Found among normal G.urbanum along hedgerow no other affected, is it a bi colour/variegated?
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4th pic looks like virus, also 2nd.Some variegations are stable viruses,I was told.Could be deficiency but looks too distinct, over to others now please.
I would agree with Hazel that it is a virus.
This is known as 'venal variegation', it happens when the veins of a leaf, it is due to lack of chlorophyll below the leaf. It is caused by various environmental/ weather conditions, which can cause this rare type of variegation. It can be white, yellow, pale green colouration on the veins. Count yourself lucky! If This could stay true on the plant, you will have a new variegated species, but theres also a chance you would lose it! So look after it with your life! I had quite a few unusual variegated plants in the past, so my word of advice, look after it to your best potential!!
Heres a useful link to help you understand about variegation in plants: http://en.wikipedia.org/wiki/Variegation
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