Oh, I forgot to clarify, I'm looking for lythrum salicaria, not the other species. Thanks

Campanula latiloba is practically identical to C.persicifolia. Main difference in cultivation is that C.persicifolia is subject to rust, and C.latiloba is not.

I grow Siberian iris in part sun/part shade and they bloom and grow without problem. There are Cimicifuga (AKA Actea) such as 'Brunette' with dark purple/maroon leaves that do well in part shade, and have white spires of flowers in late summer. Some folks have found them fussy, but I've not had problems. They are quite deer resistant. There are some varieties of clematis that do well in part sun/shade - I'd google for clematis & shade or go to Clematis on the Web and either search or see if there is a list of shade tolerant clematis there. I have one (I think 'Blue Angel') that grows on the east side of my house, and only gets morning sun, though high, bright shade the rest of the day. It is flourishing. I also had a clematis 'Venosa Violacea' which is purple & white that grew well & bloomed in the same part shade garden as the Actea & Siberian iris until the voles ate the roots last winter. :>( Here is a link that might be useful: Clematis on the Web

Tinantia pringlei perhaps.