Nuclear 18S rRNA gene sequence analyses indicate that the Mastophoroideae (Corallinaceae, Rhodophyta) is a polyphyletic taxon

Nuclear small subunit ribosomal RNA (18S rRNA) gene sequences were determined for six species representing three genera classified within the Mastophoroideae, and also for two species of Amphiroa (Lithophylloideae). These data were combined with previously published 18S rRNA sequences for 38 other coralline species and analysed (1) to determine the phylogenetic position of the Mastophoroideae within the Corallinaceae and (2) to examine relationships among Hydrolithon, Metamastophora, Neogoniolithon and Spongites. Trees derived from parsimony and maximum likelihood analyses of these data indicate that the Mastophoroideae is not monophyletic. Instead, our data suggest that the group is polyphyletic and includes species belonging to four distinct evolutionary lineages. For example, Neogoniolithon spp. were associated with geniculate members of the Corallinoideae, and Hydrolithon was resolved as sister to the geniculate genus Metagoniolithon. We demonstrate that each of the four 'mastophoroid' lineages share a number of vegetative and reproductive features with their respective sister taxa. Together the molecular and morphological data imply that the Mastophoroideae is not monophyletic and that genera placed in this taxon might more naturally be classified in other subfamilies. Also, on the basis of our findings, Porolithon pachydermum is transferred to Hydrolithon as H. pachydermum (Foslie) Bailey, Gabel Freshwater.