A cladistic analysis of Rhodophyta: Florideophycidean orders

Abstract

A cladistic analysis of the orders of red algae is presented that concentrates on relationships among florideophyte taxa. The data matrix comprises 35 characters and 15 taxa. Biochemical and ultrastructural characters as well as features of vegetative and reproductive morphology and life history were used. Based on a previous cladistic analysis, Erythropeltidales are used as the outgroup to polarize characters among florideophyte orders. Batrachospermales, Ceramiales, Corallinales, Gelidiales, Hildenbrandiales and Nemaliales appear monophyletic, as do Palmariales with the possible exception of one or two genera. Recognition of Acrochaetiales and Bonnemaisoniales is supported, even though the former may be paraphyletic and the latter polyphyletic based on the inclusion of Naccariaceae. Gigartinales appear to be paraphyletic, and relationships among the constituent families need to be resolved to determine the status of the order. Rhodymeniales may not merit ordinal recognition as all of the synapomorphies and autoapomorphies that distinguish this taxon are also found in some taxa in Gigartinales, with the exception of tetrahedrally divided tetrasporangia. Relationships among syntagmatic taxa with two-layered plug caps are unresolved as is the relationship of these taxa with the zero-layered plug-cap lineage.