Northern Prairie Wildlife Research Center
Buttonbush (Cephalanthus occidentalis)
- Family: Madder (Rubiaceae)
- Flowering: June-August.
- Field Marks: Buttonbush is the only shrub that has whorled leaves and flowers and fruits in spherical heads.
- Habitat: Swamps, lakes, ponds, low woods, marshes.
- Habit: Shrubs, up to 10 feet tall.
- Stems: Much branched, smooth or less commonly hairy.
- Leaves: Opposite and/or whorled, oblong to ovate, pointed at the tip, tapering to the base, without teeth, smooth, up to 6 inches long, up to 4 inches wide.
- Flowers: Many, crowded into spherical heads up to 1 1/4 inches in diameter, white.
- Sepals: 4, green, united into a short tube.
- Petals: 4, white, united into a slender tube 1/4-1/3 inch long.
- Stamens: 4, attached to the corolla tube and not exserted beyond it.
- Pistils: Ovary inferior; styles protruding beyond the corolla tube.
- Fruits: Many nutlets crowded into a spherical head, each nutlet 1/4-1/3 inch long, broadest at the top.
- Notes: It is reported that the leaves are poisonous if eaten by most animals.
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