Quercus engelmannii |
Fagaceae |
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Engelmann oak, Engelmann's oak |
beech family, oak family |
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Habit | Trees, subevergreen, to 10 m. Bark gray or whitish, closely furrowed. | Trees or shrubs, evergreen or deciduous, shrubs sometimes rhizomatous. | ||||||||||||||||
Twigs | light brown, 1-1.5 mm diam., densely or sparsely stellate-tomentose, soon glabrate. |
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Buds | reddish brown, subspheric to broadly ovoid, 1-2 mm, glabrous or basal scales pubescent; stipules persistent about terminal buds. |
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Leaves | blade oblong to elliptic, occasionally lanceolate or ovate, (20-)30-60(-80) × (5-)10-20(-25) mm, base cuneate to cordate, margins entire, undulate, sometimes irregularly toothed, especially toward apex, secondary veins 7-8(-10) on each side, branched, apex acute or broadly rounded; surfaces abaxially blue-green or pale green, densely and loosely glandular-tomentose, quickly glabrate or persistently floccose, especially about base of midrib, at maturity strongly glaucous, adaxially gray-green or pale green, bluish green or glaucous. |
blade lobed or unlobed, pinnately veined, margins serrate, dentate, or entire; surfaces usually pubescent, at least when young, sometimes with scales. |
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Inflorescences | unisexual or androgynous catkins; staminate and androgynous catkins spicate or capitate, rigid, flexible, or lax, consisting of few- to many-flowered clusters, bracts present or absent; pistillate catkins rigid or flexible, with 1-several spicately arranged, rarely solitary, terminal cupules bearing 1-3(-15 or more) pistillate flowers. |
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Staminate flowers | bracteate, bracts often caducous; sepals (3-)4-6(-8); stamens (3-)6-12(-18 or more); petals absent; anthers 2-locular, dehiscing by longitudinal slits, pollen sacs contiguous; pistillode often present and indurate, or vestigial as central tuft of trichomes. |
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Pistillate flowers | calyx of 4-6 distinct or connate sepals; petals absent; pistil 1, 3(-6 or more)-carpellate; ovary inferior, locules as many as carpels; placentation axile; ovules pendulous, 2 in each locule, all but 1 in each pistil usually aborting; styles as many as carpels, distinct to base; stigmas dry; staminodes present or absent. |
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Fruits | nuts, sometimes winged, 1-seeded, subtended or enclosed individually or in groups of 2-3(-15) by scaly or spiny, multibracteate cupule; seed coat membranous; endosperm none; embryo straight, as long as seed; cotyledons fleshy, starchy or oily. |
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Acorns | solitary or paired, subsessile or on peduncle to 5-6 mm; cup cup-shaped or shallowly cup-shaped, 8-10 mm deep × 10-15 mm wide, enclosing 1/3 nut, scales 1.5-3 mm wide, strongly and regularly tuberculate near base of cup, gray-pubescent; nut light brown, ovoid or oblong, 15-25 × 12-14 mm, glabrate or puberulent about apex. |
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Cotyledons | connate. |
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Winter | buds sessile, with few to many imbricate scales (2 valvate scales enclosing imbricate scales in Castanea); terminal bud present or absent. |
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2n | = 24. |
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Quercus engelmannii |
Fagaceae |
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Phenology | Flowering in spring. | |||||||||||||||||
Habitat | Oak woodlands, margins of chaparral, arroyos, slopes and bajadas | |||||||||||||||||
Elevation | 50-1200 m (200-3900 ft) | |||||||||||||||||
Distribution |
CA; Mexico (Baja California)
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Widespread; often dominant forest trees in temperate; subtropical; and tropical areas; mostly Northern Hemisphere |
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Discussion | Quercus engelmannii is closely related to and possibly conspecific with Q. oblongifolia. The cups of Q. engelmannii are larger, deeper, and generally more tuberculate than those of Q. oblongifolia, and the scales are usually larger. Based on available samples, the nuts of Q. engelmannii are consistently larger than those of Q. oblongifolia, apparently with little, if any, overlap in diameter. Considerably more variation occurs within Q. engelmannii in leaf form, possibly reflecting introgression from other white oak species such as Q. cornelius-mulleri, Q. dumosa, and Q. durata (see treatment). On Catalina Island, Quercus engelmannii is known only from a small grove of trees. Putative hybrids between Q. engelmannii and Q. cornelius-mulleri are common in areas of contact between the two species in Riverside and San Diego counties in southern California. Such a population was the basis for Q. acutidens Torrey [Q. dumosa var. acutidens (Torrey) Wenzig]. Other names applied to those populations are Q. macdonaldii var. elegantula Greene and Q. dumosa var. elegantula (Greene) Jepson. Variable in leaf form and stature, those intermediates form extensive populations and are probably best disposed of under the name Q. ×acutidens. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Genera 9, species probably 600-800 (5 genera, 97 species, and numerous hybrids in the flora). In the Western Hemisphere, Fagaceae are found from southern Canada to Colombia; they are absent or infrequent in most of the northern Great Plains and northern Rocky Mountain region. Fagaceae are one of the most important families of Northern Hemisphere woody plants in terms of total biomass and economic use. They are widely used for lumber, firewood, and horticultural plantings; the nuts are often used for animal fodder and, in some species, for human food (particularly Castanea). As dominants in forests, woodlands, and chaparral, native stands of fagaceous trees and shrubs provide optimal wildlife habitat, often harboring an exceptionally diverse insect fauna. Most of the diversity of the family in the Western Hemisphere is concentrated in the genus Quercus, with the greatest number of species in Mexico (at least 125 species), and a secondary area of diversity in the southeastern United States. Polyploidy has not been reported in any natural populations of species of Fagaceae. Natural interspecific hybridization is common in the family, particularly in Quercus, and also in Castanea and Lithocarpus. The most important diagnostic feature of Fagaceae is the cupule, which occurs as the cup or cap of the acorn in Quercus and Lithocarpus and the spiny bur that surrounds the fruits of Castanea and Chrysolepis. The cupule is sometimes referred to as an involuc involucre, however, is made up of bracts, while the cupule has been shown to be a complex structure that is interpreted as an indurated, condensed, partial inflorescence formed by fusion of stem axes with several orders of branching, bearing bracts that are modified as scales and/or spines (see B. S. Fey and P. K. Endress 1983). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 3. | FNA vol. 3, p. 436. | ||||||||||||||||
Parent taxa | Fagaceae > Quercus > sect. Quercus | |||||||||||||||||
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Name authority | Greene: Ill. W. Amer. Oaks 1: 33, plate 17. (1889) | Dumortier | ||||||||||||||||
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