Prunus cerasifera (naturalized and cultivated) and P. salicina (mostly, if not pretty much entirely cultivated).

Thanks! They look much more like the P. salicina. Pretty things, regardless.

Cherry plum produces mostly solitary flowers, in a more pure white. Purple-leaved forms with pink flowers are prevalent in gardens. These (and various other Prunus) may be grafted onto typical green-leaved, white-flowered cherry plum, show cherry plum rootstock sprouts that have not been removed.

Japanese plum produces mostly clustered flowers, 3 or more per bunch, often of a rather greenish white.

Due at least in part to most of the flowers springing from the stems by themselves, instead of in sets of 3 or more, cherry plum has a more diffuse appearance in flower, without so much of the strands-of-popcorn appearance that Japanese plum often presents when full out.