Buttonbush or button willow is an obligate wetland woody shrub. It is good for conservation plantings. The seed is eaten by eight species of waterfowl, the twigs by three species of mammal, and the flower heads are very attractive to bees and butterflies.

A cultivar "Keystone" has been released by the USDA's, Plant Material Center in Big Flats, NY.

Its native range is eastern North America. It grows from 3-8 feet tall and does best in full sun. The striking flower is sweetly fragrant. The leaves, 3-6 inches long, are opposite or whorled.

After flowering, the buttonbush heads (flower clusters) turn into ball-shaped "buttons." Likewise, the female flowers of American sycamore (Platanus occidentalis) form closely packed, ball-like, heads attached to a long, slender, thread-like stem. By October the buttonbush heads develop into a "buttonball", composed of many hairy nut-like seeds. These seed balls give rise to the common name buttonwood or buttonball tree. The terms under which the New York Stock Exchange was formed is called the 'Buttonwood Agreement' (note 1), because it was signed under a buttonwood tree.

Reference:
1) Wikipedia Article