Thanks for the reply, Millet, actually these are not flying dragons but anyway it seems some are zygotic. The mother plant looks like standard PT. By the way, it might be an interesting cultivar as the man who sent me the seeds called it an 'edible trifoliate'.
I have flying dragon seedlings too and there are indeed a few off-types among them, dwarfs etc. - probably they're too of zygotic origin.
That's good news, Ilya. I wonder if the presence of long taproot is a genetic trait. If yes, it could be useful in breeding frost-hardy citrus.