Affiliation of the parasite Herpodiscus durvillaeae (Phaeophyceae) with the Sphacelariales based on DNA sequence comparisons and morphological observations

The phylogenetic affinities of the brown alga Herpodiscus durvillaeae, an obligate parasite of Durvillaea antarctica (Fucales, Phaeophyceae) endemic to New Zealand, were analysed using combined partial nuclear encoded ribosomal DNA (26S) and plastid encoded RuBisCO (rbcL) gene sequences. Results from phylogenetic analyses place this species within the order Sphacelariales. Molecular data were supported by two morphological features characteristic for the Sphacelariales sensu stricto: the presence of apical cells and the transitory blackening of the cell wall with sodium hypochlorite solution ('Eau de Javel'). However, the strongly heteromorphic life history distinguishes H. durvillaeae from all other members of the Sphacelariales of which the life cycle is known. This variability in life history provides a new systematic character for the order and should be taken into account in any comprehensive systematic revision of the Sphacelariales.