The circumscription of genera within the family Rubiaceae is by no means a precise endeavor at the current time. For example, the genus Relbunium (Endl.) Hook. f. is currently included as a section of Galium L., sensu Dempster, although this placement does not have unanimous support among specialists. To clarify these uncertainties, this study examined whether Relbunium is an autonomous genus or a section of Galium by analyzing the morphology and development of flowers and fruits of the following species: G. latoramosum Clos, G. uruguayense Bacigalupo, R. equisetoides (Cham. & Schltdl.) Ehrend., R. gracillimum Ehrend., R. hirtum (Lam.) K. Schum., R. humile (Cham. & Schltdl.) K. Schum., R. humilioides M. L. Porto & Ehrend., R. hypocarpium (L.) Hemsl., R. longipedunculatum Mariath & Ehrend., R. mazocarpum Greenm., R. megapotamicum (Spreng.) Ehrend., R. nigro-ramosum Ehrend., R. ostenianum Standl., R. richardianum (Gillies ex Hook. & Arn.) Hicken, and R. valantioides (Cham. & Schltdl.) K. Schum. This morphological data set and analysis were then used to construct a cladogram, which indicates that Galium is a sister group to Relbunium and further characterizes Relbunium as a monophyletic clade that should be considered an autonomous genus.