Family: Cannabaceae

Origin, Description & Uses
Humulus lupulus, commonly known as common hop or European hop, is a fast-growing, perennial climbing vine native to Europe, western Asia, and parts of North America. It is characterized by rough, twining stems, lobed leaves, and distinctive cone-like flowers (called “hops”) produced by female plants. These cones are widely used in brewing to add bitterness, aroma, and stability to beer, making hops an economically important crop worldwide. In addition to its primary role in the brewing industry, hops have also been used in traditional herbal medicine and occasionally as an ornamental vine for trellises and fences.

Risks & Threats
Although Humulus lupulus is not currently known to be naturalized in the Hawaiian Islands, it possesses traits that raise concern for tropical ecosystems. Its vigorous growth, climbing habit, and ability to spread through both seeds and underground rhizomes could allow it to outcompete native vegetation, especially in disturbed or mesic environments. Dense growth may smother surrounding plants and alter habitat structure. Because of its economic importance as a specialty crop, limited cultivation may be appropriate; however, it should be managed carefully to prevent unintentional escape or spread. Monitoring and containment practices are recommended to reduce the risk of this species becoming invasive and negatively impacting Hawaii’s unique ecosystems.

High Risk Traits:

• Broad climate suitability
  
• Widely cultivated and naturalized in temperate areas (but no evidence in Hawaiian Islands to date)
  
• A yard, garden and general weed of cultivated lands
  
• Potential agricultural and environmental weed (impacts unverified0
  
• Humulus japonicus is invasive
  
• Toxic to dogs
  
• May cause dermatitis to susceptible individuals
  
• Tolerates many soil types
  
• Climbing and potential smother habit
  
• Reproduces by seeds and vegetative fragments
  
• Seeds dispersed by wind, water, animals and intentionally by people
  
• Vegetative fragments dispersed by machinery
  
• Seeds persist for >1 year (possibly 3 years)
  
• Tolerates cutting and freezing (regrows from roots)

Low Risk Traits:

• Primarily grows in temperate climates (may limit ability to persist and spread to higher elevation areas of tropical islands)
  
• Unarmed (no spines, thorns, or burrs)
  
• Provides fodder for livestock (palatable to some grazing animals despite toxicity to dogs)
  
• Integral ingredient in beer brewing
  
• Dioecious (female flowers used in brewing; eliminates seed production if no male plants are present)
  
• Herbicides may provide effective control