A synoptic key for identifying the Gigartinales, Halymeniales, Hildenbrandiales and Plocamiales from the Western Mediterranean has been prepared in order to facilitate the recognition of these res algae. The orders Gigartinales with some 69 species grouped in 19 families and 35 genera, Halymeniales, with 13 species grouped in 2 families and 6 genera, Hildenbrandiales with 1 family and 1 genera of 3 species, and Plocamiales, with 1 family and 1 genus of 2 species are included. The genus Wudermannia Harvey is also included in the key, althought it has not finally been established whether it belongs to the order Gigartinales or not. Morphological and anatomical descriptions of the reproductive structures, using data from the literature and from personal observations are presented