Satsuma mandarins may be related to Yuzu

[SoCal2warm]

This is just a hunch but something I've suspected is that Satsuma mandarins may in fact have ancestry from Yuzu.
There are a couple of things that causes me to think this.

Satsuma mandarins are more yellow in hue than the deep orange of other mandarin fruits.

Satsuma shows significantly more cold hardiness than other mandarins.
The only other mandarin types known to be cold hardier than Satsuma are Keraji and Changsha. Keraji is also fairly yellowish in color, and I suspect has heritage from Nansho Daidai (also I believe descended from Yuzu). Changsha is very reddish orange in color and originates from a drier more interior part of China (and as far as I know it was never brought over to Japan) so I believe Changsha is probably separate and does not have anything to do with the origins of Satsuma. Both these two mandarins are not anywhere near the same level of edibility and deliciousness as Satsuma, and the fruit of both are smaller in size as well.

Although the flavor of Satsuma does not have as much tang as other mandarin varieties, there is something in the aroma of Satsuma that is very aromatic and deep, it reminds me of Yuzu. Other mandarin varieties do not really have this quality.

Under the Japanese system, Satsuma-type mandarins are classified in a completely separate family from the other mandarins, though they are all considered to be mikan.
The Satsuma-type mandarin originally came from China, though it later became far more popular in Japan than China.

Just to clear up a little bit of language naming ambiguity, originally "yuzu" was the Chinese name for sour citrus in particular pomelo, but the Japanese took this word and applied it to the citrus now most commonly known as Yuzu (C. junos). The Chinese refered to this citrus as xiang feng (translates as "fragrant orange").
Some of you might note the similarity here to the name "Shangjuan" (fragrant ball). Shangjuan and Xiang yuan are just alternative romanized spellings of the same Chinese word. Among the cold-hardy growing citrus community in America and Europe, Shangjuan has typically refered to the citrus also known as Ichang Lemon (not quite the same citrus as Ichang papeda). However, in China Xiang yuan more commonly refers to the Chinese citron. The Ichang Lemon and Yuzu (C. junos) still exist in China but are very rare, and most Chinese in these regions don't have any knowledge of them. In contrast, Yuzu is well established in traditional Japanese cuisine, and after declining in popularity for a while, has even made a modern comeback in flavored food and beverage products. Most of these citrus were brought over to Japan during the Tang Dynasty (late 7th Century). (The pomelo reached Japan later, from Taiwan, probably since they were only found in the Southernmost parts of China, and weren't as cold hardy as the more mandarin-type fruits)

[Citradia]

Interesting. According to "Hardy Citrus for the Southeast" by McClendon, " Yuzu is an ancient, natural hybrid ( citrus ichangensis x citrus reticulata) that originated in Japan, where it was often used as a rootstock for satsuma ."

[Citradia]

Another reference to McClendon's " Hardy Citrus for the Southeast" : "Changsha Mandarin ( citrus reticulata) is a very old Chinese cultivar. Such plant characteristics as pointed leaf tip, extreme cold hardiness and a skunky odor to the fruit peel point to the possibility that Changsha is a hybrid of some sort with citrus ichangensis."

[SoCal2warm]

Yuzu, Ichang papeda, and Changsha are believed to be closely related, but it's not sure how they are related. I believe it may not be a direct relationship of one being the simple parent of the other.

In general it is usually viewed that Yuzu is a hybrid of Ichang papeda, but I believe it could also be very possible that the two just share the same two ancestors, with differing degrees of heritage. This postulates some original pure papeda species that no longer is found in existence today, with the Ichang papeda coming closest to resembling that original ancestor in morphology. Yuzu appears closer to Ichang papeda than Changsha is, and it's possible Changsha evolved separately, although no one is completely sure.

Yuzu did originate in China in ancient times before it came to Japan. But like many other plants of Chinese origin, it first came to the West by way of Japan. (Another little example, in America we most commonly refer to Tofu by its Japanese name, though on a menu in a Chinese restaurant it's referred to as bean curd). In 1914, the famous U.S. Department of Agriculture researcher Frank Meyer (for whom the "Meyer" lemon is named after) a plant explorer for the USDA, discovered Yuzu growing wild in the southern part of Gansu province in China, among palms, loquats and bamboo. He estimated that the temperatures in that area dipped to 10 F, and no other cultivated citrus grew nearby. Although he originally named it "Kansu orange", he later realized this citrus was identical to the Japanese Yuzu the USDA already had in their collections.

It's just that in China Yuzu appears to have fallen into obscurity, whereas in Japan it became prevalent and valued for bath fragrance and cuisine. There are many possible for reasons for this, all the civil wars in China, and Japan having a more limited variety of different culinary plant species that could grow. Of course now with China rapidly developing and opening up to the rest of the world, the name "Yuzu" is becoming a little problematic since in China the word is now used to refer to pomelo (and even sometimes grapefruit).

[SoCal2warm]

here's my yuzu with fruit on it

[Citradia]

Socalwarm, what's your yuzu grafted on?

[SoCal2warm]

This study looked at DNA markers in Satsuma mandarin, to try to determine its origins, and found it grouped closely with Kishu and Kunenbo mandarins.
(Kunenbo is also thought to be the genetic parent of Kinkoji/Bloomsweet, another cold hardy Japanese citrus)

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5282755/


Apparently what is known as "King mandarin" in the USA, falls within the Kunenbo-type mandarins.

What is known as Kara mandarin seems more similar to an orange, with a slightly grapefruit flavor, and seems to grow very well in Japan handling some frost, it was a cross between Satsuma and King mandarin. It has similar cold hardiness to Satsuma but the fruit requires slightly warmer temperatures to reach full ripeness.