<p><strong>Affinities of four freshwater putative “Chantransia” stages (Rhodophyta) in Southern China from molecular and morphological data</strong></p>

Abstract

Four putative “Chantransia” isolates were collected from four locations in Hubei and Yunnan Provinces, China. Morphological analyses were conducted on all isolates. Two specimens (HB26 and YN2) fit the morphological description of A. pygmaea, while the other two isolates (YN1 and YN3) varied in morphology, but were within the circumscription of Audouinella hermannii. Due to the fact that the morphological characters of the “Chantransia” stages of order Batrachospermales and the species of genus Audouinella are too similar to be distinguished, a molecular analysis was performed to clarify the phylogenetic position of these four isolates based on rbcL and psbA sequences. Two “pygmaea” specimens collected from Jiugong Mountain, Hubei Province (HB26) and Shimen Gorge, Yunnan Province (YN2), such as S. jiugongshanensis and S. shimenxiaensis, are proposed primarily based on the DNA sequence data generated in this study. The description of these two new species provides more molecular data for phylogenetic analysis of the genus Sheathia. In addition to these newly described species, the results strongly support that those “hermannii” isolates (YN1 and YN3) collected from Yunnan Province were the “Chantransia” of S. arcuata. However, their gametophyte stages have not been found, meaning that critical diagnostic morphological features were unavailable and molecular methods were the only means for ascertaining their phylogenetic position. Considering the extensive application of the rbcL and psbA genes in phylogenetic analyses of freshwater red algae, we recommend using these two genes to identify species when no morphological characteristics are available.

Thorea baiyunensis sp. nov. (Thoreales, Rhodophyta) and T. okadae, a new record from China

“…Several studies have confirmed that it is difficult to distinguish “ Chantransia ” stages from true Audouinella based only on morphological characteristics, which often hinders species identification and brings confusion to the classification system of freshwater red algae ( Chiasson et al 2005 ; Necchi and Oliveira 2011 ; Han et al 2020 ). More surprising is that even individuals with completely different gametophyte morphology, belonging to different species, genera or orders, may also produce “ Chantransia ” stages with extremely similar morphology.…”

“…However, molecular analysis confirmed that they were not Audouinella taxa but the “ Chantransia ” stages of two different Thorea species, T. okadae and T. baiyunensis . Based on sequence data and culture studies ( Pueschel et al 2000 ; Zucchi and Necchi 2003 ; Chiasson et al 2005 , 2007 ; Necchi and Oliveira 2011 ; Han et al 2020 ), eleven species of orders Batrachospermales and Thoreales have been confirmed to form “ Chantransia ” stages similar to A. pygmaea in morphology.…”

“…With the widespread application of molecular data in the taxonomy of freshwater red algae, the view that morphologically simple organisms have considerable genetic diversity and species richness has been widely recognized ( Johnston et al 2018 ; Han et al 2020 , 2021 ). In the past few years, several new species of the Batrachospermales and Thoreales were proposed based on the “ Chantransia ” sporophyte generation, such as T. quisqueyana , Sheathia shimenxiaensis J.-F.Han, F.-R.Nan et S.-L.Xie, S. jiugongshanensis J.-F.Han, F.-R.Nan et S.L.Xie, and S. qinyuanensis J.-F.Han, F.-R.Nan et S.L.Xie ( Johnston et al 2018 ; Han et al 2020 , 2021 ). In this article, based on the rbc L and COI-5P sequences, all five samples utilized in this study were unquestionably proved to be the “ Chantransia ” stages of two species of genus Thorea , whose gametophytes have never been reported in China before.…”

“…In terms of morphological characters, the “ Chantransia ” stages of the Thoreales are very similar to those of Audouinella taxa, although some studies have indicated that thallus color can be used as a reliable character ( Zucchi and Necchi 2003 ) to distinguish true Audouinella (reddish) from “ Chantransia ” (bluish). However, “ Chantransia ” stages of the Thoreales can be brownish ( Chiasson et al 2007 ), and some species of Sheathia can be brownish to reddish in addition to bluish ( Han et al 2020 ). Thus, morphological characteristics that can unequivocally distinguish them have not been found ( Pueschel et al 2000 ; Chiasson et al 2005 ).…”

“… heterospora S.L.Xie & Y.J.Ling were “ Chantransia ” of T. hispida rather than belong to Audouinella . Besides, numerous surveys ( Pueschel et al 2000 ; Zucchi and Necchi 2003 ; Chiasson et al 2005 , 2007 ; Necchi and Oliveira 2011 ; Han et al 2020 ) demonstrated that eleven species, including members of the Thoreales ( T. hispida and N. tortuosa Yoneda & Yagi), were associated with “ A. pygmaea ”.…”