Are integrative systematic tools efficient toward unraveling species diversity with the genus Jania (Corallinaceae,...

The articulated genus Jania currently comprises 54 accepted species, making it the fourth most speciose genus among corallines, following Lithophyllum, Amphiroa, and Lithothamnion. Unlike these other genera, Jania is relatively easy to identify at a generic rank. However, morpho-anatomical characters are insufficiently discriminant for species identification, making DNA sequences essential for reliable species delimitation. We evaluated species diversity within Jania using the most comprehensive sampling to date, spanning a broad geographic range with a focus on the Mediterranean and Caribbean regions. Our data set comprised 186 specimens from the National Herbarium of the Muséum national d'Histoire naturelle (PC), including four type specimens with the basionyms Jania micrarthrodia, Corallina polydactyla, Corallina mauritiana, and Jania digitata. We also incorporated publicly available sequences from GenBank and Barcode of Life Data System (BOLD) to delimit species and infer their phylogenetic relationships using the psbA and COI genes. Through an integrative taxonomic approach, combining morpho-anatomical traits, molecular systematics, and biogeography, we delineated 39 putative species-28% fewer than the currently accepted number. Most of the putative species had a restricted distribution, whereas five were widely distributed. We determined seven species from the European Atlantic and Mediterranean seas and six from the Caribbean. Furthermore, we demonstrated that intergenicular morphometry is an unreliable trait for species identification, highlighting the morphological plasticity of Jania. Many putative species remained unidentified (67%), while some of those putative species included specimens with different identifications. Additional sequences of type specimens would be crucial for further resolving taxonomy and bridging the gap between type-bearing name and putative species delineated based on molecular data.