The genus Odontarrhena in Albania: disentangling the systematics of a critical group of Ni-hyperaccumulators in a European serpentine hotspot

Among the angiosperm groups including Ni-hyperaccumulator species in the Euro-Mediterranean region, Odontarrhena C.A.Mey. is the most important in terms of diversity and distribution range. Based on present-day knowledge, all species in this genus that grow on serpentine soils are able to accumulate more than 1000 μg Ni g−1 leaf dry weight without toxicity symptoms. Several experimental studies on the physiological and molecular mechanisms of metal hyperaccumulation have been performed on model taxa of this genus, and many of these have been used or considered for phytoremediation or phytomining practices. Despite the importance of such plants, our knowledge about diversity and systematics of Odontarrhena C.A.Mey. is still incomplete and affected by considerable uncertainties. Taxonomic interpretation of several species groups remains problematic due to the often large phenotypic plasticity of populations, weak correspondence between morphological, ecological or geographical variation, low phylogenetic divergence and relatively homogeneous karyotype features. Past authors who focused on the Euro-Mediterranean members of this genus proposed complex treatments based on a narrow morphological species concept. More recent views mostly recognize a lower number of taxa, that, however, are considerably different from author to author. Nomenclatural inconsistencies caused by the divergent taxonomic opinions hamper further studies of ecological and physiological type, as well the use of these plants for practical applications. Because of the large occurrence of serpentine soils, Albania is a major center of diversity of Odontharrhena. However, no consensus still exists even about the number and the distribution of native taxa, as well as on the names to be adopted for them. Patterns of genetic variation and diversity within and between such taxa/populations are also unknown. Accordingly, we started a systematic investigation mainly based on data collected from over twenty natural populations from the entire national territory. After a thorough analysis of the available taxonomic literature and herbarium specimens, including type collections, we collected and sampled plant material from the type localities of the numerous taxa described from the country. Additional sampling will be performed in summer 2017. The material is currently under investigation with morphological, karyological and molecular methods, to address the following questions: 1) how many and which taxa (species and subspecies) can be reasonably recognized from Albania? 2) what are their phylogenetic relationships and patterns of population genetic structure and diversity? Finally, the Ni-hyperaccumulation capacity in relation to population morphological and genetic characters is also under investigation, to get insights on the most promising accessions for phytoremediation and/or phytomining applications.