Integrative taxonomy reveals an ancient species of the genus <i>Trollius</i> (Ranunculaceae), long hidden under a hybrid name

Abstract In the course of the ongoing taxonomic revision of the genus Trollius L. in Asia, conducted by the first author since 2017, the inventory and in-depth study of interspecific hybrids were high priority tasks. Several interspecific hybrids of Trollius have extensive distribution ranges, and their presence in regional floras is extremely noticeable and should be adequately reflected in any regional flora/synopsis/checklist. We performed a study of long known taxon considered to be an interspecific hybrid, T. asiaticus × T. altaicus, which has a vast distribution range in the Asian part of Russia, implementing morphological and biogeographic methods together with molecular genetic techniques: chloroplast DNA sequencing, fragment analysis, and a haplotype network approach. The taxon turned out to be not the interspecific hybrid T. asiaticus × T. altaicus but a species of ancient origin with an island relict distribution range, participating in modern/current hybridization throughout the range. In the light of the results obtained a species new to science—Trollius elpasianus Serebryanyi sp. nov.—is herein described; an updated map of its distribution range is provided.