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A new and putatively endemic species ofHydroclathrus,Hydroclathrus rapanuii, is described from the geographically isolated Easter Island in the southeastern Pacific based on morphological and molecular phylogenetic data. It is distinguished from otherHydroclathrusby thalli of unevenly furrowed thin membranes, and angular, block-like plurangial sori. Our phylogenetic analyses indicated thatH. rapanuiiis closely related to the generitypeHydroclathrus clathratus. We also report on the morphology and phylogeny ofChnoospora minimafrom Easter I. and elsewhere in the Indo-Pacific Ocean, noting the previously unreported presence of hollow portions in its medulla. Although not collected from Easter I., we herein propose the recognition of two new genera,Dactylosiphongen. nov. andPseudochnoosporagen. nov., based on our three-gene phylogeny and their known morphologies and anatomies.Dactylosiphonis based on the three species currently assigned toColpomenia(C. bullosa,C. durvillei, andC. wynnei) that are genetically and morphologically (i.e. thalli with erect and finger-like tubes arising from a common saccate base) distinct from other members ofColpomenia. The monotypic genusPseudochnoosporais represented by the decumbent, branching, and inter-adhesive species currently known asChnoospora implexa. With the above proposals, we further increase the genus-level diversity of Scytosiphonaceae in the Indo-Pacific Ocean.

The brown algal genus

The brown algal family Scytosiphonaceae has recently received considerable attention resulting in the description of several new genera and species. However, members of the genus Scytosiphon and Petalonia remain polyphyletic. By integrating multi-gene phylogenetic data (mitochondrial cox3 and plastid psaA and rbcL genes) with their known morpho-anatomies and life histories, we herein resurrect Hapterophycus canaliculatus, currently considered a member of genus Scytosiphon, and transfer Scytosiphon tenellus to the genus Petalonia.

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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.

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