My yuzus are very green since they are harvested in July here, but from what I can find, green is a smell (close to the peel) that reminds me more of the Common mandarin (in the US they call it Willow left). but when it is ripe I will be able to analyze it in more detail, I don't know if you tried that variety to see if you found something similar or it is just an appreciation due to lack of tools to compare.
I have seen once and bought yuzu fruits at a luxury supermarket near where I live. Very surprised to see that. But they most have been picked unripe, because the fruits were much more on the green color side than yellow. I know it certainly was yuzu, but the fruits were very different from the ripe yuzu fruits I have picked off the tree. The skin of the green fruits was much harder and not edible. Whereas the skin of the very ripe yellow-orange fruits was soft tender, similar to citron (
Citrus medica), and the skin is somewhat edible.
I think the best time to pick yuzu is when the fruits are yellow and beginning to become orange, but have not become too orange yellow in color. Before then they have not developed a strong aroma and are very unripe and dry, but after that they start losing sourness and becoming just a little bit insipid, maybe also lose just a tiny bit of aroma.
I realize in different climates, more tropical climates, citrus fruits often remain green and do not turn orange. I do not know how that affects yuzu fruit. But I am saying in other climates, if yuzu is green it is unripe and will not be so good. It will not give you a good idea of what yuzu fruit is supposed to be like.
The peel of yuzu is very important and is where most of the flavor is. It is nothing like an edible kumquat, but if you process the yuzu it has many culinary uses. Think of it like a lemon.
In the longest one it talks about types/populations/subspecies of mandarins, and it seems that a wild population is the closest to Yuzu, the manshangyeju, meaning that the common one would not be its parent. and the seed came from C. ichangensis. It is logical because of the story told in the Riverside collection, where it mentions that it grows wild in China. To my understanding, Ichangensis trees may have been planted near wild populations of these mandarins and only the pollen passed from one flower to the other. This is because ichangensis is used for its aroma in China. (this is just my idea). What is it for us? Well, it could be to repeat the experience and recreate the Yuzu, perhaps using another type of mandarin, as I make many hybrids, I could see what happens,😋. and the other thing is to try to understand that maybe the Yuzu's resistance does not come from Ichangensis... maybe it comes from its Mandarin Parent (from the wild cultivar). and for our hybrids it may be better to use tangerines.
I could not speculate on precisely what the other ancestral parent of yuzu is. But it seems that ichangensis must have crossed with some sort of mandarin orange or sour orange type species. Because the aroma of yuzu has much in common with ichangensis, but whereas ichangensis leans more towards a "pure lemon" citron and lime aroma, yuzu is shifted much more in an "orange" or mandarin orange direction, or perhaps almost fragrant sour orange. Based on the tenderness of the peel, I would have to guess the ancestor is much closer to mandarin orange than orange. The peel of yuzu reminds me most of Satsuma mandarins, but the peel of yuzu is even more tender and less bitter than Satsuma. The genetic studies of yuzu have shown no signs of pomelo (
Citrus maxima) ancestry, but that does not absolutely mean it could not be there.
The hypothesis that the ancestor might have been some sort of more wild sour mandarin species is not an unreasonable one. You can look up
Citrus indica. It might have been something like that. But this is complete speculation, I really do not know.
Then I see if I can make a graph with the visual image and in proportion to what this research says and comparing sizes with the wild mandarin.
The genetic marker studies I have seen on yuzu show very strong dominance of ichangensis in its genes. That means yuzu may not be a direct single generation hybrid, but rather propagated on its own, sexually, and over time the ichangensis genes dominated. I have not seen any genetic studies giving any indication more specifically what type the other ancestor of yuzu might be.
You can consider that, although mandarin oranges are not very cold tolerant, they are usually much more cold tolerant than ordinary sweet orange.
I am thinking it is possible yuzu got some moderate cold tolerant genes from its mandarin orange type ancestor, but almost certainly yuzu must have gotten most of its cold tolerant genes from ichangensis.
Every source I have found says ichangensis is supposed to be much more cold tolerant than yuzu, but my personal experience seems to contradict that.
I have tried growing two ichangensis plants and they were unable to survive here. They went through the first winter but were unable to recover well, which meant they were unable to recover after the second winter. But the yuzu plants I have grown seem to have been more cold tolerant and survived better. Although some of the yuzu plants declined after 2 or 3 years and finally died.
I know with certainty what I grew was ichangensis. I do not know why my experience is different from others. Perhaps it has to do with climate, or perhaps I got a bad ichangensis variety.
I have some Yuzu and a Changsha mandarin plant that appear to be surviving well.
I even tried growing two seedlings that came from an Ichangquat (kumquat x ichangensis) cross, and they finally did not end up surviving outside, seemed less able to survive than Yuzu seedlings I have grown. I am thinking it might not have to do with just actual cold tolerance, it might have to do with vigor and ability to grow after winter. The climate where I am does not get much heat until late June into the year.
Perhaps ichangensis is better in climates that get more heat earlier after winter. I do not know.