We picked these up at Amish while we were in Manhattan this weekend and seriously have no idea what they are. Well, they are tiny green plums, but beyond that, I am stumped. I thought maybe they were greengage plums, but they are smaller than that, I think. Matt thought they were Japanese plums (ume?) at first but now we are not sure. They have a very clear (not smudgy like some plums) bright green skin and matching green flesh. The guy at the store said they were grown in South America, but I don't think that makes much difference. Here's another picture with my very normal sized thumb in it for perspective. Tiny, tiny plums.