Verdun wrote (see)
Astilbes or astrantias, primulas,, arum lilies, acorus, and a lovely grass called hackanochloa would grow there I think. Tina. Some ferns do like lot of moisture.
Hackenochloa one of my faves Verdun, and of course marsh marigolds and many other marginals/bog plants could do well. Ligularias also. Spartina is a grass which does well with fluctuating water levels and is very attractive with arching green/creamy strappy leaves. I got it from aspecialist nursery a long time ago but you don't often see it. Chicky, Etoile Violette is gorgeous, I will definitely be planting that again. Rouge Cardinal is lovely as well- slightly redder than EV.