DND, now you have me all worked up!! What I know about gardening, you could fit in a fly's come si chiama, but research is more in my wheelhouse.
I can't help but think that something might open up for you if you researched the family, not having all the sources be garden-related. You could find people who had some contact with the family who have these daylilies in their gardens and don't think anything of it. You never know what family and family friends know or have.
I'm still not allowed to post links, you'd think they'd know by now I'm not a bot with a way to make a million dollars a month at home in my spare time, so let me try this: http:// static.clarionledger.com/contact/ -- one is the contact page of the newspaper in Jackson, the Clarion Ledger. They could very well be interested in your search, and if they do an article on it, that would do a lot of your legwork for you. At the very least, you could ask them to search their morgue for mentions of the family. Contact the newsroom, tell them you want to talk to features, and tell them what you're up to.
I've also gotten the contact info for the Archdiocese of Jackson. If someone is French, they could very well be Catholic, and those ties run long and deep even when people aren't serious or devout, especially if they're based in a town where the Archdiocese is located. They could at least help you with records of births, deaths, marriages, good way to find surviving relatives. http:// jacksondiocese.org/contact
And that site in French? Post in English, people in Europe speak multiple languages and don't get sentimental about it, and English, for now, is the language of commerce, so people who don't have it as a primary language, get it.
I don't want to annoy you, but this is how my brain works, I've worked as a journalist.
