Ribosomal DNA phylogeny of the Bangiophycidae (Rhodophyta) and the origin of secondary plastids

We sequenced the nuclear small subunit ribosomal DNA coding region from 20 members of the Bangiophycidae and from two members of the Florideophycidae to gain insights into red algal evolution. A combined alignment of nuclear and plastid small subunit rDNA and a data set of Rubisco protein sequences were also studied to complement the understanding of bangiophyte phylogeny and to address red algal secondary symbiosis. Our results are consistent wi th a monophyletic origin of the Florideophycidae, which form a sister-group to the Bangiales. Bangiales monophyly is strongly supported, although Porp hyra is polyphyletic within Bangia. Bangiophycidae orders such as the Porph yridiales are distributed over three independent red algal lineages. The Co mpsopogonales sensu stricto, consisting of two freshwater families, Compsop ogonaceae and Boldiaceae, forms a well-supported monophyletic grouping, The single taxon within the Rhodochaetales, Rhodochaete parvula, is positioned within a Cluster containing members of the Erythropeltidales. Analyses of Rubisco sequences show that the plastids of the heterokonts are most closel y related to members of the Cyanidiales and are not directly related to cry ptophyte and haptophyte plastid genomes. Our results support the independen t origins of these secondary algal plastids from different members of the B angiophycidae.