Trifoliate orange (Citrus trifoliata) is an extremely cold hardy citrus tree that produces small, inedible oranges that are filled with seeds. The juice of the trifoliate orange is sour but palatable and can be used for cooking. The tree is extremely thorny and will spread by seeds, including wildlife consumption of seeds. The trifoliate orange is a common citrus rootstock and was originally planted here in East Texas as a living fence for livestock. The tree is extremely cold hardy, surviving temperatures down to below zero.
You can grow trifoliate orange for the juice of the fruit, or you can use it as a rootstock for your own citrus trees. USDA zones 5-10.