Family: Myrtaceae

A fast-growing tree that forms thick strands. Native to Australia, New Caledonia, and New Guinea, Melaleuca quinquenervia, commonly known as paperbark, thrives in swampy areas. Listed as a federal noxious weed, thousands of acres have been invaded in Florida to the detriment of native plants. Besides that, the pollen produced from paperbark causes ½ to 2 million dollars a year in allergy treatments for Floridians. In Hawaiʻi, paperbark has naturalized on all the main islands. Propagule pressure is substantial due to the 1.7 million trees that were planted. This species is flammable and grows back fast after a fire disturbance.

Furthermore, paperbark is allelopathic. Chemicals released by this species inhibit the germination and growth of other species. The Division of Forestry and Wildlife of the Hawaiʻi Department of Land and Natural Resources has designated this species as one of Hawaiʻi’s Most Invasive Horticultural Plants.

Description and Dispersal:

• A tall tree up to 75 ft with thick, spongy, tan bark that peels in papery layers
  
• Narrow leaves (3.5 in long by 0.6 in wide) with 3-5 prominent veins grow in an alternate pattern
  
• Flowers are cream colored and grow in 'bottlebrush' spikes; small woody fruits are button-like seed capsules
  
• Seeds are dispersed by wind and water, large numbers of seeds are stored in the tree and released after a disturbance occurs

High Risk Traits:

• Naturalized and a serious environmental weed in Florida
  
• Tolerates broad range of climates (tropical to warm temperate)
  
• Allelopathic (inhibits other plant germination)
  
• Unpalatable to grazing animals
  
• Causes allergies/respiratory problems in humans
  
• Creates fire hazard (flammable bark)
  
• Forms dense thickets (up to 20,000 stems/ha)
  
• Tolerates wide range of soil conditions (including saline, infertile, waterlogged)
  
• Produces abundant, wind- and water-dispersed seeds (~2.7 million viable seeds/kg)
  
• Reproduces by seed starting at 3 years old
  
• Tolerates fire and coppices readily
  
• Dispersed intentionally by people and along roadsides

Low Risk Traits:

• No spines, thorns, or burrs
  
• No evidence of toxicity to animals
  
• Not shade tolerant (requires full sun to partial shade)
  
• Obligate outcrosser (not self-compatible)
  
• No vegetative fragmentation via root suckers
  
• No persistent soil seed bank (seeds held in canopy)
  
• Controllable with herbicides