Is the exploration of the Socotran flora complete? A new species and the return of a lost Psiadia (Asteraceae)

The island of Socotra is globally renowned for its exceptional biogeographical significance, yet its flora remains incompletely documented. During recent botanical exploration of the island’s northern coastal sector, we discovered a previously unrecognized composite species. Morphological examination and consultation of identification keys demonstrated that the plant belongs to the genus Psiadia (Asteraceae), a lineage centred in Madagascar but extending into eastern Africa and the Arabian Peninsula. Only one species of the genus, P. schweinfurthii, has previously been recorded from Socotra, although it was considered extinct until a recent rediscovery near its type locality. We combined morphological data with two molecular markers (nrITS and psbA-trnH) to assess the taxonomic status of the newly collected lineage and to perform the first molecular study of P. schweinfurthii. Phylogenetic analyses using Maximum Parsimony and Bayesian Inference consistently recover the new species and P. schweinfurthii as a strongly supported sister pair. Genome size estimates further indicate that both Socotran species share similar ploidy levels, with values approximately twice those reported for P. retusa from Réunion. Morphological traits of the new species, including fleshy papillate leaves and reduced achene papillosity, indicate adaptation to xerohaline coastal habitats overlying Jurassic sandstones and siltstones. We describe this taxon as Psiadia yelsok La Montagna & Maděra, sp. nov., and provide its diagnosis, description, and ecological characterization. Both P. yelsok and P. schweinfurthii are extremely range-restricted, each known from a single population with an area of occupancy <10 km2 and exposed to ongoing habitat degradation. We therefore propose a preliminary IUCN assessment of Critically Endangered (CR B2ab(iii)) for both species. The discovery of P. yelsok underscores the incomplete state of botanical exploration on Socotra and highlights the continued importance of integrative taxonomy for documenting and conserving island biodiversity.