Several months ago a small (15mm) Greek bronze coin came my way that has resisted identification until now (thanks to Dane Kurth). It turns out is a coin from Cyrene in Cyrenaica with the helmeted head of Athena on one side while on the other are two stalks of the silphium plant emerging from a single base (BMC Cyrene 202-3).
It is, for me, the silphium plant that is of interest. The exact identity of silphium is unclear. It is commonly believed to be a now-extinct plant of the genus Ferula, perhaps a variety of giant fennel. It was used in classical antiquity as a rich seasoning and also as a medicine. It was the essential item of trade from the ancient North African city of Cyrene, and was so critical to the Cyrenian economy that most of their coins bore a picture of the plant. The valuable product was the plant's resin.
Many medical uses were ascribed to the plant. It was said that it could be used to treat cough, sore throat, fever, indigestion, aches and pains, warts, and all kinds of maladies. It has been speculated that the plant may also have functioned as a contraceptive, based partly on Pliny's statement that it could be used "to promote the menstrual discharge". Many species in the parsley family have estrogenic properties, and some, such as wild carrot, have been found to work as abortifacients (chemicals that terminate a pregnancy). Given this, it is quite possible that the plant was pharmacologically active in the prevention or termination of pregnancy.
The cause of silphium's extinction is not entirely known. Overgrazing combined with overharvesting may have led to its extinction. It may be that when Roman provincial governors took over power from Greek colonists they over-farmed silphium and rendered the soil unable to yield the type that was said to be of such medicinal value. Theophrastus reports that the type of ferula specifically referred to as "silphium" was odd in that it grew only in the wild and could not be successfully grown as a crop in tilled soil. Pliny reported that the last known stalk of silphium found in Cyrenaica was given to the Emperor Nero "as a curiosity".