I remember the last time we were in the fabulous botanical garden called Lotusland in Santa Barbara our guide pointed to a Dawn Redwood growing there and said the tree was incredibly rare and was one of only a handful in the US. It turns out that the Boston Public Garden has 2 of them and they have been there for years.
I doubt the tree is a rare as the California guide said. Either that or Boston Garden is even more botanically diverse than I had imagined. Well done Boston!