1 large sweet potato, peeled and cut into 2-inch cubes
Mince four garlic cloves; transfer to a small bowl. Juice half of the orange; add to bowl. Stir in the marmalade, lemon juice, honey, parsley, paprika, oregano, salt, thyme and pepper. With fingers, carefully loosen skin from the turkey; rub 1/2 cup marmalade mixture under the skin.
Thinly slice remaining orange half; place under the skin. Brush turkey with remaining marmalade mixture. Place remaining garlic cloves inside the cavity. Tuck wings under turkey; tie drumsticks together.
Combine the celery, carrots, onion and potatoes in a roasting pan. Place turkey, breast side up, over vegetables.
Bake at 325° for 3-1/2 to 4 hours or until a thermometer reads 180°, basting occasionally with pan drippings. Cover loosely with foil if turkey browns too quickly. Cover and let stand for 20 minutes before carving.