Keraji is a cold hardy Japanese mandarin with yellow-orange skin. The taste is like lemonade and the fruits are small and a bit seedy. Supposedly keraji can handle down to 12 °F.
One tree was growing outside unprotected and fruiting in Virginia Beach.
Apparently it was a fairly popular tree in the Southeast among those growing cold hardy citrus, but I can't seem to find any nurseries carrying it now.
A nursery owner in Georgia was kind enough to send me seeds
During my research I came across something interesting in a Japanese genetic analysis paper. Seems like keraji shares in common a parent with satsuma mandarin, a type of Japanese tangor called kunenbo which must be confering a degree of exceptional cold hardiness (it's a parent of bloomsweet as well). The analysis actually indicated keraji was probably a backcross of kunenbo with another sour-type citrus known as kubachi (today rather obscure, but the pictures I was able to find look similar to kabosu or sudachi).
I just read another research paper DNA analysis that says keraji appears to be a cross between kunenbo (seed parent) and kikai-mikan. I found a picture of kikai-mikan and not surprisingly the fruit looks a lot like a cross between both the pictures of kubachi and kunenbo I saw. So it looks like keraji may indeed be a backcross with kunenbo—that is (kubachi x kunenbo) x kunenbo.
For any of you who may be interested, here's the picture of kikaimikan (喜界みかん) I was able to find:
And here's here's a Japanese site showing pictures and description of Kunenbo:
http://www.michinosima.com/kaimono/kunenbo.htmlThe name Kunenbo translates as "nine year mother". The fruits appear pretty similar to a Kara mandarin. (One of Kara's parents is Satsuma, and Satsuma is a Kunenbo cross with Kishu. Kara is also pretty cold hardy and grows in frosty areas of Japan. Maybe that's giving too much information here)
I suspect there might be different cultivars of keraji as well, with slightly different qualities when it comes to edibility/flavor, if these plants have been propagated at some point from seed. The seeds seemed pretty big like they would be really easy to grow, so that may be likely.
Well that's pretty funny, I start a thread about keraji and show you pictures of its entire lineage of obscure parents but don't show you a picture of keraji itself. Well, there are plenty of pictures of keraji mandarin on the internet so you don't need me to post that there.