Silphium

Silphium is a plant native to Shade, widely used in cooking and medicinally. Particularly, it acts as a natural, very effective, contraceptive/abortifacient.

Silphium is notoriously difficult to grow because it demands exact conditions, and as a result it only grows in very restricted regions. The only area that produces it in large proportions is Quetchia. It has so far resisted attempts to cultivate it artificially.

This fictionalised silphium is based on the reported properties of a real (extinct) plant of earthen antiquity. It may not resemble it exactly in appearance. See [silphium on Wikipedia] and this [article from The Straight Dope].