Prunus x yedoensis (Yoshino Cherry)
Japan's favourite cherry tree (as it's now become, though this seems to be a relatively recent phenomenon, mostly post-WWII) has a complex origin that is still being studied, but everyone agrees that it's a hybrid that arose in the 18th century. In many ways it behaves like a species cherry. It's easily grown from cuttings and it produces plenty of small, sour fruit.
Here's the most informative article I've found:
Botany Boy gives the parentage as a cross between P. speciosa (syn. P. lannesiana) and P. spachiana f. ascendens (syn. P. pendula f. ascendens) (Innan et al, 1995). But it's possible things have moved on since then.
Yoshino Cherry trees are propagated vegetatively and so are believed to be clonally identical to the original 18th-century cross.
But how then to account for the cultivars, of which there are several? The supposition is that these must be crosses with other taxa. Which means, I suppose, that the fruit sometimes produces seedlings.
I usually think of Yoshino Cherry as being absolutely smothered in blossom, but this is mainly when the tree is young and compact. As you can see from the photos here (an older tree in Swindon's now-moribund Moredon Tree Collection), it eventually develops quite an open canopy. It's still loud with bees and still extremely attractive; anyhow for a couple of weeks in April.
The bark on mature trees has distinctively thick corky lenticels. This tree doesn't look as if it's been grafted. (Most internet sources say that Yoshino cherries are grafted, but some say the opposite.)