Oaks
What are they?
The oaks are a very diverse group of trees with many species around the world, particularly in North and Central America. In Britain we have just two native species, but a number of other species have been widely introduced as ornamentals and for forestry. Oaks are very variable in appearance and the group includes both evergreen and deciduous species, trees with simple leaves and trees with leaves that are deeply lobed, but they are all instantly recognisable by their fruits which are known as acorns.
Where are they found?
Native oaks are widespread throughout East Anglia in most habitats and are also widely planted. A number of introduced species may be found where planted in most kinds of urban and suburban habitats as well as in parkland and roadsides in more rural areas.
Identification
As a group, oaks can be identified by their distinctive fruits (acorns) combined with their winter twigs which have distinctive bud clusters at their tips. Individual species can be recognised fairly easily by looking at their leaves, buds and details of the cups that hold the acorns.
Pedunculate Oak Quercus robur
Widespread and common throughout the region. A native tree, forming mature woodland on heavier soils and scrub habitats on thinner, drier soils. Also widely planted in hedgerows and parkland habitats. Flowers April to May. Leaves hairless and with distinctly lobed bases and rather short stalks. Acorns carried in clusters of 1-5 on a common stalk (a peduncle).
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Sessile Oak Quercus petraea
A native tree mostly of the granite-based soils of western and Northern Britain; scarce in East Anglia on the acidic gravels of the Holt-Cromer ridge and south and east Suffolk. Also occasionally planted elsewhere. Flowers April to May. Leaves with star-shaped hairs on the underside and with unlobed bases. Acorns stalkless or with an only very short peduncle.
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Hybrid Oak Quercus x rosacea
The hybrid between Pedunculate and Sessile Oaks is occasionally recorded from areas where the two parents can be found together. Leaves intermediate between the parents but very variable; typically they will show a slightly broader base to the leaf thatn that of Sessile Oak, but with a scattering of star-shaped hairs on the underneath.
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Turkey Oak Quercus cerris
Introduced as an ornamental from south-east Europe and widely planted on roadsides and in hedgerows. Flowers May. Leaves relatively narrow and with sharply angled lobes. Acorns with distinctly bristly cups and winter twigs readily told by the bristly bracts between the buds.
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Hungarian Oak Quercus frainetto
Introduced as an ornamental from south-east Europe and occasionally found as an amenity tree. Flowers May. Leaves relatively large, up to 25cm in length; sharply lobed and distinctly narrowed at the base.
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Holm Oak Quercus ilex
Introduced as an ornamental from southern Europe and very widely planted on roadsides and in parks, cemeteries and amenity areas. Readily grows from acorns planted by Jays or squirrels and is widely naturalised in coastal dunes and some parkland areas. Flowers May. Grows to become a large and broadly spreading, evergreen tree. Leaves tough and extremely variable, usually being broad and prickly (like holly leaves) on shaded branches and young trees, but typically unlobed on mature trees in sunny situations.
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Lucombe Oak Quercus x crenata
Introduced as an ornamental. A hybrid between Turkey Oak and Cork Oak which occurs naturally in the wild in southern Europe but UK plants are typically artifical hybrids from horticultural stock. Rare, but occasionally found where planted in larger parks or cemeteries. Flowers May-June. Being a hybrid between a deciduous species and an evergreen one, this poor tree appears confused and individuals often drop their leaves in February! Horticultural crosses have been made several times and there is much variability in their bark type and the appearance of their leaves (and the timing of leaf drop). Trees show a range in the amount of corkiness of the bark, in the shape and size of the leaves and in the acorn cups and winter buds, according to the amount of influence of each parent.
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Turner's Oak Quercus x turneri
A hybrid of horticultural origin and occasionally found in parks or cemeteries where planted as an ornamental. A hybrid between Pedunculate Oak and Holm Oak. Flowers May-June. A hybrid between a deciduous species and an evergreen one and very variable in the appearance of its leaves.
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Cork Oak Quercus suber
Introduced from southern Europe as an ornamental. Doesn't do well in UK winters and the handful of trees are all rather small, in parks or cemeteries. Flowers May-June. An evergreen tree, famous for its bark which is harvested in the Mediterranean to provide cork.
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Northern Red Oak Quercus rubra
Introduced from North America and planted occasionally in forestry blocks, or less often as an ornamental. Flowers May. A deciduous tree with leaves averaging much larger than those of our native oaks (up to 20cm in length) and more sharply angled, with bristle-tips at the ends of the leaf lobes. Underside of leaves hairless except for small tufts of brownish hairs in the vein axils. This is an important distinction from Black Oak (Quercus velutina) which is hairy on the leaf undersides (especially young leaves) and is occasionally planted in the UK, though not yet recorded in East Anglia. Leaves cut no more than half way to the mid vein. Bark only lightly fissured.
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Scarlet Oak Quercus coccinea
Introduced from North America and planted occasionally as an ornamental. Flowers May. A deciduous tree with leaves averaging larger than those of our native oaks (up to 20cm in length) and more sharply angled, with bristle-tips at the ends of the leaf lobes. Underside of leaves almost hairless with just brownish hairs in the vein axils. Leaves often deeply cut more than half way to the mid vein. Winter buds somewhat elongated and pointed. Bark fissured and craggy but not flaking easily.
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Pin Oak Quercus palustris
Introduced from North America and planted occasionally as an ornamental. Flowers April to May. A deciduous tree, closely resembling Scarlet Oak but the underside of the leaves have more conspicuous tufts of brownish hairs in the vein axils and the leaves tend to be even more deeply cut. Winter buds short and rounded. Bark usually less fissured and craggy than Scarlet Oak and lower branches of younger trees typically sweep slightly downwards.
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