Shiranui

The Japanese created this hybrid in the 1970s. In their quest for absolute sweetness, they crossed a Tangor Kyomi and a Mandarin Ponkan.
The resulting fruits are called Dekopon (a protected trademark), but only for the sweetest, with no trace of acidity.
These fruits are large with a typical protrusion, sweet and aromatic with melting pulp. They can be harvested from March onwards, and by keeping them in a cool place for a few weeks they gain even more sugar.

The adult tree remains compact and is fairly resistant to cold.
It is also suitable for greenhouse growing, which means harvesting can be brought forward to late December…

References:
https://idtools.org/tools/1076/index.cfm?packageID=1179&entityID=8814
https://citrusvariety.ucr.edu/crc4249