Pyrrolizidine alkaloids (PAs) represent a class of typical SMs, which are constitutively formed in plants containing them and mediating plant-herbivore interactions. More than 400 PAs have been identified from approximately 6000 angiosperm species. Great diversity of PAs was found in many plants, especially in Jacobaea and Senecio plants. Leaf-tissue PA variation was found between plant species, individual plants of the same species, and even among different organs within one plant. This variation was determined by genetics, but also influenced by environmental factors. A few studies have been conducted to investigate the leaf-surface PA variations. According to the previous work on J. vulgaris plants and the Jacobaea hybrid plants, leaf-surface and leaf-tissue PA profiles of a particular genotype were different from one another: a number of PAs that were present in the leaf tissue at relatively high concentrations were absent from the leaf surface. Nevertheless, positive correlations were found for the concentration of all PAs, that of the free bases, as well as that of a number of individual PAs between the leaf surface and leaf tissue. Moreover, the total amount of PAs present on the surface of the leaves was less than 0.01% of the total amount present in the leaf tissue. This makes it clear that the relationship between the leaf-surface and leaf-tissue SMs can offer an important new angle to study the insect-plant interaction mediated by plant SMs. © 2020, Springer Nature Switzerland AG.