Sour Orange Canaliculata or Striata
This is a bittersweet sour orange with a most unusual fruit.
The flesh is often sweet when ripe but the pith is very bitter.
The fruit is easily distinguished from other sour oranges because it is ribbed vertically.
This is an ancient variety seen in some of those old Italian citrus paintings from around Leonardo Da Vinci's time.
Quite a cold tolerant tree so another one for those hardy citrus experimenters.