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

The taxonomy, classification, and phylogenetic relationships of the brown seaweed genusIyengariawith 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 ofIyengariabased on our studies on the generitypeIyengaria stellatafrom Kuwait and South Africa. We confirm thatI. stellatais conspecific withColpomenia capensisbased on molecular and morpho-anatomical data and that the species has a disjunct distribution within the Indian Ocean. Also, the distinguishing features of twoIyengariaspecies (I. nizamuddiniiand 'I. lobocylindrica') described from Karachi, Pakistan, are within the morphological range ofI. stellata. Hence, these two taxa are considered here as junior heterotypic synonyms ofI. stellata. Our molecular phylogenetic analyses suggested the paraphyly of the genusIyengaria, with the recently describedIyengaria quadriseriatafrom India forming close associations withRosenvingea intricata. As such, we removeI. quadriseriatafrom the genusIyengariaand relegate it as a synonym ofR. intricata. Consequently, by recognizing only one species, our proposals considerably reduce the species diversity in the genus. Moreover, our culture studies suggested thatI. stellataexhibits an alternation of heteromorphic generations, similar to other species in the Scytosiphonaceae. Under culture conditions,I. stellataalso produced plurangia on microthalli, confirming its affinity with other phylogenetically close relatives in the 'Hydroclathrusgroup' of the family Scytosiphonaceae such asColpomenia,Rosenvingea, andChnoospora.