Status, morphology, and phylogenetic relationships of Iyengaria (Scytosiphonaceae, Phaeophyceae), a brown algal genus with a disjunct distribution in the Indian Ocean

SUMMARY The taxonomy, classification, and phylogenetic relationships of the brown seaweed genus Iyengaria with other members of the family Scytosiphonaceae remain poorly understood. In this study, we addressed some problems in the systematics (taxonomic and classification status) and phylogenetic position of Iyengaria based on our studies on the generitype Iyengaria stellata from Kuwait and South Africa. We confirm that I. stellata is conspecific with Colpomenia capensis based on molecular and morpho‐anatomical data and that the species has a disjunct distribution within the Indian Ocean. Also, the distinguishing features of two Iyengaria species (I. nizamuddinii and ‘I. lobocylindrica’) described from Karachi, Pakistan, are within the morphological range of I. stellata. Hence, these two taxa are considered here as junior heterotypic synonyms of I. stellata. Our molecular phylogenetic analyses suggested the polyphyly of the genus Iyengaria, with the recently described Iyengaria quadriseriata from India forming close associations with Rosenvingea intricata. As such, we remove I. quadriseriata from the genus Iyengaria and relegate it as a synonym of R. intricata. Consequently, by recognizing only one species, our proposals considerably reduce the species diversity in the genus. Moreover, our culture studies suggested that I. stellata exhibits an alternation of heteromorphic generations, similar to other species in the Scytosiphonaceae. Under culture conditions, I. stellata also produced plurangia on microthalli, confirming its affinity with other phylogenetically close relatives in the ‘Hydroclathrus group’ of the family Scytosiphonaceae such as Colpomenia, Rosenvingea, and Chnoospora.