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The families of flowering plants

L. Watson and M.J. Dallwitz

Corylaceae Mirbel

~ Betulaceae.

Habit and leaf form. Trees, or shrubs; 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. Leaf development not ‘graminaceous’. Vernation conduplicate. Domatia occurring in the family (recorded in Corylus); manifested as hair tufts.

Leaf anatomy. The leaf lamina dorsiventral. Mucilaginous epidermis present, or absent. Stomata mainly confined to one surface (abaxial); anomocytic. Hairs present; eglandular and glandular (the former unicellular and uniseriate, striated; the latter clavate). Complex hairs absent. The mesophyll probably containing mucilage cells. Minor leaf veins without phloem transfer cells (Corylus).

Axial (stem, wood) anatomy. Cork cambium present; initially superficial. Nodes tri-lacunar. Primary vascular tissues in a cylinder, without separate bundles; collateral. Internal phloem absent. Cortical bundles absent. Medullary bundles absent. Secondary thickening developing from a conventional cambial ring. Primary medullary rays narrow.

The wood ring porous to semi-ring porous, or diffuse porous (?). The vessels small (sometimes very small). The vessel end-walls scalariform, or scalariform and simple (but then predominantly scalariform). The vessels without vestured pits. The axial xylem with fibre tracheids, or without fibre tracheids; with libriform fibres, or without libriform fibres (the fibre pits rather few, with very small borders); including septate fibres. The fibres without spiral thickening. The parenchyma rather sparse apotracheal. The secondary phloem stratified into hard (fibrous) and soft (parenchymatous) zones. ‘Included’ phloem absent. The wood not storied.

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 units 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, phytochemistry. C3. C3 physiology recorded directly in Corylus. Sugars transported as oligosaccharides + sucrose. Flavonols present; kaempferol, quercetin, and myricetin. Sieve-tube plastids S-type.

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.

General remarks. Readily distinguishable from Betulaceae (q.v.) by the branched androecial members and inferior ovary, but otherwise apparently differing clearly only in the stratified secondary phloem.

Economic uses, etc. Sources of hazelnuts and filberts.


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’)

Illustrations. • Technical details: Corylus. • Corylus avellana (B. Ent., 1831). • Corylus avellana: Eng. Bot. 1292, 1868.

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 13th March 2017.’.