Family: Fabaceae

Origin, Description & Uses
Vachellia farnesiana, commonly known as klu or sweet acacia, is a thorny shrub or small tree native to tropical and subtropical regions of the Americas. It is recognized by its finely divided, feathery leaves, sharp paired thorns, fragrant golden-yellow puffball flowers, and dark seed pods. Sweet acacia has long been cultivated as an ornamental and for its highly fragrant flowers, which have been used in perfume production. In Hawaiʻi, it was once grown in an attempt to establish a perfume industry but has since escaped cultivation. It is now naturalized on all of the main Hawaiian Islands and Kuaihelani (Midway Atoll), where it commonly grows in dry, open, and disturbed habitats.

Risks & Threats
Vachellia farnesiana is naturalized in Hawaiʻi and possesses traits that are cause for concern because it can spread into dry grasslands, shrublands, pastures, roadsides, and other disturbed areas, where it forms dense, thorny stands that can displace desirable vegetation and hinder access for people and wildlife. It produces abundant long-lived seeds that are readily dispersed by animals and water, allowing populations to expand and persist after disturbance. Its ability to tolerate drought, poor soils, and repeated disturbance makes it especially successful in tropical island environments. Because this species is already widespread in Hawaiʻi and could continue to negatively impact tropical island ecosystems, it should be managed where possible and its use should be avoided in areas where it is not yet widely established. When selecting plants for landscaping or restoration, choose low-risk or native alternatives whenever suitable options are available.

High Risk Traits:

• Broad climate and soil tolerance (tropical/subtropical, poor/sandy soils)
  
• Naturalized and weedy in many regions (Australia, USA, Pacific Islands)
  
• Naturalized across the Hawaiian Islands: Kuaihelani (Midway Atoll), Kaua'i, O'ahu, Moloka'i, Lāna'i, Kaho'olawe, Maui, and Hawai'i
  
• Forms dense, impenetrable thorny thickets
  
• Creates fire hazard in dry habitats
  
• Dispersed intentionally by people (ornamental/forestry) and by ungulates eating pods
  
• Persistent seed bank (hard seed coat dormancy)
  
• Regenerates from basal shoots after fire
  
• Reaches reproductive age in ~3 years
  
• Host to pests and fungal pathogens
  
• Congeneric species are known weeds

Low Risk Traits:

• Not toxic to animals or humans
  
• Palatable to livestock (though spines limit access)
  
• No vegetative reproduction
  
• No wind, external animal, or contaminant seed dispersal
  
• Not shade-tolerant
  
• Controllable with herbicides (glyphosate, tebuthiuron, picloram)