This tree planted in Ala Moana Park in Honolulu has simple leaves around 20cm long, panicles of tiny white tulip-shaped flowers, and nuts (dry drupes?) that have a seam around the two halves. The seed is loose inside the shell, and it sounds like just one seed. There was no way I was able to get the shell open or even tear into the thin edge, and I found no open shells.
Great, Tyrlych, thanks. I'm always so relieved to find that it wasn't something I knew the name of last year - I've never heard of Heritiera, but I did wonder if it was Malvaceae (it is) because it reminded me of the labelled Sterculia that was nearby. I see for Heritiera littoralis, Wikipedia says "the looking-glass mangrove is a large tree with wing shaped nuts, which is most easily recognised by the silvery scales on the underside of its leaves, which therefore appear green from top and white from below". That description fits, but the other species have no descriptions, so I have no idea if they have that appearance as well. [Edited]Common name: looking glass mangrove. On the other hand, the Japanese Wikipedia page says this species is known for its buttress roots, so maybe it's not this one. (My browser gives a Translate option at the top).
