Phylogeny of the Bangiophycidae (Rhodophyta) and the secondary endosymbiotic origin of algal plastids

The Rhodophyta (red algae) are composed of the subclasses Bangiophycidae an d Florideophyreidae. Two evolutionarily interesting features of the Bangiop hycidae are: (1) they are the ancestral pool from which the more morphologi cally complex taxa in the Florideophycidae have arisen and (2) they are the sources of the plastids, through secondary endosymbioses, for the Cryptoph yta. Haptophyta. and the Heterokonta. To understand Bangiophycidae phylogen y and to gain further insights into red algal secondary endosymbioses, we s equenced the plastid-encoded small subunit ribosomal DNA (rDNA) coding regi on from nine members of this subclass and from two members of the Florideop hycidae. These sequences were included in phylogenetic analyses with all av ailable red algal plus chlorophyll rr + c algal plastid rDNA coding regions . Our results are consistent with a monophyletic origin of the Florideophyc idae with these taxa forming a sister group of the Bangiales. The Bangiophy cidae is of a paraphyletic origin with orders such as the Porphyridiales po lyphyletic and distributed over three independent red algal lineages. The p lastids of the heterokonts are most closely related to members of the Cyani dium-Galdiera group of Porphyridiales and are not directly related to crypt ophyte and haptophyte plastids. The phylogenies provide strong evidence for the independent origins of these "complex" algal plastids from different m embers of the Bangiophycidae.