Ask Mr. Smarty Plants

Cephalanthus occidentalis (common buttonbush) does indeed spread and become a multistem shrub as long as it is near water. Here's what is on our webpage.

Common buttonbush is a multi-stemmed shrub which grows 6-12 ft. or occasionally taller. Leaves in pairs or in threes, petiolate; blade up to 8 inches long, ovate to narrower, sometimes 1/3 or less as wide as long, with a pointed tip and rounded to tapered base, smooth margins and glossy upper surface, lower surface duller. Glossy, dark-green leaves lack significant fall color. Flowers small, borne in distinctive, dense, spherical clusters (heads) with a fringe of pistils protruded beyond the white corollas. Long-lasting, unusual blossoms are white or pale-pink, one-inch globes. Subsequent rounded masses of nutlets persist through the winter. Trunks are often twisted. Spreading, much-branched shrub or sometimes small tree with many branches (often crooked and leaning), irregular crown, balls of white flowers resembling pincushions, and buttonlike balls of fruit.

Buttonbush is a handsome ornamental suited to wet soils and is also a honey plant. Ducks and other water birds and shorebirds consume the seeds.

Common buttonbush is a spreading, multi-branched shrub or sometimes small tree with many branches (often crooked and leaning), irregular crown, balls of white flowers resembling pincushions, and buttonlike balls of fruit. Buttonbush is a handsome ornamental suited to wet soils and is also a honey plant. Ducks and other water birds and shorebirds consume the seeds.

The USDA has additional information about Cephalanthus occidentalis on their webpage.