A couple of years ago, I got some seeds of mandarinquat (mandarin X kumquat?). I have kept a single seedling (the most vigorous one). Initially I did not pay attention to the fact that it's leaves are pretty different form both parents:



From left to right: mandarin-mandarinquat(?)-kumquat.

But later I started wonder why the petioles of the mandarinquat are winged while the petioles of both parents are not. Could this indicate that what I've got, actually is not a mandarinquat?
Harri.

The Indio mandarinquat is reported as variable from seed, not sure about others. The fact that the petiole wing is bigger in the " hybrid " would not be unexpected. If you grew seed from a mandarinquat, you probably have a second generation hybrid, assuming it wasn't cross pollinated.
You should be able to find characteristics of both parents in your plant.

The long and winged petioles puzzle me, they must be due to some species other than mandarin and kumquat in the parentage. Or do I mistake? And I did choose the most typical leaf for picture...

Do you remember if there were other seedlings coming from the same seed?

I checked with my Kugle, that is supposed to be also mandarinequat, petioles are long, but wing is not very characteristic.

If your seedlings is monozygotic, it could come by cross pollination with something like grapefruit.
On the other hand leaves of young plants are very often non typical, may be you need to wait for some more time.

If I don't mistake, this seedling was the one and only from this seed... I indeed do not have any other choice than to wait and look what kind of fruits this hybrid will bear finally. It's two years old by now and the leaf presented is very typical. The very first true leaves of it were smaller and with petioles shorter and less winged. But, of course, the plant is not mature yet and the leaves may change in the coming years.