Taxonomic reassessment of the Indo-Pacific Scytosiphonaceae (Phaeophyceae):Hydroclathrus rapanuiisp. nov. andChnoospora minimafrom Easter Island, with proposal ofDactylosiphongen. nov. andPseudochnoosporagen. nov.

Abstract

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.

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

“…Moreover, our current study is also the first to document the growth and development of I. stellata sporophytic microthalli in culture. Accordingly, I. stellata produces plurangia on microthalli, which is typical of taxa within the 'Hydroclathrus group' (as compared to taxa within the 'Scytosiphon group') (Santiañez et al 2018b). Finally, similar to recent works on other closely related taxa (e.g.…”

“…We expect that more detailed taxonomic and molecular phylogenetic studies on these genera will result in discoveries and/or further systematic revisions within the Scytosiphonaceae as what has been demonstrated in recent studies (e.g. McDevit & Saunders 2017;Huisman et al 2018;Santiañez et al 2018aSantiañez et al , 2018bSantiañez & Kogame 2019).…”

“…Moreover, based on phylogenetic and morphoanatomical data, we also remove I. quadriseriata from its original genus assignment and transfer and synonymize it under R. intricata (see proposal below). Taking all these taxonomic changes in consideration, we thus consider Iyengaria as a monotypic genus similar to other genera under the 'Hydroclathrus group' (Santiañez et al 2018b). Moreover, our current study is also the first to document the growth and development of I. stellata sporophytic microthalli in culture.…”

“…Cho & Kogame (as Chnoospora implexa J. Agardh; Kogame 2001) and different from the ectocarpoid plurangia on microthalli of Colpomenia peregrina Sauvageau (Kogame & Yamagishi 1997), Hydroclathrus clathratus (C. Agardh) M. Howe (Toste et al 2003), and R. australis (Santiañez & West 2019). Production of plurangia on microthalli has been reported in culture of scytosiphonacean species within the 'Hydroclathrus group' sensu Santiañez et al (2018b): R. australis (Santiañez & West 2019), P. implexa (Kogame 2001), H. clathratus (Toste et al 2003), and C. peregrina (Kogame & Yamagishi 1997), among others. Of these, the last three species were known to also produce unilocular sporangia on microthalli.…”

Species diversity and distribution of the genus <italic>Colpomenia</italic> (Scytosiphonaceae, Phaeophyceae) along the coast of China

“…The present study focuses on Colpomenia specimens collect-rophytes, and (2) species with elongate or tubular thalli producing only unilocular zoidangia on sporophytes (Kogame et al 1999, Boo et al 2011, Lee et al 2012). However, Santiañez et al (2018) The globular Colpomenia species usually contain oxygen generated by photosynthesis, making them buoyant. When oysters are the substrate, they can become buoyant and drift with the current, earning members of the globular species the moniker "oyster thieves" (Blackler 1967, Vandermeulen 1984.…”