The Grateloupia-complex in the red algal order Halymeniales contains ca. 116 species placed in seven genera. Most were originally placed in Grateloupia C. Agardh, one of the largest genera within the Rhodophyta. However, the current classification remains controversial. Recent studies that combined DNA sequence analyses (including chloroplast phylogenomics), and data on pre- and post-fertilization development provide substantial clues for resolving the intergeneric relationships of this complex. In particular, the architecture of the auxiliary cell ampullae (= the female reproductive structure that will receive the diploid nucleus resulting from karyogamy and gives rise to the carposporophyte generation) and its behavior before and after diploidization are critical for delimiting genera. In this presentation, we re-examine the generic concepts of Phyllymenia J.Agardh, Prionitis J.Agardh, Dermocorynus P.Crouan & H.Crouan, and Mariaramirezia M.S.Calderon, G.H.Boo, A.Mansilla & S.M.Boo and highlight critical pre- and post-diploidization stages in order to resolve the systematics of the Halymeniales, based on a selection of representative species.