Gramineae or Poaceae constitute the largest family of higher plants and are truly cosmopolitan, occupying c. 20% of the emersed lands. Their importance as food is enormous including all cereals, from wheat, barley, oats to rice. Africa's tropical and subtropical savannas are extensive and extremely important ecosystems, consisting of grasses and spaced out trees that act as a refuge for an extraordinary variety of animals.
Guinea-Bissau is a small tropical country (2.5 times smaller than Portugal) more than 20% of its territory being occupied by water. Mangroves thrive along the coast and river banks. There are also areas of rice paddies, sub-humid and dry forests, and inland savannas. Here, grasses play an important role. Those grasses that develop in the salty areas, with soil saturated with salt, where few species can survive, are also of major ecological importance.