Editing Hazel (section)

==Species==
''Corylus'' has around 14–18 species. The circumscription of species in [[eastern Asia]] is disputed, with [[World Flora Online]] <!-- replaced ''WCSP''--> and the ''Flora of China'' differing in which taxa are accepted, within this region. WFO accepts 17 species while Flora of China accepts 20 species (including ''Corylus mandshurica'').

Only those taxa accepted by both sources are listed below.<ref name="WorldFloraOnline">{{cite web |title=''Corylus'' L. |url=https://www.worldfloraonline.org/taxon/wfo-4000009390 |access-date=19 October 2023}}</ref><ref name=foc>{{cite web |title=''Corylus'' in Flora of China @ efloras.org |url=http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=108088 |website=www.efloras.org |access-date=19 October 2023}}</ref><ref name=fna>Flora of North America: [http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=108088 ''Corylus'']</ref>

The species are grouped as follows:
* Nut surrounded by a soft, leafy [[Involucral bract|involucre]], multiple-stemmed, suckering [[shrub]]s to 12 m tall
** Involucre short, about the same length as the nut
*** ''[[Corylus americana]]'' – American hazel, eastern [[North America]]
*** ''[[Corylus avellana]]'' – Common hazel, [[Europe]] and [[western Asia]]
*** ''[[Corylus heterophylla]]'' – Asian hazel, [[Asia]]
*** ''[[Corylus yunnanensis]]'' – Yunnan hazel, central and southern [[China]]
** Involucre long, twice the length of the nut or more, forming a 'beak'
*** ''[[Corylus colchica]]'' – Colchican filbert, [[Caucasus]]
*** ''[[Corylus cornuta]]'' – Beaked hazel, North America
*** ''[[Corylus maxima]]'' – Filbert, [[southeastern Europe]] and [[southwest Asia]]
*** ''[[Corylus sieboldiana]]'' – Asian beaked hazel, [[northeastern Asia]] and [[Japan]] (syn. ''C. mandshurica'')
* Nut surrounded by a stiff, spiny involucre, single-stemmed [[tree]]s to 20–35 m tall
** Involucre moderately spiny and also with glandular hairs
*** ''[[Corylus chinensis]]'' – Chinese hazel, western China
*** ''[[Corylus colurna]]'' – Turkish hazel, southeastern Europe and [[Asia Minor]]
*** ''[[Corylus fargesii]]'' – Farges' hazel, western China
*** ''[[Corylus jacquemontii]]'' – Jacquemont's hazel, [[Himalaya]]
*** ''[[Corylus wangii]]'' – Wang's hazel, [[southwest China]]
** Involucre densely spiny, resembling a chestnut burr
*** ''[[Corylus ferox]]'' – Himalayan hazel, Himalaya, [[Tibet]] and southwest China (syn. ''C. tibetica'').

Several [[Hybrid (biology)|hybrids]] exist, and they can occur between species in different sections of the genus, e.g. ''[[Corylus × colurnoides]]'' (''C. avellana'' × ''C. colurna'').  The oldest confirmed hazel species is ''[[Corylus johnsonii]]'' found as [[fossil]]s in the [[Ypresian]]-age rocks of [[Ferry County, Washington]].<ref name=Pigg2003>{{cite journal |last1=Pigg |first1=K.B. |author2=Manchester S.R. |author3=Wehr W.C. |year=2003 |title=''Corylus'', ''Carpinus'', and ''Palaeocarpinus'' (Betulaceae) from the Middle Eocene Klondike Mountain and Allenby Formations of Northwestern North America |journal= International Journal of Plant Sciences |volume=164 |issue= 5 |pages=807–822 |doi=10.1086/376816|s2cid=19802370 }}</ref>

Chilean hazel (''[[Gevuina avellana]]''), despite its name, is not related to this genus.<ref>{{cite book |last1=Crawford |first1=Martin |title=Shrubs for Gardens, Agroforestry and Permaculture |date=2020 |publisher=Permanent Publications |isbn=978-1-85623-342-2 |language=en}}</ref>