Sweet Woodruff (Galium odoratum L.)—More than Just Coumarin: From Fundamental to Biomass Valorization

Galium odoratum (L.) Scop., commonly known as sweet woodruff, is a perennial European woodland herb traditionally used as a medicinal and aromatic plant. Its characteristic sweet, hay-like scent is mainly linked to coumarin, which is formed from glycosidically bound melilotoside precursors during wilting and drying. However, the phytochemistry of G. odoratum extends beyond coumarin. The species also contains iridoid glycosides, coumarin-related melilotosides, caffeoylquinic acids, flavonoids, and volatile constituents. This review summarizes current knowledge on traditional use, phytochemical constituents, metabolite dynamics, biological and ecological relevance, toxicology, and potential applications. Seasonal variation, organ-specific differences, post-harvest metabolism, and differences in analytical methodology affect analytical interpretation of the available data. Reported biological activities are mainly based on isolated constituents, in vitro studies, animal models, or non-standardized extracts, and no convincing clinical evidence is available for defined G. odoratum preparations. Potential applications require standardized plant material, controlled processing, sustainable sourcing, and safety assessment, while the valorization of processing residues may provide an additional route toward more resource-efficient utilization of the species. Overall, G. odoratum should be regarded as a chemically diverse species rather than merely as a source of coumarin aroma.