Museomics in Lamiaceae: Resolving the taxonomic mystery of Pseudomarrubium

The monotypic genus Pseudomarrubium is perhaps the most poorly understood taxon within the subfamily Lamioideae (Lamiaceae). While advances in molecular phylogenetics have clarified the phylogeny and taxonomy of Lamioideae, the systematic placement of Pseudomarrubium remains unclear, as it has never been tested using molecular phylogenetic analyses due to an inaccessibility of plant material. In this study, we used high-throughput next-generation sequencing to infer the systematic placement of Pseudomarrubium based on old herbarium collections as well as silica gel-dried leaves. Phylogenomic analyses demonstrate that Pseudomarrubium is a member of tribe Phlomideae and nested within Phlomoides, and a new combination, Phlomoides eremostachydioides, is proposed. The study highlights that herbarium-preserved samples, even very old ones, are invaluable resources that can be used to generate reliable genome-scale data and be used for molecular phylogenetic inquiries.