Contrary to popular belief, the orange and the lemon have not always been around. According to botanists, the four original citrus fruits are the esrog, pomelo, mandarin, and papeda. All of the citrus fruits we have today are hybrids of these four fruits! The lemon is a hybrid of the citron, mandarin, and papeda — with most of the genome coming from the esrog. The orange and grapefruit are closely related to the mandarin orange and the pomelo. The lime, which most think is a lemon hybrid, is actually the offspring of a papeda and esrog.
There have been numerous archeological finds with pictures of the esrog on them. The earliest being from Egypt, 3000 years ago. A coin was also found from the Bar Kochba period, with all four minim embossed on it. Interestingly, there was only one hadas and one aravah on the coin, the opinion of Rabbi Akiva, whom Bar Kochba followed.
The esrog tree is a very weak and short-lived tree. Without constant water, support and care it will not survive the 10-15 years it is expected to live. In order to strengthen it and elongate its life, many graft its branch to the lemon tree. This has caused the purity of different esrogs to be questioned, and many Halachic authorities rule that only pure esrogs can be used as one of the four minim.
In Rome the citron was known as the mala Medica or the “Persian (Median) apple”.
In Europe the climate caused the Jewish population to face esrog shortages. Only the temperate climate of the Mediterranean Basin was fit for the esrog trees to grow properly. This caused countless hardships to procure the esrog for Succos, to the extent that by some accounts there was one esrog for an entire town. In the 18th century, Jews living in Bohemia were taxed 40,000 florins (which in todays currency is approximately a million dollars!) in order to be able to import esrogim.
In ancient Greece, the esrog was used for its medicinal properties; helping ward off seasickness, intestinal issues and other ailments. In modern times, it is still used in many holistic approaches to treat nausea and vomiting.