I was given a blood orange tree as a gift, but I'm not sure which cultivar it is. It's fruit is oblate (flattened) like a vidalia onion. Any ideas? Thanks

Jack,
Do you have pics of it, including the cut-up sections? None of my collection of blood oranges are oblate or flat. Some are only very slightly flat. Perhaps you have a blood sport of mandarins or maybe pigmented tangelo.
Joe

but it is almost shaped like a tangerine. I'll know for sure when it ripens.

tangerines are technically grouped under mandarins, and perhaps they could have blood sport mutation also. IIRC, I come across discussion of tangerines or mandarins, and some have mentioned about the pigmented mutations. These are not yet publicly available from the UCR budwood program, and if it were, it will surely be on my tree. The major restriction that I have is I cannot get budwood outside of our region although I can send them to most states without problems.

Joe did you notice the number of your post above -- a straight line post. Number 1234 - Millet

I would cut one up for you now. When it ripens I'll get you those pics. It had two other oranges growing on it this summer, but they split open and I pulled them off. Maybe it was just mislabeled at the nursery. We'll see.

sour and sweet? The "blood orange" I received as a gift appears to be something else. I checked the hand-written label again. It said "blood orange" on one side, and "citrus aurantium sinensis" on the other. Now I'm really confused. By searching "citurs aurantium" I found lots of pics from German websites that closely resemble my orange. Is it a sour seville orange? Is it worth keeping? Thanks.

Seville oranges while flat, are not as flat as mandarins, so there is a chance that seville orange it is not.

Citrus aurantium is indeed a sour orange. Citrus sinensis is a sweet orange... Looks like you are going to have to wait until the fruit ripens.

Show us a photo of the tree. There are some pretty good people
in this thread that probably can identify what you have by the
looks of the tree and the fruit. Now, with the label in mind,
let's see if this tree was grafted or not before we go too much
further. I can say this much, it is not uncommon that a Moro
Blood Orange can have a flat base to the fruit on young trees,
especially when there are possibly too many fruit on the tree
or from the first few fruits the tree produces when young.

Snickles

one side of the tag labeled "blood orange" the other "citrus aurantium sinensis". It was soft to the touch so I picked it. Lets' hope that link works. It wasn't blood red or sour. It was just a tangerine mislabled. This one was from Florida, but TyTy has done this to me before. At least it tasted nice.

bummer! I was hoping to see a blood sport of tangerine or mandarin...

Just enjoy!