榛属属

榛属共有十四至十八个物种：

硬果四周有柔软、阔叶的蒴苞，多梗，根孽生，可达12米高。

蒴苞短，跟硬果一样长。

• Corylus americana—美洲榛，美洲东北部；
• Corylus avellana—欧榛，欧洲和西亚；
• Corylus heterophylla—榛，亚洲；
• Corylus yunnanensis—滇榛，中国中、南部；

蒴苞长，比硬果长一倍或更多，形成“长嘴”。

Corylus colchica—Colchican Filbert. 高加索地区；

• Corylus cornuta—长啄榛，北美；
• Corylus maxima—Filbert. 欧洲东南部和亚洲西南部；
• 紫叶榛；
• 地中海榛；
• 伦巴第榛；

Corylus sieboldiana—亚洲长啄榛，亚洲东北部，满洲和日本。

硬果四周有硬挺、多刺的蒴苞，单梗，高达20至35米。

蒴苞带疏刺，并有腺毛。

• Corylus chinensis—华榛，中国西部；
• Corylus colurna—土耳其榛，欧洲东南部和近东；
• Corylus fargesii—披针叶榛. 中国西部；

Corylus jacquemontii—Jacquemont's Hazel. 喜马拉雅山脉；

Corylus wangii—维西榛，中国东南部；

蒴苞带密刺，类似栗子毛刺。

Corylus ferox—藏榛. 西藏地区及中国东南部。

Hazels are plants of the genus Corylus of deciduous trees and large shrubs native to the temperate Northern Hemisphere. The genus is usually placed in the birch family, Betulaceae, though some botanists split the hazels (with the hornbeams and allied genera) into a separate family Corylaceae. The fruit of the hazel is the hazelnut; the trees are also grown as ornaments in hedges or gardens.

Botany

Hazels have simple, rounded leaves with double-serrate margins; young leaves have fine red stipules that are shed at a later age.

The flowers are produced very early in spring before the leaves, and are monoecious, with single-sex catkins. The male catkins are pale yellow and 5–12 centimetres (2–4+3⁄4 inches) long; catkins of the common C. avellana contain 150–200 flowers each collectively producing pollen with a volume as high as 4933 grains/square metre. The female ones are very small and largely concealed in the buds, with only the bright-red, 1-to-3 mm-long styles visible. Hazel pollen, which are often the cause for allergies in late winter or early spring, can be identified under magnification (600×) by their characteristic granular exines bearing three conspicuous pores.

Species

Corylus has around 14–18 species. The circumscription of species in eastern Asia is disputed, with World Flora Online 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.

The species are grouped as follows:

Nut surrounded by a soft, leafy involucre, multiple-stemmed, suckering shrubs 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

Ecology

At least 21 species of fungus have a mutualistic relationship with hazel. Lactarius pyrogalus grows almost exclusively on hazel, and hazel is one of two kinds of host for the rare Hypocreopsis rhododendri. Several rare species of Graphidion lichen depend on hazel trees. In the UK, five species of moth are specialised to feed on hazel including Parornix devoniella. Animals which eat hazelnuts include red deer, dormouse and red squirrel.

Myzocallis coryli, a European species of aphid uses this genus exclusively as its host plant, and has caused major agricultural damage in Oregon to Hazel farms after its introduction to the United States.

Uses

Hazels have many uses and for this reason have been called the "Swiss Army knife of plants".

The nuts of all hazels are edible. The common hazel is the species most extensively grown for its nuts, followed in importance by the filbert. Nuts are also harvested from the other species, but apart from the filbert, none is of significant commercial importance.

A number of cultivars of the common hazel and filbert are grown as ornamental plants in gardens, including forms with contorted stems (C. avellana 'Contorta', popularly known as "Corkscrew hazel" or "Harry Lauder's walking stick" from its gnarled appearance); with weeping branches (C. avellana 'Pendula'); and with purple leaves (C. maxima 'Purpurea').

Hazel is a traditional material used for making wattle, withy fencing, beanpoles, baskets, and the frames of coracle boats.

Culture

The Celts believed hazelnuts gave one wisdom and inspiration. There are numerous variations on an ancient tale that nine hazel trees grew around a sacred pool, dropping into the water nuts that were eaten by salmon (a fish sacred to Druids), which absorbed the wisdom. A Druid teacher, in his bid to become omniscient, caught one of these special salmon and asked a student to cook the fish, but not to eat it. While he was cooking it, a blister formed and the pupil used his thumb to burst it, which he naturally sucked to cool, thereby absorbing the fish's wisdom. This boy was called Fionn Mac Cumhail (Fin McCool) and went on to become one of the most heroic leaders in Gaelic mythology.

"The Hazel Branch" from Grimms' Fairy Tales claims that hazel branches offer the greatest protection from snakes and other things that creep on the earth.