No taxon left behind? – a critical taxonomic checklist of Carpinus and Ostrya (Coryloideae, Betulaceae)

Hornbeams (Carpinus) and hop-hornbeams (Ostrya) are trees or large shrubs from the northern hemisphere. Currently, 43 species of Carpinus (58 taxa including subdivisions) and 8 species of Ostrya (9 taxa including sudivisions) are recognized. These are based on 175 (plus 16 Latin basionyms of cultivars) and 21 legitimate basionyms, respectively. We present an updated checklist with publication details and type information for all accepted names and the vast majority of synonyms of Carpinus and Ostrya, including the designation of 54 lectotypes and two neotypes. Cultivars are listed if validly described under the rules of the ICN. Furthermore, we consider Carpinus hwai Hu & W.C.Cheng to be a synonym of Carpinus fargesiana var. ovalifolia (H.J.P.Winkl.) Holstein & Weigend comb. nov. During the course of our work, we found 30 legitimate basionyms of non-cultivars that have been consistently overlooked since their original descriptions, when compared with the latest checklists and floristic treatments. As regional floras are highly important for taxonomic practice, we investigated the number of overlooked names and found that 78 basionyms were omitted at least once in the eight regional treatments surveyed. More seriously, we found 4 basionyms of accepted species being overlooked in a major floristic treatment.