Guinea grass is a giant African grass introduced to the Hawaiian Islands sometime before 1871. This is one of the widest used forage grasses in the tropics and has been introduced everywhere cattle are raised. This grass is one of the most serious weeds we contend with at Nā Pōhaku o Hauwahine. Wherever established, the grass shades out and kills any smaller plants.

Guinea grass is widespread across O‘ahu and recognized by its size and the itching to the skin produced by close contact with the stems. Many in Hawai‘i want to call this "California grass", which is incorrect. California grass (Urochloa mutica) is a different large grass typically associated with wet areas (Kawai Nui marsh, for example). California grass has the long hairs on the stem like Guinea grass, but these do not come off and get into the skin. Further, California grass is characterized by very long, creeping stems and not the dense bunchy growth of Guinea grass.