Family: Myrtaceae

An invasive tree that spreads from initial plantings to form dense thickets. Syzygium jambos, commonly called rose apple, has been cultivated so long the native range is obscure. The best guess at its origins is the East Indies and Malaysia. Widely introduced throughout the tropics, rose apple has naturalized almost everywhere it was introduced. It was imported to Hawai’i in 1825 aboard the HMS blonde. Today it is naturalized on all the main Hawaiian Islands.

The tree is self-fertile and reaches reproductive maturity in 5 years. It drops a lot of fruit, which makes an excellent habitat for fruit flies and gnats. Pigs rut up the ground while feasting on the fallen fruit. The rutted areas collect rainwater, which in turn makes habitat for mosquitoes. The understory of a rose apple forest is a dark place full of bugs. It grows into monospecific stands outcompeting other desirable species. The shade-tolerant tree can survive and thrive in the dark.

In 2005 a rust called Austropuccinia psidii was detected. Ohia and other members of the myrtle family were affected. Rose apple got it the worst. This rust attacks new growth deforming and discoloring leaves. In wet areas, where the rust is worse, whole stands are bare of leaves and fruit. The rust is less severe in dry areas.

Description and Dispersal:

• A small tree with low branches
  
• White showy stamens look similar to ohia
  
• Yellowish fruit with a crispy texture
  
• Fruit is hollow inside except for the round brown seed
  
• Fruit smells like a rose
  
• Seeds are dispersed by water, pigs, birds and humans
  
• Reproduces by vegetative fragments

High Risk Traits:

• Widespread naturalization and repeated introductions outside native range
  
• Naturalized on Kaua'i, O'ahu, Moloka'i, Lāna'i, Maui, and Hawai'i
  
• Forms dense, monospecific thickets that shade out native vegetation
  
• Recognized as an environmental, agricultural, and forestry weed
  
• Congeneric species (S. cumini) is invasive
  
• Highly adaptable: shade tolerant and grows across a wide range of soil types and elevations
  
• Reproduces both by viable seeds (self-compatible) and vegetative fragmentation
  
• Multiple dispersal pathways: water, birds, intentional human planting, and accidental transport
  
• Propagules survive passage through animal guts
  
• Resprouts vigorously after damage or pruning
  
• Exhibits allelopathic properties
  
• Host for the rust pathogen Austropuccinia psidii

Low Risk Traits:

• No spines, thorns, or burrs
  
• No evidence of toxicity to humans or animals; palatable to grazers
  
• Not wind-dispersed and not a contaminant of produce
  
• Not highly prolific seed producer
  
• Responds well to herbicide control