The coast live oak (Quercus agrifolia), also called the California live oak, is a live oak (a semi-evergreen oak) native to the California Floristic Province. Live oaks are so-called because they keep living leaves on the tree all year, adding young leaves and shedding dead leaves simultaneously rather than dropping dead leaves en masse in the autumn like a true deciduous tree. The coast live oak may be shrubby, depending on age and growing location, but is generally a medium-sized tree. It grows west of the Sierra Nevada mountain range from Mendocino County, California, south to northern Baja California in Mexico. It is classified in the red oak section of oaks (Quercus sect. Lobatae), subsection Agrifoliae. This species is commonly sympatric with canyon live oak (Q. chrysolepis), and the two may be hard to distinguish because their spinose leaves are superficially similar.
Description Coast live oak typically has a much-branched trunk and reaches a mature height of 10–25 meters (33–82 feet). Some specimens may attain an age exceeding 1,000 years. Examples of this include the Grand Oak of Cherry Valley, California, the Encino Oak Tree, which died in the 1990s (part of the stump has been preserved) and the Pechanga Great Oak. The tree is extremely drought-tolerant.[3]
Trunk and stem The trunk, particularly for older individuals, may be highly contorted, massive and gnarled. The crown is broadly rounded and dense, especially when aged 20 to 70 years; in later life the trunk and branches are more well defined and the leaf density lower. The oldest specimens might exceed 6 m (20 ft) in trunk circumference and 30 m (100 ft) in height. The bark is gray to dark-brown or black colored, with broad ridges and rounded. Twigs are brown to red-brown, measuring 1.5–3 millimeters in diameter, with scattered or uniform pubescence. Terminal buds are light chestnut-brown, oval-shaped, occasionally nearly conical, measuring 3–6 mm, and are glabrous except for cilia along scale margins.
Leaf Leaf petioles measure 4–14 mm, rarely 18 mm, with a sparsely to densely pubescent surface. The dark green leaf blades are broadly oval, often convex in shape, with a rounded or cordate base and a blunt to attenuate apex, measuring 2–7 centimeters (3⁄4–2+3⁄4 inches) long and 1–4 cm (1⁄2–1+1⁄2 in) broad; the leaf margin is spiny-toothed (spinose), with sharp thistly fibers extending from the lateral leaf veins. The leaf surface is glabrous or with small auxiliary tufts of tomentum abaxially and raised veins; the adaxial leaf surface is convex, wrinkled, glabrous, and occasionally densely uniformly pubescent.
The outer layers of leaves are designed for maximum solar absorption, containing two to three layers of photosynthetic cells. These outer leaves are deemed to be small in size to more efficiently re-radiate the heat gained from solar capture. Shaded leaves are generally broader and thinner, having only a single layer of photosynthetic cells. The convex leaf shape may be useful for interior leaves which depend on capturing reflected light scattered in random directions from the outer canopy. The leaf shape may be also useful as condensation surfaces for "dew and mist, which would allow the tree to survive years with limited rainfall".
Flower and fruit The flowers are produced in early-to-mid spring; the male flowers are pendulous catkins 5–10 cm (2–4 in) long, the female flowers inconspicuous, less than 0.5 cm (1⁄4 in) long, with 1–3 clustered together. Flowering occurs in early to mid spring. The fruit is a slender reddish brown acorn 2–3.5 cm (3⁄4–1+1⁄2 in) long and 1–1.5 cm (3⁄8–5⁄8 in) broad, with the basal quarter enclosed in a cupule. The acorn cup is turbinate (beetroot-shaped) to cup or bowl shaped, rarely saucer-shaped, covering a fourth to a third, rarely half, of the nut; the cup is ovoid to oblong or conic, with a glabrous to sparsely puberulent outer surface; the inner surface is pubescent on the innermost third to uniformly pubescent, with acute scales and loose tips. The acorn nut is ovoid to oblong or conic in shape, with a glabrous surface. Unusually for a red oak, the acorns mature about 7–8 months after pollination (most red oak acorns take 18 months to mature).
Taxonomy
Recognized varieties There are two varieties of Quercus agrifolia:
Hybridity Several hybrids between coast live oak and other red oak species have been documented. Hybrids with interior live oak (Q. wislizenii) are known in many areas in northern California. Coast live oak also hybridizes with Shreve oak (Q. parvula var. shrevei). All these oak species show evidence of introgression with one another.
Etymology In naming the species, Née compared it to a species illustrated in Leonard Plukenet's Phytographia under the descriptive name "Ilex folio agrifolii americana, forte agria, vel aquifolia glandifera" which Plukenet had compared, in his Almagestum botanicum, to Luigi Anguillara's Agrifolia glandifera, the noun 'Agrifolia' being a Medieval Latin form of 'Aquifolium' meaning a holly or holly-leaved oak, and related to the Modern Italian 'Agrifoglio', meaning 'holly'.
Distribution and habitat
The coast live oak is typically found within 100 km (62 mi) of the Pacific Ocean, living on coastal hills and plains and preferring soil with good drainage as well as proximity to perennial streams. It often lives in communities with other native oaks and sometimes in mixed evergreen forests. It generally prefers elevations less than 700 m (2,300 ft), but can be found as high as 1,500 m (4,900 ft) in some places. The oak typically enjoys the climate of near-coastal environments; it has a higher-than-average tolerance for airborne salinity, allowing coastal fog to make up for the lack of rain during much of the year.
Ecology
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