Buttonbush is a woody shrub (3-10 feet tall) that occasionally grows into a small tree and can be found above water or in water up to 4 feet deep. It has shiny dark-green spear-or egg-shaped pointed leaves 3 to 6 inches long. The leaves are opposite or whorled in 3's or 4's along the stem. Flowers of buttonbush are easily identified by their greenish-white tube flowers in dense ball-shaped clusters about 1 inch in diameter. Seed heads are brown.
http://aquaplant.tamu.edu/database/emergent_plants/buttonbush.htm