Sunday, March 13, 2011

Quercus douglasii - Blue Oak

Quercus douglasii: Quercus the classical Latin name for the oak; douglasii, named for David Douglas (1798-1834), a Scottish collector from the Horticultural Society of London looking for North American plants that could grow in English gardens.

Native to California's Central Valley and foothills. Slow growth to 30-50' tall or more with a 40-70' spread, developing a broad, low-branching, rounded canopy, either leaning or slightly bent, and a heavy clear trunk.

Leaves are alternate, simple 1 - 1 1/2" long by 1/2 - 3/4" wide, dull bluish green, variable from broad oval to almost squarish, with scalloped edges, blunt, often bristle-tipped ends , sparsely covered with minute star-shaped hairs, often with harmless red gall-like warts on the uppersides, lighter undersides with very fine tiny soft hairs at midveins and branches and pastel pinkish orange or dull yellow fall color. Leaves are smaller and bluer than Q. lobata, which grows alongside.

Yellowish-green tassel-like flowers occur in early spring.

Acorns are deep brown, conical, 1/2 - 1 5/8" long by 3/8 - 3/4" wide, with a rounded, short-tipped end, a thin scaled cup covering 1/8 - 1/4 of the base of the nut, from a short-stalked base, maturing in fall of the first season, and occurring in profusion on healthy trees.

Brittle young twigs are dull gray to reddish brown with a slight minute hairiness. Bark is rather thin, light ashy gray with narrow ridges, peeling off easily in thin flakes.

A highly desirable native oak that tolerates valley and foothill heat and seasonal drought. Longevity estimated to be 200-300 years.

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