Hystrix has nothing to do with sour orange.
It is a species apart with close relation to micrantha.
I believe C. hystrix originated from hybridization between C. latipes and some sort of sour orange (likely within the C. aurantium group).
It is a species apart with close relation to micrantha.
You are in error.
Regular limes have close relation to micrantha. Kaffir lime is in a different group from regular limes.
(C. micrantha and C. latipes though are closely related species, but they are original separate species)
This is just from my memory, and I can't seem to find a source to substantiate this right now.
I suppose it could be possible I am wrong, and not remembering correctly.
I am able to find the following sources of evidence:
entry for C. latipes [Khasi papeda]
A plant much similar to C. hystrix in the habit, leaf, floral and fruit characters.
There are no striking differences, except that C. latipes has comparatively smaller leaves and fruits, and more number of seeds (30-60 per fruit) than in C. hystrix.
C. latipes is native to North East India (Meghalaya: Khasi and Garo Hills; Nagaland) and Northern Myanmar.
Indian Ethnobotany: Emerging Trends, Jain, A. K., p257
I think measured furanocoumarin levels also support the idea that C. hystrix likely did not descend from C. micrantha.
Here you can see in this study, that looked at different types of furanocoumarin levels, that Kaffir lime (listed as its synonym Rangpur lime) did not even group with the C. micrantha admixture group including regular limes:
https://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0142757&type=printable(The Distribution of Coumarins and Furanocoumarins in Citrus Species Closely Matches Citrus Phylogeny and Reflects the Organization of Biosynthetic Pathways, Audray Dugrand-Judek)
The levels in both Khasi papeda and Rangpur lime are extremely low, while the levels in other limes are very high, and the levels in C. micrantha are extremely high, higher than any other citrus by a large margin.
The level of cold hardiness also suggests Kaffir lime has more in common with C. latipes than C. micrantha.
However, I am also looking at another study which seems to group C. hystrix first closest to C. macroptera, then to C. micrantha, and then to C. latipes, in that order.
( Nicolosi E., Deng Z., Gentile A., La Malfa S., Continella G., Tribulato E. Citrus phylogeny and genetic origin of important species as investigated by molecular markers. Theor Appl Genet. 2000;100:1155–1166. )
cpDNA seems to inexplicably group C. latipes much closer to traditional citrus so it's possible there could have been introgression into the C. latipes gene pool, which could explain why it doesn't group closer, but maybe that theory is a stretch of an explanation.
(What I mean is maybe C. hystrix descended from a more pure C. latipes that existed in the past, and the C. latipes accession that exists today are not as pure)
If you look in the graph in Figure 3 of this study you can see that, unlike other limes, Rangpur lime does not seem to have any relation to C. micrantha.
Phylogenetic origin of limes and lemons revealed by cytoplasmic and nuclear markers, Franck Curk Frédérique Ollitrault Andres Garcia-Lor François Luro Luis Navarro Patrick Ollitrault, Annals of Botany, Volume 117, Issue 4, 1 April 2016, Pages 565–583
(it's the smaller bar graph in the middle, fourth from last)
The Encyclopedia Britannica has this entry:
"The mandarin lime, also known as the Rangpur lime (C. ×limonia), is thought to be a lemon–mandarin orange hybrid..."
https://webcache.googleusercontent.com/search?q=cache:QhSA4vLf7RUJ:https://www.britannica.com/plant/lime+&cd=19&hl=en&ct=clnk&gl=us