Phalaris L. (Poaceae, canary grasses) is a genus of 20 species found throughout the world with endemic, cosmopolitan, invasive and forage species. A variety of features in the genus underscore its importance for the study of polyploid evolution in relation to biodiversity, ecological niche expansion or contraction, endemism, and invasiveness. A formal and comprehensive infrageneric classification for Phalaris is lacking. This study utilises molecular phylogenetics (nuclear ITS and plastid trnT–F regions), morphological features (primarily floret structure) and chromosome cytology to present the first comprehensive taxonomic classification for the genus. Two subgenera (Phalaris and Phalaroides) and five sections (Phalaris, Phalaroides, Caroliniana, Bulbophalaris, Heterachne) are established here to accommodate the 20 Phalaris species. Keys to the subgenera and sections, morphological descriptions, and a list of synonymy are provided.