Can you cross pollinate cauliflower and broccoli (outside of genetic engineering)? I honestly cannot say with certainty, but I tend to doubt it. If you can, I would think same species; if you can't, I'd think separate. My supporting evidence is non-scientific and anecdotal - having a garden for 15 years with both plants in close proximity I would have thought if cross pollination had been possible it would have happened in that time frame.
Thank you. From the wiki page, I can't tell if that's Broccoflower is the result of cross-pollination as would happen naturally or the result of direct human intervention - I also can't tell if the seeds from Broccoflower are viable - I'll Google around more and learn :-)
As for overlooking - you're right, I did and should have thought of that before commenting. After a few attempts at saving seeds it became obvious to me that buying them each season was preferable.