I think you may be referring to a kumquat simply known as 'Meiwa', and if I'm wrong, please do correct me before reading further because I will be going on and on about Fortunella crassifolia, or Meiwa!

I have had the cutest little Meiwa kumquat tree for several years now. It is likely a dwarf as it has not grown past 3 feet tall, but it has dark green leaves and plenty of them, and fruits proliferously. Flowers throughout summer, fruit starts growing very quickly and they turn orange by December/January.

Even before the fruits turn orange, I've found that they are already sweet--color can be deceiving! Size tells you a bit more than color when it comes to these kumquats.

I hope this helped! <3

No, Nameiwa is a cross between Nagami and Meiwa, so not a pure Meiwa.

@Martin Weber, oops! Thank you for letting me know that!

In which case, I am so sorry but I have no experience with Nameiwa! I bet you someone here knows far more than I do, though!

I've never seen that either. Where have you heard of it?

Seems to me you take a good tastings fruit such as Meiwa and cross it with a bad tasting fruit such as Nagami. Bad tasting cross.