New annotated checklist of the Portuguese oaks (Quercus L., Fagaceae)

We present a comprehensive taxonomic and nomenclatural review of the Portuguese oaks (Quercus L.), issuing from throughout biogeographical, historical, bibliographic, field and herbarium data. We propose a new annotated checklist for all taxa and nothotaxa belonging to Quercus L. genus in the Portuguese national territory, extending the analysis to the broader biogeographical context of Western Mediterranean Subregion. Fifteen herbaria collections were exhaustively studied and complemented by information retrieved from digital collections, resulting in the recognition of eleven native oaks. Further treatment at infraspecific level includes one subspecies and additional 23 nothotaxa. We designate 21 names as types and add a preliminary list of 150 cultivated trees, concurring to a total of 185 oak taxa, in total, found in Portugal. Moreover, we clarify the taxonomical status and reinstate both Quercus calliprinos Webb and Q. pseudococcifera Desf. as native for the Western Mediterranean subregion. We recover the concept of Q. faginea Lam., as the widespread Gall oak in Portugal and update its synonym list. We propose Q. broteroana and Q. estremadurensis as autonomous species within the European Q. robur s.l. broad group, alongside two newly circumscribed subsections inside Section Quercus. We describe three nothotaxa as new (Q. ×alvesii, Q. ×capeloana and Q. ×sampaioana) and approach the nomenclatural resolution of the remaining natural hybrids. Lastly, we provide an identification key, intelligible for non-specialists, including both native taxa and most frequent nothotaxa. We emphasise the importance of historical and literature review, combined with accurate biogeographical information, as paramount to coherent taxonomical resolution. Both specimens and their associated records were found of crucial significance to a taxonomical model that is, in the end, useful to biodiversity conservation.