Howard Oakley’s tree series reaches the willow, and Sisley’s 1883 Willows on the Banks of the Orvanne is the canonical portrait: a row of pollarded heads, then river, reeds and poplars, the colours reversing the usual fade of aerial perspective. From there it runs through Ophelia’s willow in Delacroix and Cabanel, Mondrian before abstraction, and Monet’s weeping willow of 1918.