Weird question, I know. But a friend is searching for the answer. Liriope originated in Asia but appears to have been in the U.S. for a long time (can't find history of introduction). It spreads via rhizomes (roots?!) and does not pollinate or develop seeds. So the "open pollination" criteria does not fit. I have found several articles that note findings of liriope in the wild in selected spots in the SE states of U.S. They appear to have been spread from placed plants and then somehow appeared nearby in woods, etc.
Age of existence is not in question. But I have not found any definition that includes spread by rhizomes. All heirloom definitions refer to seeds--at least those I found. Friend wants to know for a heirloom garden. Obviously would not want to use it if it is truly not considered heirloom. I appreciate any response. I have googled lots and lots so I may be the first to even wonder about this!