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Island Oak
Quercus tomentella
About Island Oak (Quercus tomentella) Nurseries Show All Photos The Island Oak (Quercus tomentella), also known as Island Live Oak or Channel Islands Oak, is an oak in the section Protobalanus. It is a rare species, included on CNPS list 4.2 due to limited distribution in the wild. Fossil evidence shows that this species was once widespread on the mainland. Island Oak is endemic to six islands off the coast of California, Santa Rosa, Santa Cruz, Anacapa, Santa Catalina, San Clemente, and Guadalupe islands. The first five islands are Channel Islands of California; Guadalupe Island is located to the west of Baja California, Mexico. Island Oak is a tree usually less than 20 meters in height. Its bark is usually gray and becomes furrowed with age. The specific name tomentella, Latin for "beset with tomentum (fuzz)", references the dense hairs found on the undersides of its leaves. Leaves, which are evergreen, are usually 5-8 centimeter in length, oblong to oblong-obvate in shape, with a toothed margin, deeply indented. Acorns take 2 years to mature and are saucer- to bowl-shaped with a rounded tip, and large in size (cup 20-30 millimeter wide, 6-8 millimeter deep, nut 20-35 millimeter).

In the garden it is fast growing and trouble-free. It is best used near the coast, but can tolerate inland conditions within about 20 miles of the coast if given some protection and a little extra water during dry times, especially when the young plant is getting established.
Plant Description
Plant Type

Max. Height
33 - 66 ft (10.1 - 20.1 m)

Max. Width
35 ft (10.7 m)

Rounded, Upright Columnar

Growth Rate
Fast, Moderate


Flower Color
Cream, Green

Flowering Season
Spring, Summer

Native Status
Natural Setting
Site Type
Slopes, bluffs and canyons of the Channel Islands where fog is frequent

Sun, Part Shade

Elevation ?
-2006' - 2362'

Annual Precip. ?
7.8" - 19.5"

Summer Precip. ?
0.14" - 0.40"

Coldest Month ?
45.6° F - 57.6° F

Hottest Month ?
62.9° F - 73.3° F

Humidity ?
1.50 vpd - 16.69 vpd

Soil Description
Tolerates a wide variety of soils, including very rocky conditions

Soil PH
6.0 - 7.2


Cold Tolerance(° F)
Tolerates cold to 15° F

Sunset Zones ?
5, 7, 8, 9, 14*, 15*, 16*, 17*, 19*, 20*, 21*, 22*, 23*, 24*

Companion Plants
Due to its relative large leaves and dense foliage, it often has no understory. However, it can be used adjacent to many other island plants such as Santa Cruz Island Ironwood (Lyonothamnus floribundus ssp. asplenifolius), Catalina Cherry (Prunus ilicifolia ssp. lyonii), Island Bristleweed (Hazardia detonsa), Redflower Buckwheat (Eriogonum grande var. rubescens), Island Snapdragon (Gambelia speciosa), and Giant Coreopsis (Leptosyne gigantea). Other chaparral and sage scrub companions include California Encelia (Encelia californica), California Sagebrush (Artemisia californica), Bladderpod (Peritoma arborea), and Ceanothus spp

Wildlife Attracted
Many insects, birds, reptiles and mammals are attracted to oaks. Many insects are attracted to Oaks generally, including the following butterflies which use Oaks as host plant: California Sister, Propertius Duskywing, Mournful Duskywing, Golden Hairstreak, and Gold-Hunter's Hairstreak.

Landscaping Information
Ease of Care
Moderately Easy

Water Requirement ?
Extremely Low
Very Low
Moderate - High

Moderately Popular

Max. Summer Water ?
1x/month, 2x/month
No Summer Water
Keep moist

Organic with Rocks

Propagation ?
For propagating by seed: Fresh seeds sow in fall outdoors or stratify to hold for spring sowing. (USDA Forest Service 1974).

Common uses
Bank Stabilization, Hedges, Bird Gardens, Butterfly Gardens

Nursery Availability
Commonly Available

Other Names
Common Names
Island Live Oak

Sources include: Wikipedia. All text shown in the "About" section of these pages is available under the Creative Commons Attribution-ShareAlike License. Plant observation data provided by the participants of the California Consortia of Herbaria, Sunset information provided by Jepson Flora Project. Propogation from seed information provided by the Santa Barbara Botanical Garden from "Seed Propagation of Native California Plants" by Dara E. Emery. Sources of plant photos include CalPhotos, Wikimedia Commons, and independent plant photographers who have agreed to share their images with Calscape. Other general sources of information include Calflora, CNPS Manual of Vegetation Online, Jepson Flora Project, Las Pilitas, Theodore Payne, Tree of Life, The Xerces Society, and information provided by CNPS volunteer editors, with special thanks to Don Rideout. Climate data used in creation of plant range maps is from PRISM Climate Group, Oregon State University, using 30 year (1981-2010) annual "normals" at an 800 meter spatial resolution.

Links:   Jepson eFlora Taxon Page  CalPhotos  Wikipedia  Calflora

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