Family: Rhamnaceae

Alphitonia excelsa, commonly known as Cooper’s wood, red ash, soaptree, or whiteleaf, is a fast-growing tree native to New Guinea, New South Wales, Northern Territory, Queensland, and Western Australia. It is valued for its adaptability, ornamental appearance, and traditional uses, including soap-like qualities found in its leaves and bark. The tree produces clusters of small, fragrant white flowers followed by dark fruits that attract birds and other wildlife. Its silvery-green foliage and tolerance for a wide range of soils make it a popular choice in landscaping and reforestation projects in its native range.

In the Hawaiian Islands, Alphitonia excelsa is naturalized on O‘ahu, where it has spread beyond cultivation. Like many non-native trees, its ability to thrive in disturbed areas raises concerns about potential competition with native plants and disruption of local ecosystems. While it may offer some benefits, such as habitat for birds, its presence in natural landscapes should be monitored carefully to ensure it does not become more invasive or spread to additional islands.

High Risk Traits:

• Broad climate suitability, and elevation range exceeds 1000 m, demonstrating environmental versatility
  
• Grows in tropical climates
  
• Possibly naturalizing in Lyon Arboretum, Oahu, Hawaiian Islands
  
• Concerns raised in native range over potential to become a weed
  
• Other Alphitonia species may be invasive
  
• Tolerates many soil types
  
• Forms pure stands in native range
  
• Reproduces by seeds
  
• Reaches maturity in 1-2 years
  
• Seeds dispersed by birds and intentionally by people
  
• Seeds form a persistent seed bank (longevity unknown)
  
• Able to resprout after fires

Low Risk Traits:

• No reports of negative impacts
  
• Unarmed (no spines, thorns, or burrs)
  
• Provides fodder for livestock (palatable)
  
• Ornamental
  
• Shade-intolerant pioneer species
  
• Not reported to spread vegetatively
  
• Herbicides may provide effective control