Is this tree deciduous? Trifoliate orange is pretty much an orange--it's in the citrus family. Poncirus is the "hardy" orange and loses leaves come winter. It's hardy to zone 6...the Kei apple is another good candidate. It is evergreen, so that's why I asked if the tree loses its leaves in the winter...
I think trifoliate orange is more a lime or lemon, like kefir is, in my humble opinion. I don't know where it got the orange in the name.
Their position on the citrus family tree is a matter of debate; they don't seem to hybridize very well, and their genetic make up differs a whole lot from most wild citruses found in the world. Some types of citrus can't even be grafted on them due to those differences.
Some scientists think their diversion from the citrus genetic branch has been too long ago and it's a "new" family.
Too bad because they're the toughest citrus plants I know. Easy to propagate too! Leafless branches root in a blink.
I've been trying to work with both the flying dragon as well as the main type, to get some hardy rootstock and see if that hardiness is tranferrable. But I haven't been succesful in the past five years.. Mostly due to a lack of skill I hope.