About Quercus tomentella Engelm.
Quercus tomentella Engelm., commonly called island oak, is a tree that can reach up to 20 meters (66 feet) in height. Mature individuals have a grayish to reddish brown trunk covered in scaly, furrowed bark. Their twigs are reddish and covered in woolly hairs. The leathery leaf blades are often concave, shaped as oblong lance or oval with either pointed or rounded tips. Leaf edges are either smooth or toothed. The upper leaf surface is dark green; it is lightly hairy when new, and loses these hairs over time. The underside of the leaf is gray-green, coated in woolly hairs that become less dense as the leaf ages. Leaves are usually 7 to 10 centimeters (2 3⁄4 to 4 inches) long, and can sometimes grow up to 12 centimeters (4 3⁄4 inches) long. Acorns of this species grow singly or in pairs. The acorn cup has thick scales and woolly hairs, and grows up to 3 centimeters (1 1⁄8 inches) wide. The acorn nut can reach up to 3.5 centimeters in length, and has a rounded tip.
This species is native to six islands: five of California's Channel Islands (Anacapa Island, San Clemente Island, Santa Catalina Island, Santa Cruz Island, and Santa Rosa Island), and Guadalupe Island, which is part of the state of Baja California. It is a relict species. While it is currently restricted to these islands, extensive late Tertiary fossils found in mainland California show it was once widespread across that region. Recent research has found high genetic variability across many Q. tomentella populations, but this variation is not evenly distributed among populations.
In ecological terms, island oak hybridizes with canyon live oak (Quercus chrysolepis).
