1. Preheat oven to 375°.
2. Weigh or lightly spoon potato starch and flours into dry measuring cups; level with a knife. Combine potato starch, flours, baking soda, and next 6 ingredients (through nutmeg) in a medium bowl; stir with a whisk. Make a well in the center of mixture. Combine pumpkin and next 6 ingredients (through eggs); stir with a whisk. Add to flour mixture, stirring just until moist.
3. Place 16 paper muffin cup liners in muffin cups; coat liners with cooking spray. Spoon batter into prepared cups, and sprinkle with pumpkinseed kernels and turbinado sugar. Bake at 375° for 21 to 23 minutes or until muffins spring back when lightly touched. Cool 10 minutes in pan on a wire rack; remove from pan. Cool completely on wire rack.