Latin quercus "oak," from PIE *kwerkwu-, assimilated form of *perkwu- "oak" (see fir).
Examples from the Web for quercus
It grows to a height of about 30 feet, and resembles the Quercus ilex, or evergreen oak, and attains to a great age.
Take as an example C. quercus, which produces the spongy excrescence well known as the common Oak-apple.Omphalos|Philip Henry Gosse
I do not think I saw a specimen of the British Quercus robur of such consummate beauty.Our Hundred Days in Europe|Oliver Wendell Holmes
It affects the bark of species of Quercus, and seems to be associated there with Clastoderma debaryanum.The North American Slime-Moulds|Thomas H. (Thomas Huston) MacBride
It is bought for tanning purposes, but its principal use is to adulterate the bark of another oak (Quercus densiflora).American Forest Trees|Henry H. Gibson