Family: Malvaceae

Sida acuta (spinyhead sida, common wireweed) is a fast-growing shrub that thrives in tropical and subtropical climates. Originally from Central America, it has spread widely across the world and is now established in Hawai‘i. This species is highly adaptable, tolerating a broad range of soils and environments, and quickly forms dense thickets that crowd out native plants and pasture species. It produces abundant seeds that persist in the soil for years and spread easily on clothing, livestock, vehicles, and as contaminants in hay or seed. Self-pollination and rapid seed production ensure that populations can grow quickly once established.

As an invasive weed, Sida acuta is considered a serious agricultural and environmental threat. It competes aggressively with crops and pastures, reduces forage quality, and can host pests such as the cotton mealybug. Its dense stands can be difficult to remove, as the plant resprouts after cutting and tolerates heavy disturbance. Although effective herbicides are available, long-term control often requires persistent management to exhaust the seed bank. Preventing new introductions and controlling small populations early are the best ways to protect Hawai‘i’s landscapes and agriculture from this high-risk species.

High Risk Traits:

• Broad climate tolerance (tropical & subtropical; survives in varied soils).
  
• Naturalized and invasive across many regions worldwide, including Kaua'i, O'ahu, Maui, and Hawai'i.
  
• Agricultural, forestry, and horticultural weed.
  
• Forms dense thickets that outcompete other vegetation.
  
• Produces large amounts of viable seed (>1000/m²).
  
• Persistent seed bank (dormant seeds remain viable for years).
  
• Seeds spread widely:
  
• Cling to fur, wool, clothing, and vehicles.
  
• Survive gut passage in livestock.
  
• Spread as contaminants in produce/hay.
  
• Self-compatible (can self-pollinate, ensuring reproduction).
  
• Fast reproductive cycle (flowers and sets seed in 1 year).
  
• Tolerates grazing, cultivation, and cutting (can regrow).
  
• Hosts agricultural pests (e.g., cotton mealybug).
  
• Potentially allelopathic.
  
• Sometimes unpalatable or toxic to livestock.

Low Risk Traits:

• Does not produce spines, thorns, or burrs.
  
• No climbing/smothering growth habit (it’s erect/shrubby, not a vine).
  
• Not strongly shade-tolerant (seedlings especially suffer under shade).
  
• No specialist pollinator required (pollinated by a wide range of insects).
  
• Does not reproduce vegetatively (no root fragments, tubers, etc.).
  
• Can be controlled by herbicides if treated properly.
  
• Limited evidence of fire hazard (though dense stands may add fuel).
  
• No consistent evidence of toxicity to humans (used in traditional medicine in some regions, but not broadly harmful).