Coat geranium leaves with cooking spray; arrange leaves, dull side up, in bottom of a 10-inch tube pan lined with wax paper and coated with cooking spray and flour. Set aside.
Beat margarine at medium speed of an electric mixer until creamy; gradually add sugar, beating well. Add egg whites; beat well.
Combine buttermilk and vanilla, stirring well. Combine cake flour and remaining ingredients; add to margarine mixture alternately with buttermilk mixture, beginning and ending with flour mixture. Mix after each addition. Spoon batter into tube pan. Bake at 325° for 1 hour and 35 minutes or until a wooden pick inserted in center comes out clean. Cool in pan 10 minutes. Remove cake from pan, and let cool completely on a wire rack.