Molecular phylogeny and taxonomic reassessment of the genus Cladostephus (Sphacelariales, Phaeophyceae)

The brown algal genus Cladostephus (Sphacelariales) is found worldwide in temperate regions. Two species are considered endemic to South America (C. antarcticus Kützing and C. hariotii Sauvageau), whilst specimens from the rest of the world are usually attributed to a third, cosmopolitan species, C. spongiosus (Hudson) C.Agardh. However, comparisons of organellar (plastid rbcL and psbC, mitochondrial COI-5P) and nuclear (ITS nrDNA) markers for samples collected throughout the geographic range of C. spongiosus suggest that two genetic entities are treated under this name, which correspond to previously recognized morphological entities. Specimens with ‘spongiose’ morphology (C. spongiosus s.s.) were found to be limited to the Atlantic coast of Western Europe. The entity showing ‘verticillate’ morphology (‘C. verticillatus’) emerged as the cosmopolitan species: specimens were found on the Atlantic coasts of western Europe and the USA, in the Mediterranean, in New Zealand, Australia and on the Pacific coast of Mexico. Since the name C. verticillatus (Lightfoot) Lyngbye is illegitimate, this entity is herein referred to as C. hirsutus (L.) Boudouresque & M.Perret. A third genetic entity was only encountered in the southern hemisphere, i.e. in New Zealand, Australia, southern Chile and Falkland Islands. Comparisons with descriptions and images of type specimens suggest that this southern entity conforms most closely to the description of Cladostephus australis Kützing, nom. illeg., and it is herein renamed as Cladostephus kuetzingii Heesch, Rindi & W.A.Nelson.