Resolving the taxonomy of the Polysiphonia scopulorum complex and the Bryocladia lineage (Rhodomelaceae, Rhodophyta)

Abstract

Cryptic diversity is common among marine macroalgae, with molecular tools leading to the discovery of many new species. To assign names to these morphologically similar species, the type and synonyms have to be examined, and if appropriate, new species must be described. The turf‐forming red alga Polysiphonia scopulorum was originally described from Rottnest Island, Australia, and subsequently widely reported in tropical and temperate coasts based on morphological identifications. A recent study of molecular species delineation revealed a complex of 12 species in Australia, South Africa, and Europe. These species are placed in a taxonomically unresolved lineage of the tribe Polysiphonieae. The aim of this study was to resolve the genus‐ and species‐level taxonomy of this complex and related species using molecular and morphological information. Three morphologically indistinguishable species of the complex were found at the type locality of P. scopulorum, preventing a straightforward assignment of the name to any of the molecular lineages. Therefore, we propose a molecularly characterized epitype. Polysiphonia caespitosa is reinstated for the only species found in its type locality in South Africa. We describe seven new species. Only one species of the complex can be morphologically recognized, with the other eight species indistinguishable based on morphometric analysis. The studied complex, together with another seven species currently placed in Polysiphonia and two Bryocladia species, formed a clade distinct from Polysiphonia sensu stricto. Based on observations of Bryocladia cervicornis (the generitype), we describe our seven new species in the genus Bryocladia and transfer another nine species from Polysiphonia to Bryocladia.

On the track of unknown algae

“…As reported in this issue of the Journal of Phycology , Díaz‐Tapia and Verbruggen (2024) have carried out an extensive study of the biodiversity of turf‐forming red algae. Turfs are of particular interest in the context of global change, as they are globally seen to replace stands of larger canopy‐forming algae (Filbee‐Dexter & Wernberg, 2018).…”

“…Now, in this issue of the Journal of Phycology , Díaz‐Tapia and Verbruggen (2024) have provided the taxonomic and nomenclatural conclusions of their analyses. Struck et al.…”

“…'s (2020) study of six tiny cryptic Gayliella species from Brazil resulted in the proposal of four new species and a new combination that required epitypification. Determining correct names for all 12 cryptic species previously attributed to Polysiphonia scopulorum worldwide (Díaz‐Tapia & Verbruggen, 2024) is therefore a major achievement given the complexity of the phylogenetic and taxonomic information. It required seeking out all valid names and determining their types, over a large geographical area.…”

“…Díaz‐Tapia and Verbruggen (2024) contribute to a better knowledge of cryptic species, helping to track these unknown algae and to bring them into a formal taxonomic framework. This is important for understanding global and regional biodiversity, for determining the origins and spread of invasive species (e.g., van der Loos et al., 2023), for biodiscovery (Payo et al., 2011), and for marine conservation more broadly (Payo et al., 2013).…”