Technical Information about Amorpha fruticosa (Indigobush)
Description and Variation
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 2 seeds each.
Economic Importance
A. fruticosa is considered an invasive exotic species in the western United States. It is, however, native to the eastern US. It was often planted as an ornamental or for bank stabilization and has become naturalized in some western states. In addition to Washington, it is also reported for Texas, Colorado, and California. Indigobush is still being 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 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 are considering it a freshwater invasive species.
History
It was not reported for the 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. All records in Washington have been from Army Corps of Engineers land.
Growth, Development, and Reproduction
Indigo bush is a perennial species that reproduces by seeds. Although the photographs on this page do not indicate that the flowers are very showy, other photographs on the Internet show long clusters of purple flowers that are very attractive. This is undoubtedly why this plant has been cultivated and being sold as an ornamental species.
References
Abrams, L. Illustrated Flora of the Pacific States Vol. II. Stanford University Press. Stanford, California. p. 555.
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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