Herbarium investigations: a tool to to solve taxonomic and phylogenetic problems.

Taxonomy has originally been based on morphological features. In the last two decades the use of DNA barcoding has enabled the identification of new species and the systematics of many groups. This has been extended also to photosynthetic organisms, such as cyanobacteria, microalgae, seaweeds, and plants. In fact, for the high degree of morphological plasticity exhibited by many members of these taxa, several characters traditionally considered diagnostic have revealed ambiguous and accordingly useless. Type specimens, on which names of species are based, are necessary for comparison in systematic studies, as stated by the International Code of Botanical Nomenclature. Unfortunately, very often the types are lacking, or are illustrations, which are not suitable for modern systematics. In other case, however, herbarium types are still available. Recently, molecular techniques have developed to extract DNA and to amplify molecular markers also from historical material, making herbaria a precious source of information, as attested by several studies ranging from taxonomy to phylogeography and ecology. In the light of this, the herbarium collection of the University of Padua (Italy) can play an important role in modern researches on biodiversity, systematics, and phylogeny.