Family: Fabaceae

Origin, Description & Uses:
Scotch broom is a woody shrub native to western and central Europe. It was introduced to many parts of the world, including Hawaiʻi, as an ornamental plant and for erosion control. This fast-growing shrub typically reaches 6–10 feet tall and is recognized by its bright yellow, pea-like flowers and slender green stems. It thrives in cool, upland environments and nutrient-poor soils, and has been planted along roadsides and in pastures for its showy blooms and ability to quickly cover disturbed ground.

Risks & Threats:
In Hawaiʻi, Scotch broom is naturalized and considered high risk due to its aggressive growth and prolific seed production. Each plant can produce thousands of long-lived seeds that remain viable in the soil for decades, enabling it to rapidly invade open areas, pastures, roadsides, and native forests—especially in higher elevation regions. Dense thickets crowd out native vegetation, alter soil nutrients by fixing nitrogen, and increase fire risk by adding flammable woody material to the landscape. Because it possesses traits that are cause for concern and could detrimentally impact tropical island ecosystems, it is not recommended for planting. Gardeners and land managers are encouraged to choose low-risk or native alternatives to help protect Hawaiʻi’s unique natural resources.

High Risk Traits:

• Environmentally versatile (elevation range exceeds 1000 m)
  
• Widely naturalized (including Hawaii Island)
  
• A weed of forestry plantations
  
• An environmental weed
  
• Related Cytisus species have become invasive
  
• Toxic to cattle
  
• Increases fire hazard with flammable biomass
  
• Tolerates many soil types
  
• Can from dense monocultures that exclude other vegetation
  
• Limited self-compatibility
  
• Accidentally and intentionally dispersed by seeds
  
• Prolific seed production
  
• Forms a persistent seed bank
  
• Resprouts after damage from cutting or fire

Low Risk Traits:

• May be limited to higher, cooler elevations in tropical island ecosystems
  
• Unarmed (no spines, thorns or burrs)
  
• Palatable to goats and sheep
  
• Intolerant of heavy shade
  
• Does not spread vegetatively
  
• Valued as an ornamental in some locations
  
• Herbicides provide effective control under certain circumstances