a project of mine is the growing of Canada plum . Prunus Nigra . Pics are to show the distinction in the flowers . First pic with more yellow is American plum. ( actually a hybrid natural cross from a fruit orchard nursery expected cross with European fruit tree May be unique cultivar ) but for this purpose the flowers are correct . The second pic is Canada . Note the red . These are also smaller and less of them . On some the flower pistols are also red but not mine so far , the hint of red/ pink in the petals is also supposed to increase as they fade. This is the first time they are flowering so we will see