Hide and seek on the central Kuril Island Simushir: Firstly recorded vascular plant species are confined to specific scattered habitats

The central part of the Kuril Archipelago (the Russian Far East) remains the least studied due to its poor accessibility. Such insufficient floristic data lead to uncertainties in the floristic subdivision of the Kuril Islands. We aimed to explore the vascular flora of the Simushir island, the largest one among the Middle Kurils. We revealed 24 new species for the flora of Simushir or Middle Kurils in general, including three species (Callitriche anceps, Carex meyeriana, and Ribes nigrum) that are new for the whole Kuril Archipelago. One-third of species new for Simushir are alien. Almost all the rest of the new species are associated with special types of habitats and can be found only after a detailed study of the island. We reported six new aquatic species for the Middle Kurils, refuting the earlier idea of extreme poverty of the Middle Kurils’ aquatic flora. We found no grounds for drawing a floristic border within the Northern and Middle Kurils, as the floristic similarity between Onekotan (oceanic Northern Kurils), continental Northern Kurils, and Simushir has the same magnitude.