Very interesting, Keith!
Appreciate being forced to think.
I guess the answer is: not naturally, but hybrids can be produced by means of tissue culture (e.g. the"gonion"). I'm assuming, however, that the gonion is sterile.
Apparently, interspecific hybridization, typically associated with polyploidy (viz with an increase in the number of sets of chromosomes) has been an important mechanism in the (natural) evolution of plant species.
