Family: Urticaceae

Origin, Description & Uses
Urtica urens (burning nettle, dwarf nettle, or lesser stinging nettle) is an annual herb native to Europe, parts of Asia extending to Siberia and the Himalayas, and portions of northern and northeastern tropical Africa and the Arabian Peninsula. It has since spread throughout much of the world and is now considered a nearly cosmopolitan weed. In Hawaiʻi, it was first collected in 1909 and is naturalized on Oʻahu and Hawaiʻi Island, where it occurs in pastures and subalpine forests at elevations of approximately 790–2,290 m (2,600–7,500 ft). The plant is recognized by its small green flowers and leaves covered with stinging hairs that can cause a painful skin irritation. Although it has been used in traditional herbal medicine and as a leafy vegetable after careful preparation to neutralize the stinging hairs, it is more commonly regarded as a troublesome weed.

Risks & Threats
Urtica urens is naturalized in the Hawaiian Islands and possesses traits that are cause for concern. It produces abundant seed, readily colonizes disturbed sites, agricultural lands, pastures, roadsides, and natural habitats, and can form dense populations that compete with other vegetation. Its painful stinging hairs discourage people and animals from entering infested areas, reducing access for recreation, agriculture, and land management. While it is already established in parts of Hawaiʻi, preventing its spread into uninfested areas and minimizing further expansion can help protect native ecosystems and reduce management costs. Where practical, avoid planting or intentionally spreading this species, and choose a low-risk or native alternative for landscaping or restoration projects. In areas where burning nettle is already widespread, focus on managing existing populations and preventing its introduction into new locations, particularly near sensitive native habitats.

High Risk Traits:

• Elevation range exceeds 1000 m, demonstrating environmental versatility
  
• Naturalized in mid- to high elevation areas in the tropics
  
• Widely naturalized, including on Oahu and Hawaii island, Hawaii
  
• A disturbance adapted agricultural weed of numerous crops
  
• Other Utrica species have become invasive
  
• Stinging hair affect animals and humans
  
• Relatively unpalatable, although some animals may consume occasionally
  
• Reportedly flammable in certain habitats
  
• Tolerates many soil types
  
• Reported to form dense stands in certain crops
  
• Reproduces by seeds in one growing season (annual)
  
• Seeds dispersed in soil, as a contaminant, ingested by animals and intentionally by people
  
• Prolific seed production
  
• Forms a persistent seed bank (20-100 years)

Low Risk Traits:

• Due to predominantly temperate range, may only become invasive at higher elevations of tropical regions
  
• Despite stinging hairs, non-toxic if ingested by animals
  
• Used medicinally by people
  
• Require high light environments (may be Shade-intolerant)
  
• Reported to be outcrossing
  
• Not reported to spread vegetatively
  
• Seeds do not float in water
  
• Herbicides provide effective control