Exotic Species: Scotch Broom

Fabaceae (Pea family)

At a Glance

Scotch broom plant in bloom
Scotch broom is a shrub with bright yellow flowers and stiff, slender branches.

© Anne Tanne

  • Perennial shrub.
  • Strongly angled, green stems.
  • Small leaves occur together in groups of three.
  • Bright yellow flowers in leaf axils.
  • Fruit is a brownish-black pod with hairs only along the seams.
  • Drought-deciduous

Habitat and Ecology

Scotch broom (Cytisus scoparius) is found along the east and west coasts of North America and in Idaho, Montana, and Utah. Native to northern Africa and parts of Europe, it was first introduced to North America on the east coast and was later introduced to California as an ornamental. From the 1850s through the early 1900s, Scotch broom was frequently planted in gardens. Later, it was used for erosion control along highway cuts and fills.

Scotch broom flourishes in full sunlight in dry, sandy soils, but it can survive under a wide variety of soil conditions. However, it does not tend to survive in very arid or cold areas. Scotch broom invades dry hillsides, pastures, forest clearings, dry scrublands, dry riverbeds, and waterways. Several characteristics contribute to its success as an invasive plant: (1) although it loses its leaves during dry conditions, the photosynthetic tissue in its stems allows it to grow throughout the year; (2) its roots host nitrogen-fixing bacteria, which helps the plant to establish in nutrient-poor soils; and (3) it produces abundant seeds that remain viable in the soil for many years. In addition, Scotch broom is slightly toxic and unpalatable to livestock.

Distribution map for Scotch broom
Map of Scotch broom distribution from the USDA PLANTS database (https://plants.usda.gov/java/profile?symbol=CYSC4).

USDA

Description

Scotch broom is a bushy, drought-deciduous shrub that grows three to six feet tall. The green branches are sharply angled with five green ridges, and they are hairy when young and without hairs as they mature. Scotch broom reproduces vegetatively and by seed. The seed pods often open explosively, vaulting the seeds to some distance away. Two adaptations allow the seeds to disperse even further: (1) a hard seed coat that allows the seeds to survive rough transport through water, and (2) a fleshy structure rich in lipids and proteins that attracts ants. The ants carry the seeds back to their nests, creating dense infestations of scotch broom around ant nests. Scotch broom may also be dispersed by goats and horses digesting the seeds.

Leaves
The small leaves occur in groups of three. Each leaf is oblong and pointed at both ends. During drought, Scotch broom sheds its leaves.

Yellow Scotch broom flowers (left) and blackish-brown fruit pods (right)
LEFT: Scotch broom flowers. RIGHT: The fruits are blackish-brown pods with hairs on the seams.

Flowers © Steve Dewey / Utah State University; Fruit pods © Gil Wojciech, Polish Forest Research Institute.

Flowers and Fruits
The bright yellow flowers are shaped like pea flowers. Each flower is usually located in the space between the leaf stem and the branch. The flowers bloom between April and June.

The fruit is a flat, brownish-black pod. The pod has long hairs along its seams, but nowhere else. The seeds inside the pod are shiny and greenish-brown to black in color.

Etymology

Cy’tisus comes from the Greek word kutisus, which was the name for a kind of clover. Scopar’ius means “broomlike”.

Ethnobotany

The dense mass of slim stems was once cut and made into brooms. Scotch broom was also used for a variety of other purposes, such as flavoring beer with a bitter taste, making a diuretic from an infusion of the leaves, and tanning leather.

Similar Species

Scotch broom can be confused with French broom (Genista monspessulana), Portuguese broom (Cystisus striatus), and common gorse (Ulex europaeus). All species occur in similar habitats, but their appearances differ slightly. French broom has pods with hairs all over and stems that are not ridged or green. Portuguese broom has paler yellow blossoms and silver seedpods that are densely covered with white hairs. Common gorse also has bright yellow flowers, but it is spiny and has small, hairy seedpods.

Control Methods

References

Bossard, C. 2000. Cytisus scoparius in Bossard, C. C., J. M. Randall, and M. C. Hoshovsky, editors. Invasive plants of California’s wildlands. University of California Press, Berkeley, CA. 

Charters, M. L. 2009. California plant names: Latin and Greek meanings and derivations. Available at http:// www.calflora.net/botanicalnames (accessed 24 March 2010).

Hoshovsky, M. 1986. Cytisus scoparius and Genista monspessulana in Element Stewardship Abstracts. The Nature Conservancy, Arlington, VA. Available at: http://www.imapinvasives.org/GIST/ESA/esapages/ documnts/cytisco.pdf (accessed 24 March 2010).

Meyer, S. E. 2008. Cytisus scoparius (L.) Link: Scotch broom. Pages 466-467 in Bonner, F. T., and R. P. Karrfalt, editors. The Woody Plant Seed Manual. Agricultural Handbook Number 727. U.S. Department of Agriculture, Forest Service, Washington, DC. p. 466-467. 

Zouhar, K. 2004. Cytisus scoparius, C. striatus. in Fire Effects Information System. US Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. Available at

https://www.fs.fed.us/database/feis/plants/shrub/cytspp/all.html 

 

 

Prepared by Kelly Reeves, Southern Colorado Plateau Network Inventory and Monitoring Program, 2010.

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