GUINEA GRASS (Megathyrsus maximus)

Synonym: Panicum maximum

Hawai‘i-Pacific Weed Risk Assessment Score: 17 (High Risk). Visit Plant Pono for moreGuinea grass inflorescence information. 

Weed Fire Risk Score = 0.89 (This species is likely a high fire risk in Hawai’i); Visit Pacific Fire Exchange Weed Risk Assessments  for more information

Regulatory Status: None

Prevention and Control Category: N/A


  • Shade tolerant perennial, grows in dense bunches, up to 9 ft tall, hairy or not, but densely hairy at nodes. Sheaths hairy or not except densely hairy at collar. Ligules very short fringed membrane. Leaves up to 3 ft long by 1 inch wide. Inflorescences open panicles, capable of producing 9000 seeds per plant. Germination rate is low unless the seeds are stored dry for 6 months or more. Seed produced asexually (apomictic), hence local populations tend to be genetically uniform.
  • Native to Africa, an important forage grass, widely introduced and naturalized throughout the tropics.


Guinea grass growing on Kahoʻolawe

  • Strong allelopathic activity.
  • Forms dense stands in unmanaged areas.
  • Increases fire risk in unmanaged or ungrazed landscapes, and during periods of drought.
  • Regenerates rapidly following fire, and can expand into burned areas.
  • Seeds dispersed by wind, and in animal droppings.


  • An important forage grass.


Naturalized and common, 0-850 m, on all of the main Hawaiian islands. Cultivated and probably found growing in the wild prior to 1871.

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