This paper reports a type study of those species and infraspecific taxa of "Lophodermium" described or reported from monocotyledons. The history of the taxonomy and classification of these fungi and methods used in their study are given, together with an outline of the morphology and ontogeny of the "Rhytismataceae" as a whole. The majority of the monocotyledon-inhabiting species can be placed in one of five broad morphological groups. The morphology and ontogeny of these groups are described in detail, together with notes on those morphological characters most useful at both the specific and supraspecific level. The biology and geographical distribution of the monocotyledon-inhabiting species is discussed. A cladistic analysis compares the relationships of the groups recognized among the monocotyledon-inhabiting species with "Rhytismataceae" from other substrata. Keys are presented to all species.