Indigobush (Amorpha fruticosa) is a shrub that can grow as tall as 20 ft. high and its width is typically twice its height. The branches are firm and woody and the twigs are green and hairy. The leaves have 13 to 25 leaflets each. The leaflets are 1 to 2 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 and Distribution
A. fruticosa is considered an invasive exotic species in Washington. According to the Lady Bird Johnson Wildflower Center, Indigobush is native from New Jersey, to Wisconsin, Minnesota and Wyoming and south to Florida, Texas, northern Mexico, Southern California to New Mexico and adjacent Mexico. On the west coast, it was often planted as an ornamental or for bank stabilization. Indigobush is still sold widely as an ornamental species. In Washington, it is listed on the State Noxious Weed Control List because it has spread along stream corridors in both eastern and western Washington. It displaces native riparian area species. There is little information about control methods.
Indigobush grows along streams and river corridors and in prairie draws. Because it grows in riparian corridors, Washington weed scientists consider it a freshwater invasive species.
It 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. It has since been reported along the lower Columbia river as far inland as Klickitat County and from Central Ferry on the Snake River.
Indigo bush is a perennial species that reproduces by seeds. Although the photograph on this page does not indicate that the flowers are very showy, other photographs on the Internet show long clusters of purple flowers that are very attractive. This, along with the fact that indigobush is native in much of the US, is undoubtedly why this plant has been cultivated and being sold as an ornamental species.
Abrams, L. Illustrated Flora of the Pacific States Vol. II. Stanford University Press. Stanford, California. p. 555.
Lady Bird Johnson Wildflower Center - http://www.wildflower.org/plants/result.php?id_plant=AMFR
Munz, P. A. and D.D. Keck. 1970. A California Flora. University of California Press. p. 852.
Native Shrub Production Project. U.S.D.A. Surface Environment & Mining. Coeur d'Alene Nursery.
Nebraska Weeds. 1968. Nebraska Dept. of Agriculture. Lincoln, Nebraska.
Old, Rich. 1984. Plant Notes.
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