Studies of reproduction in Australian Dictyopteris australis and Dictyopteris muelleri (Dictyotales, Phaeophyceae) identify new taxonomic characters

Abstract

Detailed studies on the sporophytes and gametophytes of Dictyopteris australis and Dictyopteris muelleri from Australia have demonstrated the usefulness of several reproductive characters in species discrimination. In D. australis, spherical sporangia that project above the thallus surface and are clustered around reflexed bundles of paraphyses contrast markedly with the angular sporangia of D. muelleri, which are embedded in the thallus and are scattered in broad fertile zones on the upper branches. In D. muelleri, tetrads of released spores enveloped by the inner sporangial wall are temporarily retained above the thallus surface on the ends of mucilaginous stalks. Sporangial stalks have not been reported in any other species of the brown algae, although egg stalks are produced by several fucalean species. Differences in oogonial structure can also be used to distinguish D. australis and D. muelleri. The spherical oogonia of D. australis, which project above the thallus surface, are conspicuously different from the angular embedded oogonia of D. muelleri. Detailed comparative studies on other species of Dictyopteris are now required to ensure that reproductive characters are used not only to define species of Dictyopteris but also to effectively circumscribe the genus.