Species
Corylus has 14–18 species. The circumscription of species in eastern Asia is disputed, with WCSP and the Flora of China differing in which taxa are accepted; within this region, only those taxa accepted by both sources are listed below. The species are grouped as follows:
- Nut surrounded by a soft, leafy involucre, multiple-stemmed, suckering shrubs to 12m 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)
- Involucre short, about the same length as the nut
- Nut surrounded by a stiff, spiny involucre, single-stemmed trees 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).
- Involucre moderately spiny and also with glandular hairs
Several hybrids exist, and 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 fossils in the Ypresian-age rocks of Ferry County, Washington, USA.
Read more about this topic: Hazel
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