Hazel
Common Hazel (Corylus avellana ), illustration
The hazels (Corylus ) are a genus of woody shrubs and trees in the birch family ( Betulaceae ).
- 6.1 Notes and references
- 6.2 Literature
Description
Vegetative characteristics
Hazel are 3-15 m tall shrubs, but usually single-stemmed trees, which drop their leaves in the winter. They usually branch into a number of branches, without a main trunk train, the trunks and branches are turning around. The grayish brown, thin and smooth bark shows no striking Korkporen, it is closed and breaks the age in vertical stripes and scales. The wood is nearly white to light brown, fine- textured, medium-hard and hard. Branches, twigs and branches are distributed to standing in two rows. The young branches differ in long and short shoots. Before winter the plants form sessile, broadly ovate buds that are pointed upward and possess several smooth, like roof tiles overlapping scales.
The leaves are double row, both on the long and the short shoots. The leaf blade is broadly ovate, base often cordate, the tip occasionally almost lobed, the margins are doubly serrated. The 4 to 12 cm long and 3.5 and 12 cm wide leaf blade is crossed by eight or fewer pair of lateral veins, it is thin, the underside is usually finely hairy and sometimes glandular.
Inflorescences and flowers
The hazels are monoecious bisexual ( monoecious ). The male inflorescences ( catkins ) are on the branches of the short shoots in many grape-like groups. They are formed in the previous year and through the winter naked to kick before the leaves. Within the male catkins the flowers are surrounded threes pushed by a scale-like bract. Form four stamens, which are virtually divided to half, thus forming eight half stamens. The stamens are fused very short and the two continue reading on the carrier sheet.
Above the male catkins are the female inflorescences as smaller groups of flowers and bracts, two female flowers held by a bract. The female flowers bloom at the same time as the male flowers, they are reduced and only the stylus comes out in the heyday of the bud.
Pollen
Pollen from hazel species are often the cause of allergic rhinitis in late winter and early spring. The pollen grains are easily identified by a palynological investigation by the tiporate and rare tetraporate structure of their granular exine.
Fruits
The fruit stands are dense groups, which consist of several fruits. Each fruit is surrounded by an involucre formed by two bracts. The bracts are leaves- leaf-like, hairy or spiny, enlarged and occasionally fused to a short to extended tube. The nut fruits are relatively thin, nearly spherical to ovoid, laterally and longitudinally ribbed they are pressed something.
Occurrence
The species of the genus are in the temperate areas of the northern hemisphere, spread from North America to Europe to Asia.
Ecology
Hazel accommodate 44 species caterpillars.
System
Within the birch family ( Betulaceae ) the genus in the subfamily of hazelnut plants ( Coryloideae ) is classified. Phylogenetic analyzes place the genus as Schwesterklade to the remaining three genera of the family.
Corylus
Carpinus
Ostrya
Cladogram after
Depending on the author between ten and 25 species can be distinguished within the genus Corylus. Current treatments differ in the following ways:
- American hazel (Corylus americana Walter )
- Common Hazel (Corylus avellana L.) Corylus avellana var avellana
- Corylus avellana var pontica ( K.Koch ) HJPWinkl.
- Corylus cornuta subsp. californica ( A.DC. ) A.E.Murray
- Corylus cornuta subsp. cornuta
- Corylus ferox var ferox
- Corylus ferox var tibetica ( Batalin ) Franch.
- Corylus heterophylla var heterophylla
- Corylus heterophylla var sutchuenensis Franch.
- Corylus mandshurica var sieboldiana ( Maxim. ) CKSchneid.
- Corylus sieboldiana var sieboldiana
Depending on the author's opinion are of Corylus avellana Corylus maxima Mill often the species ( Lambert Hazel ), Corylus pontica K.Koch and Corylus colchica Albov split. In addition, depending on the author, the type Corylus californica (A. DC. ) A. Heller is counted as a variety of Corylus cornuta. Similarly, the frequently asked to Corylus heterophylla var sutchuenensis Franch be. and var yunnanensis Franch. out by some authors as distinct species. Also contentious rank has Corylus papyracea.
Fossil evidence
A first fossil evidence of hazel nuts based on that of multi-lobed, foliage leaf -like and spiny bracts are surrounded, dates from the Middle Eocene and was found at Republic in the U.S. state of Washington. Fossil leaves that resemble those of Corylus species are known from the northern hemisphere from many finds from the Paleocene and Eocene. However, a precise assignment to the genus Corylus or Palaeocarpinus is not possible.