Where did the willow tree come from?

the willow tree can only be natively found in london, all others are actually a hybrid species made in 1940s to raise moral in the war.

The true willow tree can only exist in london soil due to high levels of lead in the soil left there by the romans. (With the lead sewers)

The willows you see outside of london are actually a cross breed with cabbage. Which is why they have thicking branches. True willows are very thin.