I agree ... Salix caprea aka Goat Willow ... they have seeds like thistledown that float on the air and often find their way into pots and containers where they grow, leading folk to believe they're something they've planted or bought ... they're good for wildlife but grow very large and unless you have several acres of paddocks or wildlife gardens you really don't want it.
“I am not lost, for I know where I am. But however, where I am may be lost.” Winnie the Pooh
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Male catkins below.
Recommend that you get rid of it before it turns into a tree.