Hybridisation of Fingerlimes dates back about 100 years.
Citrus virgata, the Sydney Hybrid probably originated from close planting of C. australasica Finger Lime and C.australis Round Lime at the Sydney Botanic Garden ??
The two species don't converge in the wild, even though they are found not so far apart, maybe 70 km or less.
The Faustrimedin dates back to 1911, a hybrid between Microcitrus australasica and Calamondin.
The Eremolemon dates back to at least the 1920's. Eremocitrus X Myer is supposed for that one.
The Faustrime, Microcitrus australasica X limequat is probably from about the same period.
That was just about it for a while, possibly until the Blood Lime and Sunrise Lime were developed in the early 80's.
Some European '' Finger Limes" are clearly hybrids, judging from their odd shaped fruit or robust foliage.
Saga University in Japan also bred a lot of Microcitrus X Microcitrus and Microcitrus X Citrus hybrids.
If anyone can add to this list, that would be great.