Oaks of the World

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Botanical characters

Fagaceae - Cyclobalanopsis - Quercus

Genus : Quercus L.
Family : Fagaceae Dumortier
Order : Fagales

Trees or shrubs, deciduous or evergreen; monoecious.
Stipules early deciduous. Leaves alternate, simple, spirally arranged.
Inflorescences : unisexual or androgynous catkins (in genus Quercus, inflorescences are always unisexual). Male and androgynous catkins spicate, consisting of few- to many-flowered clusters; pistillate catkins spicate, with one to several cupules bearing the pistillate flowers.
Male flowers with bracts often deciduous; 4-6(9) sepals ; 6-12 or more stamens; petals absent; pistillode often present.
Female flowers with 4-6 sepals, no petals, 1 pistil, 3 or more carpels, ovary inferior, styles and locules as many as carpels, placentation axile, 2 pendulous ovules in each locule, all but 1 aborting; staminodes sometimes present.
Fruits : nuts 1-seeded, enclosed by multibracteate cupule; no endosperm; embryo as long as seed.
Genera 8-9 : Castanea, Castanopsis, Chrysolepis, Colombobalanus, Fagus, Formanodendron, Lithocarpus, Quercus (divided into 2 sub-genera : Cyclobalanopsis and Quercus), Trigonobalanus. Genus Nothofagus has recently been placed in a new monotypic Family : Nothofagaceae Kuprianova.
The main feature of Fagaceae is the cupule : it is the cup of the acorn in Quercus and Lithocarpus, and the spiny bur surrounding fruits of Castanea and Chrysolepis.
600 - 900 species; widespread, forming forest trees in temperate to sub-tropical areas of Northern Hemisphere. Interspecific hybridization is common, particularly in Quercus.

Genus Quercus L. 1753

1/ Quercus L. sub-genus Cyclobalanopsis (Oersted) C.K. Schneider
(= Genus Cyclobalanopsis Oersted 1867)

Trees, rarely shrubs, evergreen; monoecious.
Bark usually smooth, rarely furrowed.
Buds ovoid (more or less globose, or conical or ellipsoid), with numerous imbricated scales.
Stipule extrapetiolar.
Leaves spirally arranged.
Male flowers
drooping, more or less clustered into racemes; perianth with 5-6 pieces, stamens as many as perianth pieces, sometimes less; styles slender; pistil rudimentary.
Female flowers
solitary, perianth with 5-6 pieces, staminodes sometimes present and small; ovary with 3 locules ; (2)3(4) styles ;
: acorn, more or less enclosed in the cupule;
solitary; scales whorled, connate, in concentric rings.
: 1 in each cupule, the aborted ovule persistent besides.
Hypogeal germination.
150 species, mainly in tropical and subtropical Asia; 43 endemic species in China (where they occur essentially in South, while Quercus occur in North).
2/ Quercus L. sub-genus Quercus

Quercus is a very important (perhaps the most) woody genus in the Northern Hemisphere.
Trees or shrubs, evergreen or deciduous; monoecious;
Twigs tomentose when young, with simple or stellate hairs, then glabrescent, brownish;
Terminal buds ovoid-conical or ovoid-globose, rarely ovoid-ellipsoid, with imbricate scales, densely covered with yellow pubescence;
Leaves alternate, lobed or unlobed, thin or leathery, margin entire or toothed, or spiny; spirally arranged; secondary veins more or less parallel and extending to margin, or branched and anastomosing before reaching margin; midrib and lateral veins abaxially very prominent; leaf blade glabrous or pubescent, with simple or stellate hairs, pubescence mainly beneath; stipules extrapetiolar, straight and pointed, deciduous and inconspicuous (except in Q.sadleriana).
Male inflorescences on catkins in axils of leaves, usually clustered at the base of a new growth, lax, spicate, with straight, pointed, deciduous and tomentose bracts; staminate flowers with sepals connate, (4)-6-(9) stamens, style slender, anthers 0.5-1 mm long; pistillode usually absent ;
Pistillate inflorescences usually stiff, at axil of apical leaves, erect, pubescent, with terminal cupule and 1-several lateral ones; bracts straight, pointed, pubescent, deciduous ; pistillate flower : 1 in each cupule; perianth with (4)-6-(9) connate pieces; 3-(6) carpels and styles; stigmas glabrous;
Fruit : acorn, in cup covering base of nut or more (rarely whole nut); ovoid conical, sometimes globose, apically rounded or sometimes depressed, mucronate or not. Maturing in 1 or 2 years. x = 12. Hypogeal germination.
Cupule saucer-, cup- or bowl-shaped, stalked or sessile, covered with scales imbricate or tuberculate, appressed or weakly reflexed;
Species ca. 400 : North America, Mexico, West Indies, Central America, South America (Colombia only), Africa and Eurasia.