The fourth and final volume of the Flora of Oman deals with the monocotyledonous families (21 families and 246 taxa) It follows Cronquist’s (1981) system, with notes where APG IV (2016) or recent molecular evidence treats the families or genera differently. It contains the Poaceae, represented by 172 taxa. The keys and species descriptions are accompanied with notes on conservation status and distribution maps are for all described species.