I spotted this tree while out walking the other evening, and I suspect it's hakuunboku a.k.a Styrax obassia or Fragrant styrax. The silvery gray bark slides smoothly over the musculature of the trunk like a tight fitting sleeve, and tucked under it's veined oval leaves were these lovely white blossoms. If it is indeed hakuunboku, it is a tree native to Japan as well as Korea and China. (It's in the same family as Japanese snowbell (ego-no-ki) or Styrax japonicus.) I'd never noticed it in bloom before although I've always found the bark quite eye-catching. It reminds me of Ironwood, a.k.a. American Hornbeam Carpinus caroliniana, another smooth barked tree that I know from long walks on the family land in Michigan.
The blossoms pictured here should also be quite fragrant, although I confess I did not pause to sniff, only photograph. If they are indeed as delightfully smelly as they are purported to be I would suspect they are a pollinator favorite. I'd also like to think that the ever-increasing number of butterflies I see floating about the city find the tree a good home complete with a pleasant drink bar. Any ideas?