The London plane is the perfect city tree, dealing with the street pollution by absorbing it into it's bark, which it then sheds like battered pieces of armour. This is what gives it it's mottled camouflage look.
Planted in great numbers in the mid 19th century to help soak up the soot and dust of the gathering industrial revolution, the London Plane remains invaluable. Bizarrely it may be their very ubiquity that renders them invisible to most people. Spot one and give it thanks for making your city a little more breathing space.