Ethrog or Citron

Here's a nice post about the citron, not one of the more popular, well-known, or useful of citrus fruits.  At times it's tough to know what fruit or plant ancient texts are referencing, but if you like this sort of thing, you might see if you can round up a copy of Michael Zohary's Plants of the Bible published about 30 years ago, or a number of other similar books.