Asclepias comes up in
formatting link
?sourceid=navclient&q=%225+feet%22+perennialKniphofia gets tall but none for zone 4 probably... cow parsnips are big. angelica. maybe scan the apiaceae?
formatting link
stenanthia (east n amer.)
thistle family
there are huge grasses and some sedges get big...
THE USE OF ORNAMENTAL GRASSES IN THE LANDSCAPE ... The popularity of ornamental grasses gained momentum in the early 80's when Wolfgang Oehme and Jim van Sweden, two Washington DC landscape architects, began ... sudan.cses.vt.edu/html/Turf/orngrass.htm
they use(d) a lot of tall wet plants
another wet lover:
formatting link
formatting link
weedy
formatting link
sinensis 'Strictus' (porcupine grass) Many grasses are very easy to grow. This one has yellow and gold horizontal bars on its leaves. Silvery plumes in fall, ornamental throughout winter; grows up to 8 feet tall. USDA: 5 to 8/Sunset: all zones. Full sun. Propagate by division. Caution: Miscanthus sinensis is beginning to turn up on invasive plant lists in Northeastern and Middle Atlantic states
"Berberis fendleri" probably conforming to the common overblown description of plants:
formatting link