Family: Oleaceae

Origin, Description & Uses
Olea europaea subsp. europaea is a long-lived evergreen tree native to the Mediterranean region, where it has been cultivated for thousands of years. It is best known for producing edible olives and high-quality olive oil, and it is also widely grown as an ornamental and agricultural tree in warm, dry climates around the world. The tree typically has a gnarled trunk, narrow silvery-green leaves, and a slow-growing, drought-tolerant form that makes it well suited to arid landscapes and managed orchards.

Risks & Threats
In Hawaiʻi, this species is now naturalized on Maui and the Island of Hawaiʻi. Although valued for its cultural, culinary, and landscaping uses, it does possess traits that are cause for concern, including its ability to tolerate dry conditions and establish outside of cultivation. These characteristics may allow it to persist and potentially spread in certain habitats, where it could compete with native vegetation and contribute to long-term ecological change. Ongoing assessment is needed to better understand its behavior in Hawaiian ecosystems, and caution is recommended to ensure it does not negatively impact Hawaiʻi’s unique native environments. Choosing low-risk or native alternatives is encouraged where appropriate.

High Risk Traits:

• Highly domesticated but naturalizes readily
  
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• Naturalized beyond native range (Australia, Hawaii, South Africa)
  
• Documented environmental weed
  
• Naturalized in tropical/subtropical climates (high elevations in Hawaii)
  
• History of repeated introductions outside native range
  
• Forms dense thickets that suppress native plants
  
• Tolerates wide range of soils (including poor and calcareous soils)
  
• Produces viable seed (especially after bird/animal ingestion)
  
• Self-compatible (partial self-fertility)
  
• Reproduces vegetatively (resprouts after cutting or fire)
  
• Propagules dispersed intentionally by people (commercial and ornamental)
  
• Propagules bird-dispersed (many bird species)
  
• Propagules survive gut passage (birds, foxes, deer, goats, sheep)
  
• Persistent seed bank (2–3 years soil viability)
  
• Tolerates mutilation, cultivation, and fire (vigorous resprouting)
  
• Causes hayfever (pollen allergen)
  
• Creates fire hazard (highly flammable, increases fuel load)

Low Risk Traits:

• Requires cool nights to flower/fruit; limited in warm lowland tropics
  
• No spines, thorns, or burrs
  
• Not parasitic, toxic to animals, or unpalatable to grazers
  
• Not a prolific seed producer (<1000/m²)
  
• No wind, water, or external animal dispersal (drupes too large, no hooks)
  
• Propagules unlikely to contaminate produce (large fruits)