Dr. Edwin Frey in Switzerland grew seeds of the Sanford Citrange and kept only those with non-trifoliate leaves, Sanford is trifoliate.
These non trifoliate leaved seedlings were almost certainly hybrids with true, edible citrus plants where the Sanford Citrange seed plants were located in America.
Growing them on to fruiting has produced some interesting and pretty cold tolerant fruiting plants.
Curafora is one such plant and produces medium sized mandarin type fruits that get quite sweet but are a little bitter still.
The leaves can vary between trifoliate and single on the same plant.
Definitely one for the hardy Citrus testers.