http://www.sepalms.org/SPS_Hardy_Citrus.htm

Most likely a Satsuma or other cold-hardy hybrid.

If it is large you will have to just live with the tree. It may have froze at one time below the graft or was a seed tree.

ItÂs possible that you have a ponderosa lemon tree. The fruit are very large and I have seen the fruit of this lemon mistaken for oranges.

I agree with Jim, if it is sour, it must have reached below 32 degrees, and you will need to replace the plant. Next time mulch your plants in the winter for protection. I have made the same mistake. Barbra,

You may just have a sour orange. Have you tried cooking with the juice? They also go good in panckaes, etc. I grate mine then cut and peel my oranges and put them in a blender with egg and honey. for orange pancakes. There are always ways of using them oranges. I have put them in the refrigerator and wait about one week and they seem to sweeten up some. My satsuma has that problem sometimes. I wouldn't cut that tree down if you are getting a lot of fruit. They hold up fairly well in the cooler. I have had some last over a month, just have to keep checking. Check with your good local nursery to be sure of the variety. Take a picure of the fruit and leaves with you so they don't have to do too much guessing. If you take the fruit and leaves make sure they are in a zip-lock bag.