Abstract
Five phylogenetic schemes are presented for the Acrochaetiaceae based on comparative morphology and ultrastructure. The relationships between the possible phylogenetic relatives of the family and the taxonomic rank at which the group can be recognized are discussed. The most satisfactory schemes derive at least part of the Bangiophyceae from an acrochaetioid ancestor in which pit connections were present. All schemes that recognize the primitive nature of Audouinella in the Florideophyceae suggest the recognition of the Acrochaetiaceae at ordinal level. On this basis, the order Acrochaetiales is again proposed.