- This article is about a genus of plants. For the wrasse genus see Decodon (fish)
Decodon verticillatus, the sole species in the genus Decodon, is a flowering plant in the Lythraceae family. It is commonly known as waterwillow or swamp loosestrife. It is endemic to wetlands in the eastern half of the United States.
Waterwillow is a clump-forming shrubby perennial that grows in swamps or shallow water. The stems are arching, angular, smooth and woody near the base, and up to eight feet tall. They sometimes root at the tip when they bough over and touch the mud. The leaves are lanceolate, either in opposite pairs or in whorls of three or four. They are up to five inches long and one inch wide, smooth above and hairy beneath, on very short stalks. The rose-pink flowers grow in axillary clusters. The calyx is cup shaped, the corolla under an inch wide with usually five petals narrowing at the base. The ten stamens are projecting with five longer than the rest. There is one pistil, one style and a superior ovary. The fruit is a spherical dark brown capsule with numerous reddish seeds. Flowering takes place in June and July.
Waterwillow is found in swampland, in ditches, besides streams and in shallow water at the edges of ponds and lakes. It often forms thickets and occurs in the United States from Maine to Florida and west to Minnesota, Tennessee and Louisiana.
- The larva of the hydrangea sphinx, Darapsa versicolor, feeds on waterwillow.
- The larva of the waterwillow stem borer moth, Papaipema sulphurata, feeds on waterwillow.
- Homer D. House, Wild Flowers Of New York University of the State of New York, 1918
- Northern Prairie Wildlife Research Center
- Swamp Loosestrife; Willow-Herb - Decodon Verticillatus
- Bill Oehlke
- Lloyd Center for the Environment