Puzzles do not normally grow on trees - but this one is the exception! The proper name for the tree that the nut comes from is Xylocarpus granatum, but it is also known as the Patience Tree or the Cannonball Mangrove. It is found in East Africa and Southeast Asia, and the wood is used locally for making canoes and also for the production of charcoal. The fruit can be the size of a large orange, or even bigger, and in the middle is a woody capsule containing a number of seeds.
The number of seeds can vary apparently, with anything up to 16. However the particular interest for us is the fact that they interlock so beautifully. However putting the pieces back together is not so easy! Another name for this is the Monkey Puzzle Nut, or I suppose you could think of it as nature's own Rubik Cube!