These are some kind of rare cold hardy citrus trifoliate hybrids On the left is a seedling from US 852 (a trifoliate x Changsha mandarin hybrid), on the right is a seedling from Tai-Tri (a taiwanica x trifoliate hybrid) This is a seedling from N1tri (a Citrus ichangensis x trifoliate hybrid) In the lower left corner you can also see the leaves of Citrus ichangensis itself, just for comparison. Changsha mandarin, taiwanica, and Citrus ichangensis are already quite a bit hardier (to zone 8a, approximately) than ordinary citrus, so these hybrids with trifoliate are cold hardier than trifoliate hybrids with regular citrus. All three of these hybrids should be able to survive down to zone 7. These are not something you commonly see. Just an alternative to trifoliate orange that has slightly better fruit quality. US 852 was originally developed as a rootstock.