The conserved region of numerous MADS genes in gulfweed (Sargassum fulvellum) was cloned by PCR with degenerate primers. Analysis of seventy individual clones resulted in the identification of ninteen types of nucleotide sequences. There sequences encode portions of the MADS domain in four distinctive groups. Six clones belong to the AGAMOUS subfamily, ten to AGL2, and two to AGL12. The remaining one clone is distinctive and appears to be diverged from an ancestor of the AGL2 and AP1 groups. There were no A or B class MADS genes. These results suggest that, as found in land plants, MADS genes also play major roles in controlling the development of algae.