A revised classification of the Sphacelariales (Phaeophyceae) inferred from a psbC and rbcL based phylogeny

Phylogenetic relationships within the brown algal order Sphacelariales and with its sister group were investigated using chloroplast-encoded psbC and rbcL DNA sequences. A pilot study with 21 non-sphacelarialeans, representing nine orders (and some incertae sedis taxa), showed a strongly supported monophyly of the Sphacelariales with its sister taxa Phaeostrophion irregulare, Bodanella lauterborni and Heribaudiella fluviatilis. These three taxa were selected as outgroup for further analyses including DNA sequences of 30 sphacelarialean specimens representing all but two of the recognized genera (Phloiocaulon and Ptilopogon were not sampled). Bayesian Inference and Maximum Likelihood trees showed some incongruence with Maximum Parsimony trees. Trees based on rbcL showed some incongruence with trees based on psbC and combined alignments. Phylogenetic results were used as the basis for a newly proposed classification of the Sphacelariales that reflects evolutionary history. The Sphacelariales is subdivided into four families: Cladostephaceae (monotypic), Sphacelariaceae, Stypocaulaceae, and a newly created monotypic family Sphacelodermaceae to incorporate Sphaceloderma caespitula, comb. nov. (former Sphacelaria caespitula). Sphacelaria radicans is transferred to a newly created genus Protohalopteris and classified in the Stypocaulaceae, which also contains the two unsampled genera Phloiocaulon and Ptilopogon as well as the genus Halopteris. The genera Stypocaulon and monotypic Alethocladus were merged with Halopteris. The Sphacelariaceae were subdivided into six genera including Sphacelaria (consisting only of the former subgenus Propagulifera) and the monotypic Sphacella. Herpodiscus durvillaeae, Sphacelaria pulvinata and the Sphacelaria subgenera Bracteata and Reinkea were merged in an emended Herpodiscus. A new genus Sphacelorbus was created for Sphacelaria nana. Battersia was reinstated for Sphacelaria mirabilis and the subgenus Pseudochaetopteris, except for Sphacelaria plumosa for which Chaetopteris was reinstated.