Chestnut leaved oak - Quercus castaneifolia. Winter branches

Quercus castaneifolia, the Chestnut-leaved Oak, is a species of oak in the turkey oak section Quercus sect. Cerris. It is native to the Caucasus and Alborz mountains of Iran, and resembles the closely related Turkey Oak in appearance.

It is a deciduous tree growing up to 35 m tall, with a trunk up to 2.5 m diameter (exceptionally up to 50 m tall with a trunk up to 3.5 m diameter). The leaves are 10-20 cm long and 3-5 cm wide, with 10-15 small, regular triangular lobes on each side. The flowers are wind-pollinated catkins; the fruit is an acorn, maturing about 18 months after pollination, 2-3 cm long and 1.5-2 cm broad, bicoloured with an orange basal half grading to a green-brown tip; the acorn cup is 2 cm deep, densely covered in soft 4-8 mm long 'mossy' bristles. The acorns are very bitter, but are eaten by jays and pigeons; squirrels usually only eat them when other food sources have run out.

It was introduced to England in 1846, but remains relatively rare in collections despite being a vigorous grower. A tree from the original introduction is at the Royal Botanic Gardens, Kew.

The cultivar Quercus castaneifolia 'Green Spire' has been selected for erect growth.

An oak is a tree or shrub in the genus Quercus ( /ˈkwɜrkəs/; Latin "oak tree"), of which about 600 species exist. "Oak" may also appear in the names of species in related genera, notably Lithocarpus. The genus is native to the northern hemisphere, and includes deciduous and evergreen species extending from cold latitudes to tropical Asia and the Americas.

Oaks have spirally arranged leaves, with a lobed margin in many species; some have serrated leaves or entire leaves with a smooth margin. Many deciduous species are marcescent, not dropping dead leaves until spring. The flowers are catkins, produced in spring. The fruit is a nut called an acorn, borne in a cup-like structure known as a cupule; each acorn contains one seed (rarely two or three) and takes 6–18 months to mature, depending on species. The live oaks are distinguished for being evergreen, but are not actually a distinct group and instead are dispersed across the genus.