I had no problems bringing roses and succulents back from California last November, and ferns and shrubs back from Kentucky in June. I've brought them in checked baggage, in carry-on baggage, and as a bouquet that I held in my hands. I was afraid of bruising the fern, so it was wrapped in florist paper (like a real bouquet) and hand carried. I did get pulled aside because the scanner picked up the dirt, and I supposed the minerals or moisture in the dirt, but I explained I'm a plant collector and they had no problems. It may have been different had the plane been flying into California, Washington or Oregon, where there are quarantine laws, but the airports I went through had no issues. I do try to bare root plants as much as possible, then wrap in moist paper. It works with the plants I buy--not sure about plumeria.
I have found no rules preventing transportation of plants on any airline. A few times, nurseries have given me inspection stickers, the kind they put on shipping boxes. I've never had anyone ask to see them.
Actually, those were nurseries in California, Oregon and Washington, so maybe the only issues are moving between those 3 states.
