Abstract
Hazelnuts (Corylus L.) are the source of one of the globally most important nut crops. Despite their economic and cultural importance, taxonomic knowledge is poor, even the number of species is equivocal. Weak morphological differentiation, the inconsistent taxonomic treatment of horticultural selections and cultivars, and uncritical regional treatments generated a multitude of names. The situation is further complicated by an ancient history of use (at least 10 400 years), trade (at least 4000 years) and domestication (at least 2000 years). Here, we present an annotated checklist of the taxa in the genus Corylus based on an extensive literature review, electronic database research, and visits to some European herbaria. Full citations are given for all names, typifications are provided for the majority of them. Cultivars are listed if described under the rules of the ICN. We designate lectotypes and neotypes for 28 names, and discuss the identity of enigmatic C. maxima Mill., a taxon not known from the wild.
Highlights
Species of the genus Corylus L. (Betulaceae Gray) are distributed in the Northern Hemisphere and grow as shrubs or trees
Human use of hazelnuts has an ancient history across its distribution range, and dates back at least to 8400 years BC in western and central Europe (Holst 2010; Zohary et al 2012; Antolín & Jacomet 2015), North America (Abrams & Nowacki 2008; Fine et al 2013) and China (Keightley 1983; Liu & Chen 2012)
Sixty-one of these were described by a single author, Henriksson (1915, 1918, 1923, 1927, 1930, 1931), who meticulously described all differences he found in Scandinavian collections of C. avellana
Summary
Species of the genus Corylus L. (Betulaceae Gray) are distributed in the Northern Hemisphere and grow as shrubs or trees. The detailed morphology of the involucre, the shape and size of the nut, and the leaf indument are the most important morphological traits in species delimitation. Human use of hazelnuts has an ancient history across its distribution range, and dates back at least to 8400 years BC in western and central Europe (Holst 2010; Zohary et al 2012; Antolín & Jacomet 2015), North America (Abrams & Nowacki 2008; Fine et al 2013) and China (Keightley 1983; Liu & Chen 2012). Hazelnuts are one of the most important nut crops world-wide with more than 850 000 tons produced in 2013 (FAOstat 2013), with
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