Calla lilies - they grew beautifully in my CA bog garden. You also might try some hydrangeas at the edges. Hydrangeas have a reputation of not wanting to be waterlogged, but they grew just fin in our CA bog. We also had the tall iris - probably almost native in your zone. If you want something big and dramatic, try something in the Gunnera Dinosaur, Plants Dinosaur, family! That should improve the view! lol

Petasites doesn't need wet soil - just moist soil. It will grow perfectly well under ordinary garden conditions........maybe too well!! If growing it in a tub, which is an excellent way to curb its aggressive spread (bamboo barrier will work also), you want to drain holes (a few) and fill with regular garden soil. The tub, even with drain holes, will help to maintain a pretty damp growing environment in addition to keeping the plant from taking over the landscape.

I have creeping jenny growing around my bog. I love the bright green/ yellow pop of color. I am not sure which kind I have but it is very lush and keeps any weeds at bay. I am not sure if it is hardy in your area though, I am in zone 8.

The pleated leaves strongly suggest the genus Cypella. C. aquatilis is rated Zone 8 so it's possible.