I know of the problem with the purple loosestrife , I have seen it first hand when I lived in Michigan.
Seem like the loosestrife is a very diverse plant.
I have a fringed loosestrife that has a very pretty dark leaf and small yellow flowers. It took me a long time to identify because it is so different than the other loosestrife I have in the garden.
May...dark leaves
June... covered in flowers