Multigene phylogenetic analyses support recognition of the Sporolithales ord. nov.
Abstract
Recently, Le Gall and Saunders (2007) published a supraordinal phylogeny of the Florideophyceae that revealed a strong alliance between the Corallinales and Rhodogorgonales resulting in these orders being assigned to a new subclass, the Corallinophycidae. The Corallinales and Rhodogorgonales are unique among marine red algae for the presence of calcite (Borowitzka, 1977; Norris and Bucher, 1989) and they share pit plugs with domed outer caps (although not unique to these two taxa; Pueschel, 1989). Currently, the Corallinales includes three families: the Corallinaceae, Hapalidiaceae and Sporolithaceae (Harvey et al., 2003). Unfortunately, Le Gall and Saunders (2007) did not include in their analyses representatives of the Sporolithaceae, a family for which the taxonomic placement has been an ongoing debate. Sporolithon, proposed by Heydrich (1897), was either placed in its own tribe within the Melobesioideae (Johansen, 1969), or in its own subfamily within the Corallinaceae (Cabioch, 1972), and then elevated to familial rank based on distinctive features of tetrasporangial development (cruciately arranged tetrasporangia and absence of tetrasporangial conceptacles; Verheij, 1993). Townsend et al. (1994) expanded this family with a second genus, Heydrichia, and currently the Sporolithaceae contains 17 species (Guiry and Guiry, 2008).