If I were to be "lost" on a desert island without a serious stash of warfarin, I'd be looking for plants that might contain coumarin derivatives. Note that warfarin is a synthetic coumarin derivative and was found due to uncontrolled bleeding of cattle ingesting silage made from sweet clover. There are various plants such as woodruff, licorice, lavender, and others that contain coumarin derivatives in various concentrations. Hence anti-coagulants can be abundantly found in nature. So not all is lost when mechanical valve patients end up in paradise without a local chemist and coumadin clinic...