Indigobush (Amorpha fruticosa L.)

Family: Leguminosae 

Description and Variation:   Amorpha fruticosa is a shrub that can grow as tall as 20 feet in height and its width is typically twice its height. The branches are firm and woody and the twigs are green and hairy. Each leaf has 13 to 25 leaflets. The leaflets are one to two inches long, resinous, dotted, and hairy. The flowers are terminal on the branches in erect racemes. The fruit is about 1/4 inch long, curved, with resinous dots and contains two seeds each.

Economic Importance:   A. fruticosa is an exotic species often planted as an ornamental that has become naturalized throughout the central and eastern United States and is also reported for Texas, Colorado, and California. Indigobush is still being sold widely through the United States as an ornamental species. In Washington, it is listed on the State Noxious Weed Control List because it has spread along stream corridors in eastern Washington. There is little information about control methods.

Habitat:  Indigobush grows along streams and river corridors and in prairie draws. Because it grows in riparian corridors, we consider it to be a freshwater invasive species.

History:  Indigobush was not reported for the Pacific Northwest by Hitchcock and Cronquist; however, records in Washington date back to 1974 at Rooks Park, Walla Walla County. Indigobush has since been reported along the lower Columbia river as far inland as Klickitat County and from Central Ferry on the Snake River. All records in Washington have been from Army Corps of Engineers land.