Plants in the wild don't seem to grow over the whole range in which they
might have seemed able to. Maybe its just that some other plant is
better equipped to deal with the other areas, whereas in our collections
there is no competition.
I'm thinking of a native British plant, the Oxlip, or Primula elatior.
It is mostly found in deciduous woodland in the county of Cambridgeshire,
where it grows in profusion, yet it seems an amenable plant - it grows
in my garden quite happily, but nevertheless shows no sign of taking
over the rest of the country.
Back on the subject, my two Cephalotus are in peat/sand, and will be in
the water tray for Summer. As usual, it is rare for anyone to have the
time or inclination to try lots of different conditions to see which it
actually likes best.