Quercus engelmannii |
Quercus chihuahuensis |
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Engelmann oak, Engelmann's oak |
Chihuahua oak, Chihuahuan oak, felt oak |
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Habit | Trees, subevergreen, to 10 m. Bark gray or whitish, closely furrowed. | Shrubs or trees, deciduous, to 10 m. Bark gray, furrowed, checkered, or scaly. |
Twigs | light brown, 1-1.5 mm diam., densely or sparsely stellate-tomentose, soon glabrate. |
gray, 2-3(-4) mm diam., densely tomentose. |
Buds | reddish brown, subspheric to broadly ovoid, 1-2 mm, glabrous or basal scales pubescent; stipules persistent about terminal buds. |
reddish brown, broadly ovoid, distally rounded, 2-2.5 mm, densely yellowish pubescent; scales gray-puberulent; stipules persistent, 1-4, subulate, pubescent, at base of terminal buds. |
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 elliptic or oblong to ovate or obovate, (25-)40-50(-85) × (18-)20-30(-50) mm, base rounded or shallowly cordate, margins entire or toothed to sublobate, secondary veins 8 to 10 on each side, somewhat branching, apex broadly rounded to acute; surfaces abaxially yellowish or grayish, densely stellate with velvety hairs, adaxially green, sparsely soft-pubescent with prominent, spreading, stellate hairs, felty to touch, secondary veins somewhat prominent on both surfaces, even under dense tomentum. |
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. |
1-3 on tomentose peduncle 15-35(-60) mm; cup hemispheric, 7-10 mm deep × 10-15 mm wide, enclosing 1/2 nut, scales proximally thickened, distally appressed, densely gray-puberulent, tips reddish, ultimately glabrate; nut ovoid, 14-18 × 10-12 mm, puberulent, eventually glabrate. |
Cotyledons | connate. |
connate. |
2n | = 24. |
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Quercus engelmannii |
Quercus chihuahuensis |
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Phenology | Flowering in spring. | Flowering spring. |
Habitat | Oak woodlands, margins of chaparral, arroyos, slopes and bajadas | Oak and pinyon-juniper woodlands, grassy hills, sometimes extending into dry thorn scrub and bursera woodland (Mexico) |
Elevation | 50-1200 m (200-3900 ft) | 400-2000 m (1300-6600 ft) |
Distribution |
CA; Mexico (Baja California)
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TX; Mexico (Chihuahua, Sonora, Zacatecas, and San Luis Potosí)
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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.) |
Quercus chihuahuensis is a distinctive species throughout its range, mostly in dry montane western Mexico; it occurs in the United States only as putative hybrids with Q. grisea (the Eagle and Quitman mountains) and Q. arizonica (Hueco Tanks) in Texas. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 3. | FNA vol. 3. |
Parent taxa | Fagaceae > Quercus > sect. Quercus | Fagaceae > Quercus > sect. Quercus |
Sibling taxa | ||
Synonyms | Q. infralutea, Q. jaliscensis, Q. santaclarensis | |
Name authority | Greene: Ill. W. Amer. Oaks 1: 33, plate 17. (1889) | Trelease: Mem. Natl. Acad. Sci. 20: 85. (1924) |
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