Untargeted metabolomics as a new perspective for assessing taxonomic boundaries in alpine Rubus genus

The development of a robust taxonomy for the genus Rubus remains a real challenge, due to apomictic reproduction and hybridization that led to a very large number of "taxa" with undefined frontiers. Using an untargeted metabolomic approach and a two-year leaf sampling along an elevational gradient in the French Alps we provide new tools to assess boundaries between nine Rubus taxa. Multivariate analyses on ionic intensity matrices (of 566 and 668 features for 2023 and 2024 sampling respectively) have shown that R. idaeus species, the two sections Corylifolii and Rubus, and Caesii section related taxa, formed three distinct super groups. Thirty-eight compounds have been annotated, including 8 detected in genus Rubus for the first time. Discriminant compounds have been annotated, allowing to propose ursane triterpenoids, flavonoids glycosides, lignans and gallotannins as taxonomic classifiers of the genus Rubus. Among those, quercetin - and kaempferol - 3-O-methylglutaryl hexoside were detected at higher levels in R. idaeus, whereas neolignans glycosides have been mostly detected in sections Corylifolii and Rubus. The intermediate position of Caesii between the two others did not allow to propose specific biomarkers of the section. The need for a precise and detailed description of the phytochemical profiles of the various Rubus subgroups is reinforced by the growing use of some of these compounds in pharmacology and cosmetics.