Buttonbush (Cephalanthus occidentalis) of the Madder or Coffee (Rubiaceae) family is a deciduous wetland shrub with many small radiating flowers packed into tight spherical heads. It occurs across a large area of the eastern U.S. from the Big Bend area of Texas, northeastward into southeastern Minnesota, and east to the Atlantic and Gulf Coasts. There are also disjunct populations in portions of Arizona and California. In Arkansas, it occurs statewide. The genus name is from Greek words for “head” and “flower.” The specific epithet, from Latin, translates to “of the West.” Other common names include button-willow and honey-bells. Preferred habitat is sunny to shaded wetlands that may be subject to periodic and even extended flooding, such as swamp and pond margins, marshes, swales, floodplains, and drainages.
Buttonbush is an upright to spreading woody shrub––the only woody member of the Coffee family in Arkansas––with a typical height of 3 to 8 feet, but may attain small-tree size especially in heavy shade. New branches are smooth and green with white lenticels. In subsequent years, branches darken to brown or reddish brown and lenticels become corky. Ultimately, trunks and branches become gray and fissured.
Simple leaves, developing in late spring, occur as opposite pairs or whorls of three or four, growing from swollen nodes. Blades are ovate to elliptical with entire margins, acuminate tips, and rounded to narrowed bases. Leaves expand to 7 inches long and 4 inches wide, including slender 1½ inch-long petioles. The upper leaf surface is a shiny dark green (less shiny later in growing season), while the lower surface is duller. Ascending petioles are reddish to brownish. Triangular, persistent, reddish stipules, to about ⅛ inch long, occur beside the petioles and leave minute line-scars around the nodes.
The inflorescence consists of showy, fragrant, spherical flower heads that occur singly at the branch tips and in 2-4 opposite pairs below. Whorls of 3 or 4 may occur and sometimes flower heads and leaves occur in the same whorl. Heads are from ¾ to 1¼ inches in diameter and comprise several hundred small, sessile, tubular, equal-sized flowers. Flowers begin to bloom in early June. All flowers of a head reach anthesis at the same time and, but with up to a dozen heads on a branch blooming successively, the bloom period may extend over a month. After fruits have matured and shed seeds, the peduncles die back to the leaf nodes below.
The ⅓-inch-long fragrant white flowers are composed of a long slender, tubular corolla and a small shallow pale green four-lobed calyx about ¼ inch long. The corolla has four oval, ascending, flared lobes. Single black dots occur outside the tube, where corolla lobes and tube join. Flowers have four short white filaments with brownish yellow round anthers and a white style topped with a light yellow stigma. While the filaments and anthers are positioned at the mouth of the tube; the long styles protrude well above the corolla so that heads at anthesis have a prickly appearance. Filaments are adnate to the tube in its upper portion. The ovaries are inferior––calyx and corolla are attached at the summit of the ovary, not at the base.
After blooming, flowers quickly wilt and drop off to reveal a sphere of empty, sturdy green calyxes. Calyxes gradually shrink to form the squarish indented apex of the fruits. The green heads may become reddish before drying to a light tan and then dark brown. Fruits, ¼ inch long, have straight sides that taper sharply to the base (narrowly conical). The tightly packed head forms a hard, rough sphere with a diameter to about ⅞ inch and may contain more than 250 fruits. With peduncles and immediately adjacent branches dying, dangling fruit heads persist over the winter months. Fruits may contain one or two nutlets, but often ovules do not develop into viable seeds. Fruits are dispersed by birds and water.
In a native plant garden, butterfly garden, or natural area, buttonbush is well suited for a consistently wet to shallow-water or boggy site. It is adaptable to less wet sites, but will need supplemental watering until well established. With its open growth habit, it has a strong structural appearance in winter months. Flowering is more profuse in sunnier sites. Flower heads are very showy and attract butterflies, bees, and many other insects, as well as hummingbirds. Fruits are eaten by ducks and a variety of other birds. Fruit heads, persisting for six months or more, are attractive and distinctive over winter months. A grouping of shrubs is effective in controlling erosion on pond banks. Plants propagate easily from cuttings. It is not an aggressive self-seeder. Buttonbush is a poisonous plant (contains cephalathin).
Buttonbush is the only species of the genus that occurs in Arkansas. Its preferred habitat and the appearance if its spherical flower and fruit heads allow it to be readily distinguished from other shrubs and small trees that have simple, opposite, entire leaves. In addition to its wide range in the Lower 48, the species occurs south of the border, in Mexico and Central America, and to the north in southeastern Canada.
Article and photographs by ANPS member Sid Vogelpohl