A very instructive article on the process of mandarin diversification and domestication has been published recently
Genome of Wild Mandarin and Domestication History of MandarinThey found a center of radiance of Citrus reticulata in Nanling mountains in South China, sequenced the genome of two wild plants in Mangshan region and used this information and previously developed markers of pomelo, C.ichangensis and citron to identify two groups of domesticated mandarins North and South of Nanling ridge.
Domesticated mandarins show a dramatic decrease in fruit citric acid content, while their sugar levels are not different from wild plants.
Mangshan mandarin ( different from Citrus mangshanensis also growing in this region) has already 1.7% of its genome introgressed from Ichang papeda, but almost no influence from pomelo or citron, while domesticated mandarins have up to 10% percent of genes from pomelo.
Satsumas are very different from both groups of Chinese mandarins and have 27% of introgressed pomelo, more than clementines with 18% of pomelo genes.
Mediterranean mandarin belongs to the South group of Chinese mandarins, while Changsha and Ponkan are North mandarins.