So I settled on a wood which grows locally and which was cut to order with a chain saw and then planed - edges and one side only: it's called aceituno. It's not as nearly-white as holly which doesn't grow in Nicaragua anyway; and it has a more interesting grain than poplar which also doesn't grow in Nicaragua anyway. But it's a nice addition.
The botanical name of aceituno is Simarouba glauca and it has lots of common names in addition to aceituno. The wood's used for things like furniture components and musical instruments.
It's lovely and cool looking. Here's a close up of a piece before the first coat of marine varnish.
And here are the floor boards themselves shown leaning upstairs in our first house after their first coat of varnish. The varnish darkens it a bit...but not too much.
