QUERCUS

Genus of about 530 species of deciduous, semi-evergreen or evergreen trees and shrubs in the beech family widely distributed in woodland and scrub in the northern hemisphere extending to tropical latitudes.

Some deciduous species give excellent autumn colour.

Because of land use changes and climate change many species are under acute threat. In the highlands of Mexico, Central America and the northern Andes forests have been cleared to make coffee plantations and cattle ranching. Pine forests are invading oak in the Indian Himalayas because of temperature rise.

In the UK, Phytopthora ramorum (so-called sudden oak death), a bacterium thought to cause acute oak decline and the oak processionary moth, which causes defoliation, are modern threats.

Represented in the UK by 2 natives, Sessile or Durmast (Q. petraea), stalked leaves and unstalked acorns and English or Pedunculate (Q. robur) with very short stalks on leaves and long stalks on acorns.

Two other oaks commonly seen are the holm oak (Q. ilex), evergreen, and the Turkey oak (Q. cerris) which was introduced, mistakenly, as a source of good timber.