COMMON NAME

False indigo
Indigobush
Desert false indigo


FULL SCIENTIFIC NAME

Amorpha fruticosa L.


FAMILY NAME COMMON

Pea family


FAMILY SCIENTIFIC NAME

Amorpha fruticosa


IMAGES


Close-up of inflorescence

Habit

Close-up of inflorescences

NOMENCLATURE/SYNONYMS

Synonyms: Amorpha angustifolia (Pursh) Boynt.
Amorpha bushii Rydb.
Amorpha croceolanata P.W. Wats.
Amorpha curtissii Rydb.
Amorpha dewinkeleri Small
Amorpha occidentalis Abrams
Amorpha tennesseensis Shuttlw. ex Kunze
Amorpha virgata Small


DESCRIPTION

Botanical Glossary

Amorpha fruticosa is a shrub that can reach 4 m (13 ft.) in height, but in New England it is usually found to be much shorter. The compound leaves are 15-40 cm (6-16 in.) long, with petioles measuring 2-5 cm (0.75-2 in.). The 4 to over 10 pairs of leaflets are each 2-4 cm (0.75-1.5 in.) long and 1-2 cm (0.4-0.8 in.) wide. These leaflets are on short petiolules, are oval or elliptic in shape and sparsely pubescent on their lower surface. The petiolules are usually pubescent as well. The violet flowers that appear in June-July are in upright narrow racemes that can be clustered or solitary and are 6-20 cm (2.5-8 in.) in length. The individual flowers are 7.5 mm (0.25 in.) long. The calyx tube is 2-3 mm (0.1 in.) long and each of the upper 4 lobes is 0.5 mm (0.02 in.) in length. These lobes are broadly triangular to half-orbicular in shape. The stamens of the flowers are orange-yellow and exserted. The seeds are contained in glabrous pods that have thick stalks. These pods are 7.5 mm (0.25 in.) in length and usually contain 2 seeds. Page References Bailey 559, Fernald 899, Gleason & Cronquist 300, Holmgren 283, Magee & Ahles 650, Newcomb 106. See reference section below for full citations.


SIMILAR SPECIES

Robinia hispida L. (Rosa acacia)
Robinia viscosa Vent. (Clammy locust)
Robinia pseudoacacia L. (Black locust)
Gleditsia triacanthos L. (Honey locust) These species are only likely to cause confusion with Amorpha fruticosa when they are young.


REPRODUCTIVE/DISPERSAL MECHANISMS

Amorpha fruticosa reproduces by seeds, which are dispersed mechanically. Its strong association with waterways and floodplains suggests that water may play a significant role in its dispersal. Some of its dispersal has been due to intentional planting by highway departments because of its tolerance for poor soils and high salinity.


DISTRIBUTION

Amorpha fruticosa is native to the United States, but it is unclear exactly how far its native range extends. It is currently found in all the contiguous states except Montana and Nevada. Fernald (1950) stated that the native range extends northeast to southern Pennsylvania, Ohio and New Jersery. Dirr (1983) reported that it is native as far northeast as Connecticut. In any case, it has spread beyond its historical range in the northeast. It has been imported from Europe and planted horticulturally in southern New England. In New England it is found primarily along the southern coast and up larger river valleys. Along the Connecticut River, it is reported as far North as Holyoke, Massachusetts. It has also been found along riverways as far North as central Maine.


HISTORY OF INTRODUCTION IN NEW ENGLAND

Dirr (1983) reported that Amorpha fruticosa was introduced into North America in 1724, implying that horticultural use beyond its native range began in colonial times. However, precisely when it was brought to New England in this manner is unclear, just as is the exact extent of its native range.


HABITATS IN NEW ENGLAND

,Edge,Floodplain Forest,Herbaceous Wetland,Lake or Pond,Open Disturbed Area,River or Stream,Roadside,Shrub Wetland,Yard or Garden

In New England, Amorpha fruticosa is typically found along riverbanks, flood plains, tidal zones and other areas associated with water. It can occasionally be found in moist open woods. It is also found planted along highways in some sections of southern New England.


THREATS

Amorpha fruticosa can tolerate nutritionally poor soils, most notably because of its association with nitrogen fixing bacteria. It also makes a good highway shrub because of its tolerance for salt. It has the potential to crowd out native species, especially along waterways above the high water level.


DOCUMENTATION NEEDS

Documentation required: A specific photograph or mounted snippet of the flowers or fruits.
Best time for documentation: Summer, fall.


ADDITIONAL INFORMATION

Connecticut Botanical Society
Description and images

Integrated Taxonomic Information System
Taxonomic information about the species

The PLANTS Database
General information and map

Virginia Tech Forestry
Description and images

Washington Department of Ecology
Description and images


REFERENCES

Bailey, L. H.  1949.  Manual of Cultivated Plants.  Macmillan, New York.

Britton, N. L. and A. Brown.  1970.  An Illustrated Flora of the Northeastern United States vol. 2.  Dover Publications Inc., New York.

Dirr, M.A. 1983. Manual of Woody Landscape Plants. Stipes Publishing Company, Champaign, Illinois.

Fernald, M.L. 1950.  Gray's Manual of Botany 8th ed.  Dioscorides Press, Portland OR.

Fire Conference 2000.  Proceedings of the Invasive Species Workshop: The Role of Fire in the Control and Spread of Invasive Species. The First National Congress on Fire Ecology, Prevention, and Management.  Tall Timbers Research Station, Miscellaneous Publication No. 11.

Gleason, H.A. and A.C. Cronquist.  1991.  Manual of Vascular Plants of the Northeastern United States and Adjacent Canada. 2nd ed.  New York Botanical Garden, Bronx, New York.

Holmgren, N.H. 1998. Illustrated Companion to Gleason and Cronquist's Manual.  New York Botanical Garden, Bronx, New York.

Magee, D.W and H.E. Ahles. 1999.  Flora of the Northeast. University of Massachusetts Press, Amherst.

Newcomb, N. 1977.  Newcomb's Wildflower Guide.  Little Brown, Boston.

Ohyama, M., T. Tanaka, M. Iinuma. Jul 1998. A prenylated flavanone from roots of Amorpha fruticosa. Phytochemistry 48 (5): 907-909.

Szentesi, A. 1999. Predispersal seed predation of the introduced false indigo, Amorpha fruticosa L. in Hungary. Acta Zoologica Academiae Scientiarum Hungaricae 45 (2): 125-141.

USDA, NRCS.  2001.  The PLANTS Database, Version 3.1. (http://plants.usda.gov).  National Plant Data Center, Baton Rouge, LA 70874-4490 USA.