UF/IFAS Trial 3 records UFR-11 as a sexual cross with Sanford sweet orange as the seed parent and Argentine Trifoliate as the pollen parent.
Source [1]: https://crec.ifas.ufl.edu/media/crecifasufledu/citrus-research/images/rootstock-trials/indian-river-marsh-grapefruit/Trial3_updated_10_21.pdf