Apomuria was described by Bremekamp as a segregate of Psychotria that is distinguished by seed and pyrene characters. Bremekamp noted that the genus includes species from East Africa, but he only formally named species from Madagascar (12 endemic species) and the Comores (1 otherwise East African species). These seed and pyrene characters are variable within clades of Psychotria, however, and Apomuria is clearly a heterogeneous assemblage. In particular Apomuria punctata and the other species with leaf nodules from East African nodulated group appear to be related to the African Psychotria subg. Tetramerae; Apomuria bullata appears to be related to the other Madagascar Psychotria species with bacterial leaf nodules; Apomuria moramangensis appears to be related to several Psychotria species of humid vegetation on the eastern escarpment of Madagascar; and the remaining Apomuria species may be mostly or all related to each other. Bremekamp distinguished the species of Apomuria mainly by leaf characters and details of pubescence, and several of them may not be distinct. He also recognized varieties of several Apomuria species, which were distinguished by details of the pubescence; in most cases the species are better documented and the pubescence variation seems to be continuous, however Apomuria angustifolia var. angustifolia and its var. pubescens may actually not be conspecific, and var. pubescens is similar to several other species of Apomuria but var. angustifolia may be more closely related to species now classified in Psychotria.
For more information about Apomuria including detailed outlines of the species and their putative relationships, see the genus page in the TROPICOS Rubiaceae Project (in the upper right corner of the web page, click on "Choose Project" and then "Rubiaceae"). Apomuria is similar in aspect to, and frequently confused with: Triainolepis, which differs in its ovaries with 2 ovules in each locule and subglobose multilocular fruits; Pyragra, which differs in its ovate, flattened, schizocarpous fruits with carpophores that persist after the mericarps have fallend; and some species of Cremocarpon, which has ellipsoid schizocarpous fruits that also have persistent carpophores. Also similar to some Apomuria species are several Psychotria species, which differ in their yellow corollas and fruits that become white then blue or black; particularly similar here are Psychotria boenyana, Psychotria ambongensis, and Psychotria rubropedicellata.