Thanks for reading and posting a comment. You are not alone, I'm sure. Most Americans are probably unfamiliar with Umeboshi plums and their products, especially since the plums are not seen in U.S. mainstream markets. They are part of the fruit landscape in Japan though. If we only had more yard, I would try growing the tree here in South Jersey.
Also, just fyi, I just heard from a woman in Tokyo who writes a blog called 'Blue Lotus'. She has a lot of great photos of life in Tokyo and Japanese foods, including the Umeboshi plums, Umeshu liqueur and Ume Jam. I'm going to add her links to the bottom of the article now, if you want to check her site out.