Quercus × macdonaldii,[1] [2] formerly Quercus macdonaldii, with the common names MacDonald's oak and Macdonald oak, is a rare hybrid species of oak in the family Fagaceae.
The tree is between 5 and 15 meters tall, with scaly bark on the trunk. The twigs are gray and tomentose. The leaves are between 4 and 7 centimeters in length, the blades are oblong to obovate, and adaxially glabrous to sparsely hairy. The petioles are between 3 and 10 millimeters. The fruits cup is between 10 and 20 millimeters long and 6 to 10 millimeters deep. The nuts are between 20 and 35 millimeters long and conic-oblong or ovoid. The flowering time is between the months of March and May.[3]
The tree is endemic to the California Channel Islands, on Santa Cruz Island, Santa Rosa Island, and Santa Catalina Island, in Southern California.[1] It is found in chaparral and woodlands habitats in canyons and slopes below 600m (2,000feet).[1]
The plant was reclassified as Quercus × macdonaldii, a naturally occurring hybrid of Quercus lobata and Quercus pacifica, or possibly other oak species.[1] [2] [4] Both parents are placed in section Quercus.[5] It is considered a species by Greene but derived from hybrids involving Quercus pacifica, Quercus lobata, and possibly others.