They appear too large, too round and the wrong colour for Damsons, which are similar in shade to Blueberries with a bloom to the skin. But you already know they aren't. I'm not sure what you mean by 'they were grafted' when you bought them. If they were advertised as seedlings they wouldn't be grafted. And if they were grafted onto seedlings the grafted variety should have been named by the seller. Can you clarify?

There are many purple plums. If you included a picture of leaves and of full fruits not cut up it would make it possible to guess some possibilities. It looks like an asian plum, and that can be confirmed by the leaf shape.

Scott

flora uk: I know next to nothing about fruit trees, but they were grafted at the base. There was nothing I remember about the sellers ad saying they were.

scottfsmith: I'll get a pic of the leaves posted as soon as I can. Working out of town for the next few days. I may have a pic of the fruits on my phone.

Thanks for the replies.

Looks like a satsuma from the color of the meat

It looks like a japanese plum, prunus salcifolia. The fruits are deep red, small and juicy, sometimes called a beach plum, I think. The only other possibility I can come up with is the cherry plum, prunus cerasifera - a great hedging plum which makes really good jam.