Diversity of the genus <italic>Sheathia</italic> (Batrachospermales, Rhodophyta) in northeast India and east Nepal

Abstract

Freshwater red algae of the order Batrachospermales are poorly studied in India and Nepal, especially on a molecular basis. During a survey in northeast India and east Nepal, six populations of the genus Sheathia were found and analyzed using molecular and morphological evidence. Phylogenetic analyses based on the rbcL gene sequences grouped all populations in a large clade including our S. arcuata specimens and others from several regions. Sheathia arcuata represents a species complex with a high sequence divergence and several smaller clades. Samples from India and Nepal were grouped in three distinct clades with high support and representing new cryptic species: a clade formed by two samples from India, which was named Sheathia assamica sp. nov.; one sample from India and one from Nepal formed another clade, named Sheathia indonepalensis sp. nov.; two samples from Nepal grouped with sequences from Hawaii and Indonesia (only 'Chantransia' stages) and gametophytes from Taiwan, named Sheathia dispersa sp. nov. Morphological characters of the specimens from these three species overlap one another and with the general circumscription of S. arcuata, which lacks the heterocortication (presence of bulbous cells in the cortical filaments) present in other species of the genus Sheathia. Although the region sampled is relatively restricted, the genetic diversity among specimens of these three groups was high and not closely related in the phylogenetic relationship with the other clades of S. arcuata. These data corroborate information from other groups of organisms (e.g., land and aquatic plants) that indicates this region (Eastern Himalaya) as a hotspot of biodiversity.

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

“…Sheathia is the only genus in the Batrachospermales in which heterocortication has been identified and used as a taxonomic character (Salomaki et al 2014). All species with heterocortication form a well-supported subclade with the exception of S. exigua which is sister to a large clade of homocorticate species (Salomaki et al 2014, Necchi et al 2019c. Salomaki et al (2014) hypothesized that heterocortication was subsequently lost in the homocorticate species and our study supports this view.…”

“…and Washington were gametophytes such that morphological characters typically used to distinguish species in Sheathia were assessed including measurements of gametophyte whorls and fascicle cell number, carpogonia, carpogonial branch, carposporophytes, and carposporangia (Salomaki et al 2014, Necchi et al 2019c). The specimens from Finland, Ireland, and Poland were of the chantransia stage.…”

“…Plants monecious or dioecious; purple to reddish with yellow-brownish hue, sometimes dark bluish; branching irregular; whorls well-developed, confluent, barrel-shaped or spherical, 320-890 µm diameter; main axis covered in regular, cylindrical cortication (homocortication); primary fascicles with cells ranging from cylindrical to ellipsoidal and obovoidal, (9-) 12-18 (-20) cells; secondary fascicles few and sparse; spermatangia spherical or subspherical, terminal on primary fascicles, 4.8-5.3 µm in diameter; carpogonial branch composed of cells similar to the fascicles, straight, developing from the periaxial, proximal cells of primary fascicles and occasionally from distal cells of primary fascicles, 2-13 cells; involucral filaments, short or long, composed of cylindrical or ellipsoidal cells; carpogonia with clavate to ellipsoidal trichogynes, 21-42 µm in length, 5.6-10.3 µm diameter; carposporophytes 1-4 per whorl, 68-142 µm in diameter; gonimoblast filaments densely arranged, composed of 2-4 barrel-shaped to cylindrical cells; carpospo-majority of specimens used for sequence analyses are chantransia stage sporophytes. S. dispersa has been reported as gametophytes from Nepal and Taiwan, but as sporophytes (chantransia) from Indonesia and numerous collections from the Hawaiian Islands (Chou and Wang 2006, Chiasson et al 2007, Carlile and Sherwood 2013, Johnston et al 2014, Necchi et al 2019c. At least in the Hawaiian Islands, there have been many collections and a large-scale survey which did not yield gametophytes (Carlile and Sherwood 2013).…”

“…Among the homocorticate species, identification of species based on morphological characters would be difficult given the overlap in characters typically used to distinguish species. Even the most recent reports on the genus have noted the lack of defining morphological characters when describing new species (Necchi et al 2019c, Szinte et al 2020. Although DNA sequence data are needed to make a positive species identification, geographic pattern of distribution could be employed to narrow the identification to one or two species.…”

Substratum‐associated microbiota

“…Similarly, molecular analysis of a distinct clade of Batrachospermum by Necchi, Garcia Fo, Paiano, and Vis 2019 A new species of Batrachospermales, Sheathia matouensis sp. nov., described from fresh spring water in Shanxi province, China, can be distinguished from similar taxa based on rbcL and psbA molecular data and morphological differences in the carpogonium and smaller whorls (Han et al, 2019) (Necchi, West, et al, 2019).…”