Revealing hidden diversity in the Sheathia arcuata morphospecies (Batrachospermales, Rhodophyta) including four new species

Abstract

The freshwater red algal genus Sheathia contains species with heterocortication (both bulbous and cylindrical cells covering the main axis) and homocortication (only cylindrical cells). When the genus was proposed, the species with heterocortication were revised, but all specimens with homocortication were assigned to Sheathia arcuata with the caveat that it may represent a species complex. Recent studies have described new species with homocortication and S. arcuata has been rendered paraphyletic. In the current study, new sequences of the rbcL and 5′ region of the cytochrome c oxidase subunit I markers were combined with previously published data to construct a robust phylogeny and circumscribe new species. Four new species, S. abscondita, S. californica, S. plantuloides, and S. transpacifica are proposed. Examination of morphological characters among homocorticate species show no diagnostic characters to distinguish among species, whereas S. plantuloides is only known from sporophytes (chantransia) so it lacks the typical morphological characters derived from the gametophytes for comparison. Although DNA sequence data would be needed to make a positive species identification, geography could be employed to narrow the identification to one or two species. The genus is geographically widespread having been recorded from oceanic islands and five continents, whereas the individual species typically occur on a single continent. With this study, the number of species recognized in Sheathia is raised to 17; seven heterocorticate and 10 homocorticate, making this genus one of the most species rich in the Batrachospermales. As well, the resulting phylogeny provides insights into the evolution of heterocortication in Sheathia.

Sheathia yunnanensis, a new species of freshwater red alga (Rhodophyta: Batrachospermales) from Yunnan, China

“…All species within the complex were homocorticated (Necchi et al 2019). Vis et al (2020) made a detailed research on the hidden diversity of this Sheathia arcuata morphospecies and constructed a robust phylogeny based on morphological characteristics, DNA sequence data and geographic distribution. Sheathia species from China, namely, S. hongdongensis , S. jinchengensis and S. matouensis have been revised as synonymies of S. longipedicellata (Vis et al 2020).…”

“…Vis et al (2020) made a detailed research on the hidden diversity of this Sheathia arcuata morphospecies and constructed a robust phylogeny based on morphological characteristics, DNA sequence data and geographic distribution. Sheathia species from China, namely, S. hongdongensis , S. jinchengensis and S. matouensis have been revised as synonymies of S. longipedicellata (Vis et al 2020). In this study, we reached a similar conclusion, the samples from China ( S. jinchengensis , S. hondongensis and S. matouensis ) were all grouped within a high supported clade based on rbc L, COI‐5P, psb A and concatenated rbc L + COI‐5P.…”

“…According to the morphoanatomical characteristics used for the Sheathia species in relevant taxonomic papers (Kumano 2002, Salomaki et al 2014, Necchi et al 2019, Vis et al 2020), the vegetative structures were examined and measured using a microscope equipped with a charge‐coupled device (DP72; Olympus, Tokyo, Japan) for photographing.…”

“…The genus Sheathia Salomaki & M.L.Vis, belonging to the order Batrachospermales (Florideophyceae, Rhodophyta), is a recently proposed genus to accommodate species of the Batrachospermum section Helminthoidea based on both morphological and molecular methods (Salomaki et al 2014). Sheathia is widespread geographically with species recorded from oceanic islands and five continents except South America, and it inhabits freshwater habitats such as unpolluted clean streams, rivers or springs (Kumano 2002, Salomaki et al 2014, Vis et al 2020). This genus contains two morphological groups, namely, species characterized by heterocortication (both bulbous and cylindrical cells covering the main axis) and species characterized by homocortication (only cylindrical cells).…”

“…The genus Sheathia Salomaki & M.L.Vis, belonging to the order Batrachospermales (Florideophyceae, Rhodophyta), is a recently proposed genus to accommodate species of the Batrachospermum section Helminthoidea based on both morphological and molecular methods (Salomaki et al 2014). Sheathia is widespread geographically with species recorded from oceanic islands and five continents except South America, and it inhabits freshwater habitats such as unpolluted clean streams, rivers or springs (Kumano 2002, Salomaki et al 2014, Vis et al 2020. This genus contains two morphological groups, Sheathia yunnanensis, a new species of freshwater red alga (Rhodophyta: Batrachospermales) from Yunnan, China Kun-Peng Fang, Fang-Ru Nan, Jia Feng, Jun-Ping Lv, Qi Liu, Xu-Dong Liu and Shu-Lian Xie K.-P. Fang, F.-R. Nan, J. Feng, J.-P. Lv, Q. Liu, X.-D. Liu andS.-L. Xie (https://orcid.org/0000-0003-2349-2071) ✉ (xiesl@sxu.edu.cn), School of Life Science, Shanxi Key Laboratory for Research and Development of Regional Plants, Shanxi Univ., Taiyuan, China. namely, species characterized by heterocortication (both bulbous and cylindrical cells covering the main axis) and species characterized by homocortication (only cylindrical cells).…”