Kabosu

Kabosu is a complex natural hybrid of Yuzu and Mandarin trees. Sometimes confused with Sudachi, it has been cultivated since the 18th century on the island of Kyushu, and remains rare even in Japan. Fruits are small, very aromatic limes, to be used while still green for maximum fragrance, from September to November before the first cold weather.
The adult tree has good resistance to cold, and is very productive while maintaining a compact size.

References:
https://citrusvariety.ucr.edu/crc3943