Flower:

Round clusters ¾ to 1 inch in diameter densely packed with 100 to 200 flowers. Clusters are single at the ends of stalks up to 4 inches long at branch tips and arising from upper leaf axils. Flowers are white, trumpet shaped, about 1/3 inch long with 4 slightly spreading lobes, sometimes 5. Projecting from the tube is a long, straight, white style surrounded by 4 short stamens, giving the cluster a pincushion-like appearance. The calyx surrounding the base of a flower is light green, 4 lobed, and much shorter than the floral tube.

Leaves and stems:

Leaves are simple and opposite, occasionally whorled in 3s, egg-shaped to oblong-elliptic, 2½ to 6 inches long, 1 to 2¾ inches wide with a sharply pointed tip, and rounded to tapering at the base. The upper surface is hairless, dark green and shiny, the lower surface paler, sometimes with sparse hairs on major veins. Edges are toothless and may be fringed with minute hairs. The leaf stalk is hairless and up to ¾ inch long.

At the base of the stalk is a pair of triangular appendages (stipules) about 1/8 inch long. Twigs are green to reddish with scattered whitish lenticels (pores). Lateral buds are embedded in the bark and appear as a swelling or small pimple above a leaf scar.

Older bark becomes gray-brown and flaking. Lower stems are up to 4 inches diameter. Main stems are typically multiple from base, often forming colonies from root suckers, and have a rounded but irregular crown.

Fruit:

The fruiting head is ¾ to 1 inch diameter at maturity and usually persists through winter. A flower develops into a cone-shaped, 2-sectioned nutlet, the calyx persisting at the tip and turning from green to reddish to dark reddish-brown with age.

Nutlets are thick-walled and leathery, ¼ to 3/8 inch long, each section containing a single seed. Seeds are elliptic to cone-shaped, brown with a whitish, fleshy appendage at the tip.

Notes:

A coarse shrub or small tree, Buttonbush is distinctive when either flowering or fruiting; the pincushion-like flower clusters or balls of nutlets make it easy to identify. A common shrub in the eastern half of North America as well as the southern border states and into northern California, it's found in a wide range of wet habitats, but in Minnesota, where it reaches the edge of its eastern range, it is mostly restricted to floodplains of the Mississippi and St. Croix rivers with few populations on or near lake shores. It attracts many pollinators and has gained some interest in the nursery trade, though requires adequate moisture and continued pruning to maintain a pleasing form and to keep the root suckers under control. Some references note 2 varieties, var. pubescens with hairy leaves and var. occidentalis with mostly hairless leaves, but these are not recognized in Minnesota.