I bought this water plant as Persicaria amphibia (amphibious bistort) which I can now see it is not.
It has a buttercup flower,so what is it please!
Looks to me like Lesser Spearwort ... we bought some for our wildlife pond ... it has a lovely perfume if you get up close ... I really like it.
It does look nice and think it will suit my pond,just a bit miffed it wasn't what I thought I bought!