This is a nice piece of wood from an old fence post. I don't know for sure what the timber is, but considering its age, I'd suspect it's black maire, since that was extensively used for such purposes, as well as for flooring. Back then, a hundred-odd years ago, when our house was built, New Zealand native timbers were not valued as they are today. Nowadays it's far too expensive to waste on a fence post.
It's 110mm tall.
Alas, it's not much use as a vase, not only because there are various holes and cracks present, but also...
...because I delved too greedily and too deep, and burst through its bottom into the tenon.
When I sawed the tenon off, it left this gaping void in its bottom.
It could be fixed, but I'm probably not going to.
Postscript
I've found that one of these disposable plastic tumblers is almost exactly the right size to fit inside the wooden shell.
I'll add some open-cell self-adhesive foam tape (the sort of stuff you use for sealing windows and the like) around under the rim of the tumbler. That will keep it centred within the vase, stop it from rattling around, and give it a bit of grip so that it won't just fall out while still being easily removable.
It's not 100% perfect as far as shape goes, but it will make the vase somewhat usable as a vase.