If you drive by the Fern Valley Meadow you can see this plant from 100'. Actually, I can see it from 100', so if you have average eyesight you ought to be able to see it from twice as far.
Good plant that favors wetlands but tolerates average garden moisture. It's a butterfly magnet drawing swallowtails (see photo to right) reliably when it blooms in late summer. Because it is tall, up to 8', it works well at the back of a deep border, or as an accent plant. Very nice informally along a fence. Resistant to pests and diseases, it will benefit from an occasional soaking in a dry summer.
If 8 feet is too much for you there is a selection of a small species of Eupatorium; 'Little Joe' that only grows to 3-5 feet.