Family: Zygophyllaceae

Origin, Description & Uses
Guaiacum sanctum, commonly known as holywood or lignum-vitae, is a slow-growing, evergreen tree native to tropical regions of the Caribbean, Central America, and northern South America. It is well known for its extremely dense, durable wood—among the hardest and heaviest of any tree—which has historically been used for shipbuilding, tools, carvings, and specialty items requiring high wear resistance. The tree typically has a rounded canopy, dark green compound leaves, and produces attractive blue to purple flowers followed by small orange-yellow fruits. Due to its ornamental value and unique wood properties, it has been cultivated in tropical landscapes, including in Hawai‘i.

Risks & Threats
Guaiacum sanctum is naturalized on Oʻahu and does possess traits that are cause for concern. While it is generally slow-growing, it can establish in suitable habitats and persist over time, potentially competing with native vegetation. Its tolerance of dry, coastal, and lowland environments may allow it to spread in sensitive ecosystems. Although significant negative impacts have not been widely documented in Hawai‘i, caution is recommended to ensure that this species does not expand further or negatively affect native plant communities. Continued monitoring and evaluation are advised to better understand its long-term ecological effects.

High Risk Traits:

• Naturalizing in Koko Crater, Oahu, Hawaiian Islands
  
• Native to and thrives in tropical climates
  
• Shade-tolerant (could establish in intact forest understory)
  
• Tolerates many soil conditions (and potentially able to exploit many different habitat types)
  
• Viable seeds dispersed by birds and possibly small mammals
  
• Self-compatible
  
• Able to resprout after cutting or damage from hurricanes, and possibly fire

Low Risk Traits:

• No records on naturalization or invasiveness reported elsewhere in the world
  
• Unarmed (no spines, thorns or burrs)
  
• Non-toxic (but medicinal properties to caution is advised)
  
• Ornamental value
  
• Timber tree
  
• Slow growth rate and long time (30+ years) to reproductive maturity
  
• No evidence of spread by vegetative means