Orangequat

1/2 mandarin (satsuma), 1/2 kumquat

The Nippon orangequat was described in 1934.  Citrus reticulata x (C. japonica x C. margarita 'Meiwa') 

The flavor is mild with sour pulp. 

The Calamondin is a probable orangequat also.[1] 

There is also a variety named Indio mandarinquat.  The flavor is stronger, edible kumquat type skin, acid interior.

Note the green seeds from kumquat background. Hardiness similar to Satsuma at 12°F, -11°C  Video [2] or 10°F, -12°C[3]