Citron
A source of confusion is that "citron" or similar words in French (and other languages), and English are false friends, as they refer to the lemon. Indeed, into the 16th century, the English name "citron" included the lemon and perhaps the lime as well.
Ponderosa lemon
Ponderosa lemon is less cold hardy than a true lemon. It bears medium to large fruit that have a thick and bumpy rind. The fruits are seedy, and while they look similar to a citron, they taste like a lemon.