The end of the sun garden closest to the bridge is dominated by perennial sunflower. I don't know what its proper name is; I know it only as perennial sunflower. The purpley leaves of the plant turn upside-down every afternoon, as though it's had enough of the sun -- so its common name really isn't appropriate, methinks.
The sunflower plant doesn't overtake its neighbors, but obedient plant does. The monarda at this end of the garden is being eradicated by obedient plant (one obedient sample in pic #3).