Shikuwasa "Lime"

[Millet]

Shikuwasa lime from Okinawa (actually a mandarin) but is always used as a lime.  I planted a Shikuwasa seed 4 months ago.  The plant is now 7 inches tall and has developed a bloom at the very apical point of the tree. 

[Florian]

I bought some green fruit last year and liked the taste very much, tart/sour but also with a noticeable mandarin note.
My own seed-grown plants have not flowered yet.

Do you know how coldhardy it really is? Reports range from -5 to -15 C..

[deRoode]

There is also a study where shikuwasa was used as a rootstock for inducing early flowering in hybrids.

https://www.sciencedirect.com/science/article/abs/pii/S0304423808000770?via%3Dihub

It is probably a very vigorous variety. I hope to have some seeds this year, and see for myself!