Oak, Autumnal colours of Aspen and Oak leaves in pond near Alpine, Oregon, USA.

Lone oak tree in field, Wilsonville, Oregon, USA.

Oak, Pin oak, Quercus palustris, Studio shot of backlit leaves.

Oak, Pin oak, Quercus palustris, Studio shot of backlit leaves.

Oak, Common oak, Quercus robur, Autumn leaves covering fallen acorns.

Oak, Acorn, Quercus, Close up of green acorns growing on the tree.

Oak, Quercus robur, Acorns growing on the branches of tree in late summer.

Oak, Common oak, Quercus robur, Side view of fairly mature tree with no leaves, silhouetted against the misty dawn sky in an English field.

Sessile oak, Quercus petraea, Aerial view of many wet, fallen brown leaves and an acorn.

Sessile oak, Quercus petraea, Front view of a sprig of pale new spring leaves against pale green.

Common oak, Quercus robur, Side view of upper branches of some trees with ivy climbing up the trunks.

Oak, Quercus robur, Spangle galls, Neuroterus quercusbaccarum on common oak, Close view of two backlit leaves showing the eggs of this parasitic wasp.