USDA Circular 181 (1931, printed p. 4) says the original hybrid records were lost, grapefruit was the known seed parent, and the pollen parent was not definitely known. The authors infer tangerine character from sister hybrids. “Mandarin (presumed)” is therefore a broad pedigree-group inference, not an identified pollen parent. The existing 50/50 ancestry is a pedigree estimate, not a measured genomic proportion.
Source [5]: https://upload.wikimedia.org/wikipedia/commons/5/58/New_citrus_hybrids_%28IA_newcitrushybrids181walt%29.pdf
Revision: Qualify the existing broad pollen-parent group with USDA Circular 181’s explicit uncertainty while preserving the known grapefruit seed-parent group and relationship structure.
World of Citrus