Authorized Vendor for Hawthorn. The leaves, flowers, and berries of Hawthorn contain a variety of bioflavonoids; potent antioxidants that appear to be primarily responsible for the cardiac actions of the plant. Despite the emerging studies, researchers have not been able to attribute its use to one specific constituent marker. In fact there are a couple of different markers available in standardized extracts commercially. We believe that the whole herb contains many constituents that work together - as nature intended.