Mandrake Root

Mandrake Root (MR) is a magical reagent used frequently in traditional Britannian and  Serpent Islander magical practices, and also features prominently in a number of occult practices on Earth. Known to Terran botanists as mandragora, these plants are noted for the humanoid shape of their bifurcated root systems, and many varieties contain hallucinogenic alkaloids which have likely contributed to their notoriety as a witch's staple.

Britannia
In Britannian magic, the portion of the mandrake which is employed is the fibrous portion of its tap-root, which must be removed from the plant with a silver utensil, boiled in purified water, and dried before being put to use ritually. Once thus prepared, the mandrake will lend potency to spells which require it, acting as a magical enhancer of the energies invoked by other reagents. Due, no doubt, to its obvious value in weaving powerful magics, the mandrake was for many years a rarity in the Britannian landscape, appearing only in damp swampy regions such as the Bloody Plains and the Fens of the Dead.

Serpent Isle
Given modern Serpent Islanders' common Sosarian origins with Britannia, it is unsuprising that mandrakes function near identically within this cold world's magical traditions. However, unlike Britannian mages, Serpent Islanders also employ fresh mandrakes for their unique magical properties, which apparently differ from those of the dried compound. Such roots are necessary, for example, in the creation of individualized spellbooks by the Moonshadians.

Earth
On Earth, mandrakes (part of the Nightshade family) have long featured as aphrodisiacs and narcotics in both witchcraft and archaic medicine, and have developed a number of legends regarding their origins and harvest. Often said to only grow where the semen of a hanged man has fallen to the earth, mandrakes are said in many myths to issue a scream when pulled from the ground - the sound of which is sometimes said to bring death to all who hear it. Owing to such superstitions, mandrakes were at one time traditionally harvested by tying a dog or other expendable creature to the plant in question, such as that the gatherer could get a safe distance away before the root was unearthed. 

Trivia

 * In the Nintendo port of Ultima IV, the play may, in fact, buy "Manroot" at apothecary shops by pressing the "SELECT" button while selecting their purchase.
 * In Yoko Tanaka's manga re-telling of Ultima IV, the Deane and his party members must at one point gather a total of fifty mandrakes that they might convince  Mariah to join them. They are assisted in the endeavor by Deane's former tutor, Calumny, who explains in detail how to harvest the reagents without killing the tiny humanoid plants which produce them. In this narrative, mandrakes are shown as screaming plants, much as they appear in Terran mythology, although the sound of a mandrake's wail is merely irritating and is not lethal.