Planted this from a nursery labeled "mandarin orange". I'm guessing that the orange branch had been grafted onto something else and died. Maybe ornamental fruit? Definitely not edible... Has been giving fruit for a few years now. Smells a little like a lemon only EXTREMELY bitter -- so bitter you can't even taste a little without brushing teeth.

Original thought it was some exotic disease, but the tree/leaves don't show any of the symptoms for those diseases.

Any ideas what it could be?

Fruit on tree
http://imageshack.us/a/img545/7436/gwaq.jpg

Fruit on tree 2
http://imageshack.us/a/img853/2371/7bgs.jpg

Inside fruit
http://imageshack.us/a/img196/2043/d2qa.jpg

Leaves
http://imageshack.us/a/img202/6913/h3tg.jpg

Leaves #2
http://imageshack.us/a/img202/7117/2psb.jpg

Limbs
http://imageshack.us/a/img440/1470/wszj.jpg

Trunk
http://imageshack.us/a/img855/5581/xonb.jpg