A copper beech is a beech tree where the leaves turn increasingly dark towards purple over the course of a spring and summer. The process is affected by sunlight. I know this to be the case from repeated observation of one of the copper beech trees in the Botanic Garden in Cambridge. The side facing the sun darkens noticeably more quickly than the side in the shade. Eventually though the leaves on the whole tree turn purple.
So now look at this copper beech where a section of it has reverted to the green leaves of a ‘normal’ beech tree. I’ve never seen that before and I don’t know whether it is the only one in the whole wide world.
Photograph Works 