1. Weigh or lightly spoon flour into dry measuring cups; level with a knife. Combine flour, sugar, flaxseed, if desired, baking powder, and salt in a large bowl, stirring with a whisk.
2. Combine buttermilk, lemon rind, and eggs in a medium bowl, stirring with a whisk. Add buttermilk mixture to flour mixture, stirring just until moist. Gently fold in blueberries and peaches.
3. Heat a nonstick griddle or nonstick skillet over medium heat. Pour 1/3 cup batter per pancake onto pan. Cook over medium heat 2 to 3 minutes or until tops are covered with bubbles and edges look cooked. Carefully turn pancakes over; cook 2 to 3 minutes or until bottoms are lightly browned. Serve with butter. Top with blueberries, if desired.