Habit and leaf form. Trees, or shrubs. Plants non-succulent. Leptocaul. Mesophytic. Leaves deciduous; alternate; spiral to distichous; flat; petiolate; non-sheathing; simple; epulvinate. Lamina entire; pinnately veined; cross-venulate. Leaves stipulate. Stipules intrapetiolar; free of one another; caducous. Lamina margins serrate and dentate; flat. Vegetative buds scaly. Leaves without a persistent basal meristem. Vernation conduplicate. Domatia occurring in the family (from Corylus); manifested as hair tufts.
Leaf anatomy. Lamina dorsiventral. Minor leaf veins without phloem transfer cells (Corylus).
Stem anatomy. Nodes tri-lacunar. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. The secondary phloem stratified into hard (fibrous) and soft (parenchymatous) zones. ‘Included’ phloem absent. Xylem with fibre tracheids, or without fibre tracheids; with vessels. Vessels without vestured pits. Wood ring porous; parenchyma rather sparse apotracheal. Sieve-tube plastids S-type.
Reproductive type, pollination. Fertile flowers functionally male, or functionally female. Plants monoecious. Pollination anemophilous.
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in catkins (the male catkins long and pendulous, the females short and erect). The ultimate inflorescence unit racemose (i.e. the male flower solitary in the bract axil, though supposed to represent the central member of a former cymule), or cymose (the paired female flowers representing cymules with the central flower missing). Flowers bracteate; bracteolate (the bracteoles united with the bract); small.
Perianth absent (male flowers), or sepaline (female flowers); 1 whorled.
Androecium 4–8 (each member split almost to the base). Androecial members branched (or split); borne on the bract. Androecium exclusively of fertile stamens. Stamens 4–8. Anthers dehiscing via longitudinal slits; bilocular (the locules separated); tetrasporangiate. Microsporogenesis simultaneous. Tapetum glandular. Pollen grains aperturate; 3 aperturate; porate; 2-celled.
Gynoecium 2 carpelled. The pistil 2 celled. Gynoecium syncarpous; synovarious, or synstylovarious; inferior. Ovary 2 locular. Gynoecium median. Epigynous disk absent. Gynoecium stylate. Styles 2; free; apical. Stigmas dry type; non-papillate; Group II type. Placentation axile to apical. Ovules 1 per locule; funicled; pendulous; anatropous; unitegmic; crassinucellate. Embryo-sac development Polygonum-type. Endosperm formation nuclear.
Fruit non-fleshy; indehiscent; a nut (samaroid, shed with the accrescent involucre of bract plus bracteoles); 1 seeded. Seeds non-endospermic. Embryo well differentiated. Cotyledons 2. Embryo achlorophyllous (1/1); straight. Micropyle not zigzag.
Seedling. Germination cryptocotylar.
Physiology, biochemistry. Flavonols present; kaempferol, quercetin, and myricetin. Sugars transported as oligosaccharides + sucrose. C3. C3 physiology recorded directly in Corylus.
Geography, cytology. Holarctic. Temperate. Widespread North temperate.
Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Rosiflorae; Fagales. Cronquist’s Subclass Hamamelidae; Fagales. APG 3 core angiosperms; core eudicot; Superorder Rosanae; fabid; Order Fagales (as a synonym of Betulaceae).
Species 15. Genera 1; Corylus.
Economic uses, etc. Sources of hazelnuts and filberts.
• Technical details: Corylus.
• Corylus avellana (B. Ent.).
• Corylus avellana: Eng. Bot. 1292, 1868.
Kate, like the hazel twig,
Is straight and slender, and as brown in hue
As hazel nuts, and sweeter than the kernels
(‘Taming of the Shrew’, ii., 1)
We’ll gae down by Clouden side,
Through the hazels spreading wide
(Robert Burns, ‘Hark, the Mavis’)
Where the hazel bank is steepest,
Where the shadow falls the deepest,
Where the clustering nuts fall free
(James Hogg, ‘A Boy’s Song’)