Flora of North America species comparison

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Quercus pacifica

Quercus prinoides

Channel Island scrub oak, island scrub oak, Pacific oak

dwarf chestnut oak, dwarf Chinkapin oak, dwarf chinquapin oak, scrub chestnut oak
Habit Shrubs, rarely small trees, subevergreen, shrubs to 2 m, trees to 5 m or taller. Shrubs, deciduous, (0.5-)1-3(-5, 10?) m, sometimes spreading-rhizomatous.
Bark

scaly on older branches and trunk.

gray, thin, flaky to papery.
Twigs

brownish or reddish, minutely puberulent, becoming glabrate and gray with age.

brownish, 1.5-3(-4) mm diam., sparsely fine-pubescent, soon becoming glabrate, graying in 2d year.
Buds

light or chestnut brown, ovate or globose, 2-3 × 1-2 mm.

brown to red-brown, subrotund to broadly ovoid, 1-3 mm, apex rounded, very sparsely pubescent.
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 oblanceolate or usually obovate, 40-140 × 20-60(-80) mm, leathery, base truncate to cuneate, margins regularly undulate, toothed or shallow-lobed, teeth usually acute, sometimes rounded, or acute-acuminate, often strongly antrorse, secondary veins usually 5-8(-9) on each side, ± parallel, apex short-acute to acuminate;

surfaces abaxially glaucous or light green, appearing glabrate, with scattered or crowded minute, appressed, symmetric, 6-10-rayed, stellate hairs, adaxially lustrous dark green, glabrate.
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.

solitary or paired, subsessile or on axillary peduncle to 3-8 mm;

cup deeply or shallowly cup-shaped, 9-12 mm deep × 13-17(-22) mm wide, enclosing 1/4-1/3 nut, base rounded, margin usually thin, scales rather tightly appressed, moderately tuberculate, uniformly short gray-pubescent;

nut light brown, oblong to ovoid, (13-)15-20 × 10-13 mm.
Cotyledons

distinct.

distinct.

Quercus pacifica

Quercus prinoides
Phenology Flowering spring. Flowering in spring.
Habitat Chaparral, oak woodlands, margins of grasslands, understory in closed-cone pine stands Pine barrens, scrublands, forest margins, prairies, and exposed ridges, on deep sands or dry shale, rarely reported on calcareous soils
Elevation 0-300 m (0-1000 ft) 0-500 m (0-1600 ft)
Distribution
from FNA
CA
[WildflowerSearch map]
[BONAP county map]
from FNA
AL; AR; CT; GA; IA; IL; IN; KY; MA; MI; MO; NC; NH; NJ; NY; OH; OK; PA; RI; SC; TN; VA; VT; WV; ON
[WildflowerSearch map]
[BONAP county map]
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.)

Some reports of Quercus prinoides growing in calcareous soils are probably referable to shrub forms of Q. muhlenbergii.

The debate over whether Quercus prinoides is distinct from Q. muhlenbergii has continued for most of the last century. Little doubt can exist that strong genetic differences, as expressed by characteristics of habit, leaf form, and habitat preference, separate the two taxa; the question is merely whether they are best treated as subspecies or varieties or as separate species. Over most of the eastern United States, the two taxa occur sympatrically over broad areas with little immediate contact (syntopy), because Q. muhlenbergii is found on calcareous soils and Q. prinoides occurs on sands (often acidic) and dry shales. Seedlings of Q. prinoides can flower and produce acorns in as few as 3-5 years from planting, when only 20-50 cm, and maintain their dwarf, clonal habit in cultivation. Quercus muhlenbergii begins fruiting as a small tree of 3 m or more in height. Because of these differences, and interdigitating geographic distributions, the two taxa seem to be similar in pattern of variation and interaction to other closely related oak species of eastern North America, and dissimilar in pattern to infraspecific taxa such as we see in Q. sinuata var. sinuata and Q. sinuata var. breviloba. The populations that are difficult to determine are usually small scrubby trees, probably mostly Q. muhlenbergii, stunted because of less than favorable moisture conditions, with or without indications of introgression from Q. prinoides.

Material of Quercus prinoides from Long Island, coastal Massachusetts, Nantucket Island, and Martha's Vineyard has been segregated as Q. prinoides Willdenow var. rufescens Rehder on the basis of vestiture and minor differences in leaf form. These populations have appressed-stellate leaf pubescence abaxially, as throughout the range of the species; in addition they have reddish, erect, fasiculate hairs similar to those found in Q. michauxii. The hairs make the abaxial leaf surface somewhat felty to the touch. Variability in this characteristic and lack of other consistently correlated features preclude taxonomic recognition of Q. prinoides var. rufescens, but this problem is worthy of further investigation.

(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
Q. acerifolia, Q. agrifolia, Q. ajoensis, Q. alba, Q. arizonica, Q. arkansana, Q. austrina, Q. berberidifolia, Q. bicolor, Q. boyntonii, Q. buckleyi, Q. carmenensis, Q. chapmanii, Q. chihuahuensis, Q. chrysolepis, Q. coccinea, Q. cornelius-mulleri, Q. depressipes, Q. douglasii, Q. dumosa, Q. durata, Q. ellipsoidalis, Q. emoryi, Q. engelmannii, Q. falcata, Q. fusiformis, Q. gambelii, Q. garryana, Q. geminata, Q. georgiana, Q. graciliformis, Q. gravesii, Q. grisea, Q. havardii, Q. hemisphaerica, Q. hinckleyi, Q. hypoleucoides, Q. ilicifolia, Q. imbricaria, Q. incana, Q. inopina, Q. intricata, Q. john-tuckeri, Q. kelloggii, Q. laceyi, Q. laevis, Q. laurifolia, Q. lobata, Q. lyrata, Q. macrocarpa, Q. margarettae, Q. marilandica, Q. michauxii, Q. minima, Q. mohriana, Q. montana, Q. muehlenbergii, Q. myrtifolia, Q. nigra, Q. oblongifolia, Q. oglethorpensis, Q. pagoda, Q. palmeri, Q. palustris, Q. phellos, Q. polymorpha, Q. prinoides, Q. pumila, Q. pungens, Q. robur, Q. robusta, Q. rubra, Q. rugosa, Q. sadleriana, Q. shumardii, Q. similis, Q. sinuata, Q. stellata, Q. tardifolia, Q. texana, Q. tomentella, Q. toumeyi, Q. turbinella, Q. vacciniifolia, Q. vaseyana, Q. velutina, Q. viminea, Q. virginiana, Q. wislizenii
Q. acerifolia, Q. agrifolia, Q. ajoensis, Q. alba, Q. arizonica, Q. arkansana, Q. austrina, Q. berberidifolia, Q. bicolor, Q. boyntonii, Q. buckleyi, Q. carmenensis, Q. chapmanii, Q. chihuahuensis, Q. chrysolepis, Q. coccinea, Q. cornelius-mulleri, Q. depressipes, Q. douglasii, Q. dumosa, Q. durata, Q. ellipsoidalis, Q. emoryi, Q. engelmannii, Q. falcata, Q. fusiformis, Q. gambelii, Q. garryana, Q. geminata, Q. georgiana, Q. graciliformis, Q. gravesii, Q. grisea, Q. havardii, Q. hemisphaerica, Q. hinckleyi, Q. hypoleucoides, Q. ilicifolia, Q. imbricaria, Q. incana, Q. inopina, Q. intricata, Q. john-tuckeri, Q. kelloggii, Q. laceyi, Q. laevis, Q. laurifolia, Q. lobata, Q. lyrata, Q. macrocarpa, Q. margarettae, Q. marilandica, Q. michauxii, Q. minima, Q. mohriana, Q. montana, Q. muehlenbergii, Q. myrtifolia, Q. nigra, Q. oblongifolia, Q. oglethorpensis, Q. pacifica, Q. pagoda, Q. palmeri, Q. palustris, Q. phellos, Q. polymorpha, Q. pumila, Q. pungens, Q. robur, Q. robusta, Q. rubra, Q. rugosa, Q. sadleriana, Q. shumardii, Q. similis, Q. sinuata, Q. stellata, Q. tardifolia, Q. texana, Q. tomentella, Q. toumeyi, Q. turbinella, Q. vacciniifolia, Q. vaseyana, Q. velutina, Q. viminea, Q. virginiana, Q. wislizenii
Synonyms Q. dumosa var. polycarpa Q. prinoides var. rufescens
Name authority Nixon & C. H. Muller: Novon 4: 391. (1994) Willdenow: in G. H. E. Muhlenberg, Ges. Naturf. Freunde Berlin Neue Schriften 3: 397. (1801)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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