What extinct plant inspired the symbol for heart-shaped Valentines?

The shape of the heart is iconic of love, but it barely resembles the organ in our chests that the Greeks called the seat of the emotions. Why is that?

Ancient coins from Cyrene, a city-state where Libya is now, show an impression of a silphium seed; it’s a shape that you know very well. Silphium is the now-extinct “giant fennel” of the genus Ferula. Silphium was the center of ancient Cyrene’s economy because the plant was prized for its medicinal qualities, which ranged from treating coughs to being used as an herbal contraceptive. It was widely used throughout the Mediterranean.

Silphium only grew in the wild and could not be cultivated. Much like the heart it symbolizes, attempts at domesticating the plant may have been the cause of its demise.