Quercus petraea (syn. Quercus sessiliflora), the Sessile Oak, also known as the Cornish Oak or Durmast Oak, is a species of oak native to most of Europe, and into Anatolia.
The Sessile Oak is a large deciduous tree up to 20-40 m tall, in the white oak section of the genus (Quercus sect. Quercus) and similar to the Pedunculate Oak, Q. robur, with which it overlaps extensively in range. The leaves are 7-14 cm long and 4-8 cm broad, evenly lobed with five to six lobes on each side, and a 1 cm petiole. The flowers are catkins, produced in the spring. The fruit is an acorn 2-3 cm long and 1-2 cm broad, which matures in about 6 months.
Significant botanical differences from Pedunculate Oak Quercus robur include the stalked leaves, and the stalkless (sessile) acorns from which one of its common names is derived. It occurs in upland areas over 300m with higher rainfall and shallow, acidic, sandy soils whereas Quercus robur prefers deeper, richer soils at lower altitude. Fertile hybrids with Quercus robur named Quercus × rosacea are found wherever the two parent species occur and share or are intermediate in characters between the parents.