There’s a wealth of folklore about the mandrake root—the most common being of its fatal shriek and the typical harvesting method (dog tied to the stalk, that when called pulls out the root and bears the brunt of the scream). (But seriously, check out some of the others—in the Bible, it’s an aphrodisiac; in Germany, the product of hanged man’s seed (and yes, that means exactly what you think it means). Pathfinder’s mandragoras only nauseate, but they’re still nasty little blighters, with poisonous slamming strikes. And since mandragoras are good for spell components and have ties to demons, killing one might be just the start of the adventure.
Wizard Calev Messert has no time for folk superstitions about harvesting mandragoras with dogs—novice adventurers will do just fine. Nor is he troubled if the mandragoras kill some of them in the process—he has no plans to pay them for their troubles, and is already planning instead to poison them and reanimate their corpses as undead.
Execution in Whitemarch comes in three varieties. A simple hanging serves for horse thieves and the like. Knights, gentry, and other important personages languish in jail until the king’s headsman makes his rounds. But truly heinous offenders are left to hang in the gibbet at Carter’s Crossroads. The last man to die there was no man at all, but the tiefling serial killer Barnaby Quicksaw. Now mandragoras fed by his decaying viscera grow in the brambles beneath the gibbet. Due to the rocky soil at Carter’s Crossroads the mandragoras have to struggle to uproot themselves, so the next public display will likely be in full swing when the shrieking plants attack.
King Willowfayeth of the elven nation of Intseneer has been driven nearly mad by the revelation of drow in his sacred woods. Determined to drive them out, he has commanded his alchemists, wizards, and druids (coaxed by a few strategic “disappearances”) to summon demons to harvest for ichor, which in turn yields crop after crop of mandragoras. For a while the mandragoras served as almost living mine fields, but the affair has since turned into a fiasco—the mandragoras are now germinating in the wild, the drow have grown adept at casting deeper darkness to slow the plants, and their raid have freed the summoned dretches to escape into the woods and wreak havoc.
—Pathfinder Bestiary 2 185
As a further note, I’d fully recommend taking that last line of the Bestiary 2 entry—“The newly created mandragora is hostile, even to its creator”—as a suggestion, not Gospel. If it’s better role-playing to have a mandragora hate even its creator, go for it. (For comic relief is one option, or that might be a good way to save a low-level party’s bacon if you need a convincing way to help captured PCs avoid a TPK, for instance). But if you need guards for a mage’s tower and are tired of homunculi, you can do a lot worse than mandragoras.