Quercus pacifica |
Quercus graciliformis |
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Channel Island scrub oak, island scrub oak, Pacific oak |
Chisos oak |
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Habit | Shrubs, rarely small trees, subevergreen, shrubs to 2 m, trees to 5 m or taller. | Trees, tardily deciduous, to 8 m. Bark gray, furrowed. |
Bark | scaly on older branches and trunk. |
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Twigs | brownish or reddish, minutely puberulent, becoming glabrate and gray with age. |
straw colored to brown or deep reddish brown, 1-2 mm diam., glabrate or somewhat pubescent at apex. |
Buds | light or chestnut brown, ovate or globose, 2-3 × 1-2 mm. |
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Leaves | blade obovate or oblong, planar to moderately convex or undulate, 15-40 × 7-20(-40) mm, base cuneate or rounded, attenuate-decurrent along petiole, margins minutely cartilaginous, entire or with 1-5 irregular teeth on each side, secondary veins obscure, 1-5 on each side, apex blunt or rounded, occasionally subacute with mucronate tip; surfaces abaxially waxy, glandular, with scattered minute, flat, appressed, ± 8-rayed stellate hairs, not obscuring surface, adaxially green, glossy, glabrate or with minute, scattered, stellate hairs. |
blade lanceolate to narrowly elliptic, widest proximal to middle, 45-90 × 10-25 mm, base rounded to cuneate, margins entire or with 8-10 teeth or shallow lobes with rounded sinuses, awns 1-9, apex acute to long-attenuate; surfaces abaxially glabrous or occasionally with small axillary tufts of tomentum, adaxially glabrous except for scattered pubescence near base and along midrib. |
Acorns | paired or solitary in leaf axil, subsessile, rarely pedunculate in teratological forms; cup hemispheric to turbinate, to 15 mm deep × 20 mm wide, enclosing only 1/4-1/2 nut, scales moderately to heavily tuberculate, irregularly formed; nut light brown, acute-cylindric or fusiform, tapered, (15-)20-30 × (6-)9-15 m, apex acute, glabrate. |
biennial; cup saucer- to shallowly bowl-shaped, 4-6 mm high × 7-10 mm wide, covering 1/4-1/3 nut, outer surface puberulent to glabrate, inner surface uniformly pubescent, scales appressed, acute, occasionally tuberculate at base; nut ovoid to narrowly ellipsoid, 9-18 × 7-10 mm, minutely puberulent, scar diam. 3-4.5 mm. |
Cotyledons | distinct. |
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Terminal | buds glossy brown or red-brown, ovoid, 1.5-3 mm, minutely ciliate. |
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Quercus pacifica |
Quercus graciliformis |
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Phenology | Flowering spring. | Flowering spring. |
Habitat | Chaparral, oak woodlands, margins of grasslands, understory in closed-cone pine stands | Dry rocky canyons of the Chisos Mountains |
Elevation | 0-300 m (0-1000 ft) | 0-1650 m (0-5400 ft) |
Distribution |
CA
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TX |
Discussion | Of conservation concern. Quercus pacifica is endemic on three of the California Channel Islands: Santa Cruz, Santa Catalina, and Santa Rosa. It is not known from the mainland, but it bears a superficial similarity to some of the tree forms that are putative hybrids between Q. engelmannii and Q. cornelius-mulleri in San Diego County. The latter populations, sometimes treated as Q. ×acutidens, differ in having much greater variability in leaf shape; thicker, more leathery leaves; denser abaxial leaf vestiture; much smaller hairs, having more than 10 rays; and variable levels of connation of cotyledons (always distinct in Q. pacifica). Quercus pacifica appears to be most closely related to Q. douglasii, whether by direct descent or by introgression with another species no longer extant on the islands. Quercus ×macdonaldii Greene (as a species) [= Quercus dumosa var. macdonaldii (Greene) Jepson] is a stabilized hybrid complex between Quercus pacifica and Q. lobata Née. The plants tend to be small to moderate trees with leaves that resemble those of Q. lobata; the leaves are much more shallowly lobed and always less than two-thirds the distance from the margin to the midrib. Quercus ×macdonaldii is known from Santa Rosa, Santa Cruz, and Santa Catalina islands. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Of conservation concern. Quercus graciliformis reportedly hybridizes with Q. emoryi. (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. Lobatae |
Sibling taxa | ||
Synonyms | Q. dumosa var. polycarpa | Q. canbyi, Q. graciliformis var. parvilobata |
Name authority | Nixon & C. H. Muller: Novon 4: 391. (1994) | C. H. Muller: Torreya 34: 120. (1934) |
Web links |