There is a concept in all arts called rhythm, and if I've understood
correctly, it amounts to repetition. In a small space, three very
different
but equally prominent trees look like they've just been plonked in. Three
of
the same species give unity to the area. Of course you could use three
citrus
trees -- they're probably similar enough to give rhythm.

I imagine that one could probably get away with three different trees if one
was experienced enough to understand which combinations work together -
since that's not me, I appreciate your advice on how to make a more
successful mix!

I had a look at the Bower of Beauty. It looks like an interesting plant,
very close to what I imagined growing up the pergola - large white flowers
and a tropical feel.

I might take a look at the smaller varieties of Frangipani, for plants which
can take the heat in general. Apparently there are some evergreen varieties
out there.

C.