Family: Fabaceae

Origin, Description & Uses
Ulex europaeus (gorse) is a dense, evergreen, thorny shrub native to Madeira, western and central Europe, and Algeria. It is easily recognized by its rigid, spiny branches and bright yellow, pea-like flowers that bloom over an extended season. Gorse has historically been cultivated as a living hedge, livestock fodder (after processing to reduce its spines), and for erosion control and fuelwood. In Hawaiʻi, it was introduced as a hedge plant and has since become naturalized in upland pastures, roadsides, and disturbed areas at elevations of approximately 760–2,000 meters or higher on Molokaʻi, Maui, and Hawaiʻi Island. It was first collected on Maui in 1910.

Risks & Threats
Ulex europaeus is naturalized in Hawaiʻi and possesses traits that are cause for concern. It forms dense, nearly impenetrable thickets that crowd out native vegetation, reduce biodiversity, hinder livestock movement, and interfere with land management. The species produces abundant long-lived seeds that can remain viable in the soil for decades, allowing populations to recover quickly after disturbance. Its highly flammable foliage and dense growth can also increase wildfire frequency and intensity, creating conditions that further favor its spread while damaging native ecosystems. Because gorse is already widespread in parts of Hawaiʻi, planting or intentionally spreading it should be avoided, particularly in areas where it is not yet well established. Landowners are encouraged to manage existing populations and choose low-risk or native alternatives for hedges, screening, or erosion control whenever suitable options are available.

High Risk Traits:

• Wide climate adaptability – Grows in tropical montane regions and temperate zones; tolerates a broad elevation range (460–3,200 m).
  
• History of invasiveness – Naturalized and a serious pest in Hawaii, Sri Lanka, La Réunion, South America, and New Zealand.
  
• Naturalized on multiple Hawaiian Islands – Established and invasive on Molokai, Maui, and Hawaiʻi
  
• Dense thicket formation – Creates impenetrable, monotypic stands that outcompete native vegetation.
  
• Spiny/mechanical defenses – Produces spines, reducing accessibility and deterring some herbivores.
  
• Fire hazard – High combustible biomass; regenerates and germinates vigorously after fire.
  
• Toxic to humans – Branches and fruits are poisonous if ingested.
  
• Effective dispersal – Explosive pod dehiscence, water dispersal, ant dispersal, and human/soil movement.
  
• Large, persistent seed bank – Produces up to 10,000–20,000 seeds/m²; seeds remain viable in soil for 30+ years.
  
• Resprouting ability – Coppices after cutting; fire stimulates seedling germination.
  
• Nitrogen-fixing – Allows growth in nutrient-poor soils.
  
• Weedy in agricultural/disturbed areas – Invades pastures, grazing lands, roadsides, and logged areas.

Low Risk Traits:

• Palatable to grazing animals – Goats and sheep can effectively browse it, aiding control
  
• Not toxic to animals – Safe for livestock grazing
  
• Limited shade tolerance – Prefers full sun; dies back under heavy shade
  
• Requires insect pollination – Not self-pollinating; seed production drops to zero without pollinators