Pharmaceutical potential of willow leaves in terms of salicylic alcohol content

Salicis cortex has analgesic, anti-inflammatory, antipyretic, and anti-rheumatic properties, primarily due to the content of salicylic alcohol derivatives (SAD) and other phenolic compounds . The Pharmacopoeia Europaea monographs willow bark and does not specify a particular species but requires a minimum content of 1.5 % SAD. This study aimed to determine whether the leaves of certain willow species could also be pharmaceutically relevant due to their SAD concentration, to identify species with high SAD levels, to figure out ideal harvest times, to investigate intraspecific variability, and to determine differences between the sexes in terms of SAD content, including less-studied species . Using a UPLC®-RP18-PDA method, 12 willow species with 42 individuals were analyzed. Concerning the average content of the entire observation period, the following species were identified as particularly SAD-rich (mean ± standard deviation): S. purpurea (6 ± 4 %), S. aurita (3 ± 4 %), S. fragilis (3.2 ± 2.3 %), S. cinerea (2.5 ± 3.0 %), and S. lapponum (1.7 ± 1.4 %). S. daphnoides (0.11 ± 0.20 %) and S. caprea (0.08 ± 0.21 %) are displayed as SAD-poor species. Statistical analysis revealed a slight intraspecific variation, but the interspecific variability of the SAD content was higher. The SAD values were significantly higher in mid- and late summer, except for S. purpurea (May) and S. caesia (June), as well as in 2019 compared to 2018. Moreover, no significant effect of sex could be detected. Considering the high costs of producing willow bark extracts, supplementing with willow leaves, particularly from SAD-rich species and genotypes, could be beneficial. • Analysis of 12 willow species with 42 individuals for their salicylic alcohol content. • Willow leaves are pharmaceutical interesting and could be used in addition to the bark and shoots. • S. purpurea leaves contain the most salicylic alcohol derivatives, even more than in the bark. • Leaves of S. daphnoides and S. caprea contain the least salicylic alcohol derivatives. • High interspecific and slight intraspecific variability in salicylic alcohol content.