To take out the location-loaded terms 'native' and 'cultivated', I think what you're trying to ask is, "can hybrids occur between species from different continents"; the answer is yes, provided the species are closely related enough. There are plenty of examples. In Prunus, the hybrid between P. avium (Europe) and P. emarginata (N America) is known, recently named Prunus à pugetensis. I'd doubt that P. serotina could cross with P. avium though, as they are in different sections of the genus (sect. Padus, and sect. Cerasus, respectively). Resin

Consider joining the North American Native Plant Society. Despite the name (it was formerly the Canadian Wildflower Society), it has largely Canadian members and has an annual, by mail, seed exchange for members. Anyone can buy seed (nominal cost to cover mailing) but donors get a special deal. Members across Canada collect seed and mail it to NANPS who then publish a list of available seed. Judy Here is a link that might be useful: NANPS

Bumping this back up to the top of the forum in case there are any new members that would like to sign on. If you are interested, please follow the link and add your name or username ot the list of interested folks. Please do not reply here, use the link and add your name to the correct list. Thanks Barb southern Ontario, CANADA

Apparently it is not fixed, because I went looking for a Native Plant forum to direct a new member to and couldn't find it in the directory. Neither was there a link to it under the only forum about natives that shows up in the directory, the Native Plant Exchange. Another member had to post a link to a thread for it.