Family: Lygodiaceae

Origin, Description & Uses:
Japanese climbing fern (Lygodium japonicum) is native to tropical and subtropical regions of Asia and the western Pacific, including areas as far east as Palau. Unlike most ferns, this species has a distinctive twining growth habit, producing long, vine-like fronds that can climb over shrubs and trees. Its delicate, lacy foliage has made it a popular ornamental plant in some regions, particularly for trellises or naturalized garden settings. However, its ability to spread rapidly and climb aggressively sets it apart from more typical, ground-dwelling ferns.

Risks & Threats:
Japanese climbing fern is naturalized in Hawaiʻi (including Oʻahu and Hawaiʻi Island) and possesses several traits that raise concern. It grows quickly, reproduces by abundant wind-dispersed spores, and can form dense mats that smother native vegetation and alter forest structure. Its climbing habit allows it to overtop trees and shrubs, increasing shading and potentially contributing to fire risk by creating ladder fuels. These characteristics make it a serious threat to tropical island ecosystems, where native species may be outcompeted and ecosystem processes disrupted. Because of these risks, it is recommended to avoid planting this species and instead choose low-risk or native alternatives whenever possible.

High Risk Traits:

• Naturalized beyond native range (e.g., O'ahu, Hawai'i, southeastern US)
  
• Grows in sun or shade (shade tolerant)
  
• Climbing/smothering growth habit (forms dense mats, shades out vegetation)
  
• Reproduces by spores, rhizomes, and vegetative fragmentation
  
• Spores viable >1 year (persistent propagule bank)
  
• Wind-dispersed spores
  
• Self-compatible (high selfing rate, ~95%)
  
• Minimum generative time <1 year (fast growing)
  
• Tolerates mutilation/fire (resprouts from rhizomes)
  
• Creates fire hazard (dry fronds flammable)
  
• Agricultural weed (contaminates pine straw)
  
• Environmental weed (invades hammocks, riparian areas)
  
• Congeneric weed (L. microphyllum is invasive)

Low Risk Traits:

• No spines, thorns, or burrs
  
• No evidence of toxicity to animals or humans (though some sources note poison if ingested)
  
• Not dispersed by water, birds, or gut passage
  
• Well controlled by herbicides (e.g., glyphosate, triclopyr)