Edition 1 (1937) of this work listed just over 2000 species. A preliminary survey for this revision showed a three-fold increase of species for inclusion and an overall increase of information available for those in Edition 1. Families are being dealt with alphabetically, and genera within families, and species within genera also alphabetically. Herewith, volume 4 with families M to R has some 1100 species including the all-important Gramineae. European and trade-names, if known, are given for each species. There follow a brief description, the sort of habitat each frequents, and then the known economic attributes in West Africa, and over the rest of Africa and beyond, if so wide-spread.