Quite an interesting article

'the differences in the flavour notes and other characteristics of coffee varieties from around the world are not down to variations in individual genes, a study has found. Rather, they seem to be mainly the result of wholesale swapping, deletion and rearrangement of chromosomes.'

And

'Most genetic variation in living organisms comes from hybridization with other species. However, that is a relatively rare event for C. arabica because it has more than two copies of each chromosome — a phenomenon called polyploidy. Coffea canephora has two copies of each chromosome, but C. arabica contains multiple copies. This makes it much more difficult for arabica to interbreed with other species.'