cells, dorsal papillae, hairs, air pore cells, photosynthetic filaments, scales, or rhizoids. Dumortiera hirsuta (Sw.) Nees is a widespread pantropical species present also in some temperate regions, characteristically lacking some typical complex thalloid traits, such as air pores or a developed epidermic reticulum. This liverwort displays, nonetheless, a remarkable variation of other microscopic traits. This fact led 18th and 19th-century botanists to describe multiple species that were later synonymized to D. hirsuta, concurrently with the lumping trend that thalloid liverwort taxonomy experienced throughout the 20th century. Recently, the likelihood of the ancient multiple-species hypothesis is again being reconsidered according to molecular data. We have chosen this liverwort as a model to study the importance of microscopic characters in Marchantiopsida systematics. For that purpose, the presence or absence of epidermal papillae, the vestiges of epidermal reticulum (in the form of vertical walls on the dorsal epidermis), the morphology of hairs and rhizoids, as well as the morphology and ornamentation of spores, were studied in a selection of D. hirsuta specimens, mainly from Europe, Macaronesia, and the Americas. The integration of the morphoanatomical and newly generated molecular data, which is coherent with the multiple-species hypothesis, is discussed together with the next steps to improve our understanding of this lineage.