Sooo much information you have not given us; but first glance would be Bearss lime... what does the inside look like?
Looks like a serious spider mite problem..

OK. Here's a picture of the flower, and in the next post I will show what the inside of the fruit looks like.

Here is the fruit cut open. I'm not sure what other details to give; the tree is really tall, like over 10 feet tall I think. It was planted before I got here in the backyard of our rental property so I don't know any other details.

We are in San Francisco, so the climate gets foggy and cool during the summer, but during the non summer months on nice days the spot gets a ton of sun, and we really don't get a lot of rain except for during the winter months.

I will show a picture of the thorns in the next picture.

Finally, here are the thorns. Let me know what other details I can supply and I will do my best. Thanks all!

Looks like a lemon; maybe a Eureka. I think it is far from ripe; probably will get ripe.. and yellow, around late November. Leave them be; and they will get larger; and the skin will get thinner; and if you post a photo when they get yellow, with the fruit cut in the opposite way (equator of the fruit), someone here will probably be able to tell you for sure what it is.

Looks like citrumelo to me (which for us here in Californai is Swingle rootstock, a commonly used standard-sized rootstock many citrus are grafted to here in California). Doubtful you have anything edible. Not a lemon, not Eureka lemon for sure. Can you see if your tree has a graft line on the trunk, or does it look like perhaps this tree's grafted cultivar has long since died, and we're just dealing with the rootstock taking over.

Patty S.

Looks like citrumelo to me (which for us here in Californai is Swingle rootstock, a commonly used standard-sized rootstock many citrus are grafted to here in California). Doubtful you have anything edible. Not a lemon, not Eureka lemon for sure. Can you see if your tree has a graft line on the trunk, or does it look like perhaps this tree's grafted cultivar has long since died, and we're just dealing with the rootstock taking over.

Patty S.

Patty is undoubtedly correct; I had not even considered that it was a rootstock.
Always best to take advice from local experts.

Awesome - thank you guys! I will go and look for the graft line. And thanks for the tip on cutting it the more correct way in terms of helping to identify!

It looks I have same tree... Bought it from a Flea Market and it was labeled as Calamansi tree but now it has a fruit that looks like the ones you have pictured.. so have you found out what it is? Thanks

Probably won't get an answer, the thread is 8 years old.