Why is your dog eating the leaves of black eyed susan?

No one really knows, although it is common for dogs to eat various plants when they can. It appears that certain dogs like to eat certain plants, and the type of plant will vary from dog to dog. There are hypotheses that link this to an instinctive drive to balance their diet, the presumption being that their food is lacking in a trace mineral. Others feel that this is because the dog simply likes the taste of that plant.

So long as your dog doesn't develop diarrhea or other health problems and the plant isn't toxic (black-eyed susans are not toxic to dogs, as far as I know), then feel free to accept it as a special quirk of your dog.