Oaks are in the genus Quercus which is in the Beech family. There are more than 600 species worldwide. There are  two native oaks in Britain, the English Oak  and the Sessile Oak . Three more oaks are shown here but there are many more species in parks, urban settings or botanical gardens in Britain. These five species show many of the key characteristics of the oak genus.  Leaves are often but not always lobed, male and female flowers are on the same tree. Male flowers are on catkins and release pollen onto the wind. Female flowers are tiny and difficult to see. Fruits are in the form of acorns with nuts sitting in ‘cups’ 

English Oak tree in mid May
The English Oak is the dominant tree in most of Britain, particularly on the richer soils in valley bottoms. It has been planted everywhere in parks, gardens, deer parks and woods. The English Oak is also known as the Pedunculate Oak because its acorns have stalks (known as ‘peduncles’ by botanists).
sessile oak tree in midsummer
The Sessile Oak is also known as the Durmast Oak, a name that is possibly related to the feeding of pigs on acorn and beechnuts, known as ‘mast’. In Britain it is more common than the English Oak in upland areas in the North and West and is often found in woodlands on well-drained hillsides. 
Turkey Oak tree
The Turkey Oak is native to Southern Europe and Turkey and was introduced to Britain in 1735. At the time it was thought that it would be a fast-growing source of timber. In fact the wood turned out to be too brittle but the tree has since spread and is frequently found in parks, woods and hedgerows.
Holm Oak tree
The Holm Oak is an evergreen oak – revered by the Ancient Greeks – introduced from Southern Europe to Britain in about 1500. It is now common in parks and gardens. Its leaves vary in shape, with some looking like holly leaves. Holm is an old word for Holly. Its acorn sits in a cup that looks like it is covered in felt. Male catkins hang down in early summer.
Cork Oak tree
The Cork Oak is an evergreen tree that is native to southern Europe and north-west Africa. It was introduced to Britain in the 1690s. The tree is cultivated in its native lands for its bark, which provides a renewable source of cork for wine bottles and flooring.
english oak leaf with ears and no stalk

The English Oak leaf  has a very short stalk, hidden by two small leaves known as “ears” at the base of the leaf.

seesile oak leaf with long stalk

The  Sessile Oak leaf  has  a long stalk.

The Turkey Oak leaf  has deeply cut lobes

Holm Oak evergreen leaves are glossy

Cork Oak evergreen leaves have small lobes.

english oak male catkins

English Oak male catkins in May

english oak female flowers

Sessile Oak male catkins in May

Turkey Oak male catkins in May

Holm Oak male catkins in May

english oak acorns

Cork Oak male catkins in June

english oak acorn on a long stalk or peduncle

An English Oak acorn, which is on a long stalk called a peduncle.

sessile oak acorns no stalk

Sessile Oak acorns have no stalk. They sit on the shoot like this – a feature that is known as ‘sessile’ by botanists.

Turkey Oak acorn with its whiskered ‘cup’

Holm Oak acorn 

Cork Oak acorn