"The root known as High John the Conqueror or John the Conqueror root is said to be the root of Ipomoea jalapa, also known as Ipomoea purga, an Ipomoea species related to the morning glory and the sweet potato. The plant is known in some areas as bindweed or jalap root. It has a pleasant, earthy odour, but it is a strong laxative if taken internally. It is not used for this purpose in folk magic; it is instead used as one of the parts of a mojo bag. It is typically used in sexual spells of various sorts and it is also considered lucky for gambling. It is likely that the root acquired its sexual magical reputation because, when dried, it resembles the testicles of a dark-skinned man. Because of this, when it is employed as an amulet, it is important that the root used be whole and unblemished. Dried pieces and chips of the root are used in formulating oils and washes that are used in other sorts of spells."
There are many legends of High John the Conqueror, and here are a few below.
"John the Conqueror was an African prince who was sold as a slave in the Americas. Despite his enslavement, his spirit was never broken and he survived in folklore as a sort of a trickster figure, because of the tricks he played to evade his masters. Joel Chandler Harris's Br'er Rabbit of the Uncle Remus stories is said to be patterned after High John the Conqueror. Zora Neale Hurston wrote of his adventures ("High John de Conquer") in her collection of folklore, The Sanctified Church.
In one traditional John the Conqueror story told by Virginia Hamilton, and probably based on "Jean, the Soldier, and Eulalie, the Devil's Daughter", John falls in love with the Devil's daughter. The Devil sets John a number of impossible tasks: he must clear sixty acres (25 ha) of land in half a day, and then sow it with corn and reap it in the other half a day. The Devil's daughter furnishes John with a magical axe and plow that get these impossible tasks done, but warns John that her father the Devil means to kill him even if he performs them. John and the Devil's daughter steal the Devil's own horses; the Devil pursues them, but they escape his clutches by shape-shifting.
In "High John De Conquer", Zora Neale Hurston reports that like King Arthur of England, he has served his people. And, like King Arthur, he is not dead. He waits to return when his people shall call him again ... High John de Conquer went back to Africa, but he left his power here, and placed his American dwelling in the root of a certain plant. Only possess that root, and he can be summoned at any time.
This is from Hurston's published article in American Mercury magazine in 1943. In this article she relates a few stories about High John, enough to define him, but not an exhaustive survey of the folklore. The purpose was to present the nation with the hope-building and the power of this inspiring figure during the darkest days of World War II. The article ends with:
So the brother in black offers to these United States the source of courage that endures, and laughter. High John de Conquer. If the news from overseas reads bad, if the nation inside seems like it is stuck in the Tar Baby, listen hard, and you will hear High John de Conquer treading on his singing-drum. You will know then, that no matter how bad things look now, it will be worse for those who seek to oppress us.... White America, take a laugh from out of our black mouths, and win! We give you High John de Conquer. (The American Mercury, October 1943, pp. 450-458)