Oranges and lemons on the same tree - so it's a multi-grafted tree? Is it possible that the lemons are rough lemons (growing from the rootstock)? The rind doesn't look discolored like you would expect if the bumpiness was due to fungus or insect damage.

I've also read that grapefruits can get bumpy skin from over-watering, but I don't know if that affects lemons. Maybe some lemon experts can chime in.

Assuming that the insides look normal, I don't see why the fruit wouldn't be safe to use - at least the insides.

If I threw out every ugly fruit from my mandarin orange tree, I'd lose most of the crop. A lot of my mandarins have puffy skin. I kind of like it, though. They may be ugly, but it makes them even easier to peel. :-) They also seem to take more cold before the inside of the fruit gets freeze-damaged. I guess the air layer between the skin and the fruit acts like insulation.

Did it just start producing such fruit, or was the fruit always a little weird? It might be that there are some citron, sour orange, or other genes in there that caused it. It might be inconsistant watering. Or maybe Neptune was in alignment with Orion and the chakras didn't jive, sometimes things just happen. Try it and if it tastes fine, it probably is.

My neighbor doesn't feed, use pesticides, or water any of her trees, they always fruit profusely. I have never seen any lemons on this tree before though my neighbor seemed unsurprised so she must have known about them. She has been sharing the oranges with me for years but this is the first time they have had these lumps and bumps on them.
I have just cut both fruits open. They look fine inside, if a little past their harvest time, as the lemon especially looks dry. The orange smells slightly of tangerine. The flavor has never been especially strong or sweet.

Watering would be a good idea. They don't always need it in Florida, but if one ~10' tree is producing >5 pounds, it might be worth trying. Or again, it might be netune, Orion, and the chakras.

I'll bet it's a rough lemon growing from below the graft. I saw them in a citrus nursery many years ago where they were grown for seedling rootstock. I can remember that from over 50 years ago, but I don't recall what I had for breakfast. :o)
john

Thanks guys! I think you may be right about the rough lemons. I had never heard of them before but I took a quick look at the tree and the branches with the lemons on them seem to be growing from a separate 'trunk' from ground level. Are they grafted to the actual root, below ground? I'll try to get a better look at it tomorrow and perhaps post one or two more photos. If they are in fact rough lemons I am going to have to break the news to my neighbor!
Just one puzzling fact though, why do you think the oranges have now started to develop these lumps and bumps? They never had them before!

The rough lemon IS the rootstock to which the orange bud is grafted, Some times the root stock puts out a shoot that will eventually bear fruit. If a citrus tree gets frozen it will likely come back from the rootstock.
john

John - the key to remembering what you had for breakfast, is to always have the same thing. Just had to add that, I know nothing at all about ugly lemons. Jen