XVI International Botanical Congess

Division Rhodophyta is regarded as monophyletic. Although unique synapomorphies are lacking, a suite of ultrastructural and biochemical characters distinguishes the red algae from other groups. Extensive 18S nr DNA analyses resolve poorly the evolutionary origin of, and the sister groups to, red algae, because they and other >crown= eukaryote groups diverged nearly simultaneously. Amino acid sequences of conserved nuclear and mitochondrial protein-coding genes may provide more resolution. Subclass Bangiophycidae is paraphyletic due to the evolutionary diversity of unicellular genera presently placed in the Porphyridiales. Some simple algae now in the Bangiophycidae (e.g. Dixoniella, Glaucosphaera) may instead be basal within subclass Florideophycidae. Nucleomorphs of cryptomonads and chlorachniophytes should also be regarded as red algae.