On the Origin of Species: Oddish
It's a strange, walking plant that hides underground in the daytime, its feet disguised as roots. At night, the moonlight prompts it to wander around... but if you try to pull it out of the ground by force, you're liable to get screamed at. You'd be forgiven for thinking that Oddish is too odd to be based on anything real. As it happens, though, Oddish is indeed based on an actual plant, albeit one that's been steeped in myth for thousands of years.
The plant in question is the mandrake: any one of the species belonging to the genus Mandragora. Mandrakes have large, oddly-shaped roots, grow small, tomato-like berries in the spring, and are very poisonous. They produce a class of chemicals called anticholinergics, which interfere with the nervous systems of humans and other animals. Indeed, the most powerful anticholinergics known to exist actually come from mandrakes. The plants most likely evolved these chemicals as a defense against being eaten, but in sufficiently small quantities, they can be used for medicinal purposes. They're used to treat a wide range of conditions from asthma to Parkinson's disease, while in ancient times they were mostly used as a form of anesthetic, since disrupting the activity of the nervous system does have the effect of numbing pain. Pliny the Elder (23-79 AD) and Dioscorides (40-90 AD) both noted the use of mandrake extracts as painkillers, while the Bible (in Genesis 30) mentions them as a cure for infertility.
And it's to ancient times we must go, to get to the root (if you'll pardon the pun) of the mysterious properties that have been ascribed to the mandrake. Now, in the days when medicine and magic were all but the same vocation, it wasn't unusual for plants that were poisonous, or medically useful, or both, to be thought of as magical in some way. In addition, the chemicals produced by mandrakes can be hallucinogenic, and in a time when hallucinations and their causes weren't understood, these too would be considered to be the effects of magic. Despite the use of mandrakes in the Bible itself, the medieval Church ultimately frowned upon possession of something so closely associated with magic and witchcraft: in 1431, this was actually one of the charges that led to Joan of Arc being burned as a witch. So, we already have some evidence that past cultures considered the mandrake to be a special, magical plant... but its chemical properties are just the tip of the iceberg.
Appearance counts, and it's the mandrake's unusual appearance that seems to have made it so mythologically significant. Mandrake roots are very thick and are often forked in a way that makes them resemble a human torso and legs. This similarity led to myths that mandrakes didn't just look like people; they were people... at least, of a sort.
The myths varied and became greatly embellished over the years, but a few features came up time and time again. Mandrakes were said to be connected with dark spirits of the earth, and so had to be handled with extreme caution. Uprooting a mandrake was fraught with danger: it could only be pulled from the ground by the light of the moon, and even then, the act was liable to kill whoever uprooted it. Because of this, many alchemists' guides recommended tying the plant to a dog, and getting the dog to do it instead. The dog would be killed, but once uprooted, the plant could be used safely. Other versions of the myth – which are referenced in the Harry Potter franchise among many others – state that a mandrake would scream at anybody trying to uproot it, and this scream could be fatal if precautions weren't made to protect the ears. As silly as all of this sounds, most myths have some sort of basis in reality, and we should bear in mind that mandrakes are very poisonous. Anyone who uprooted one with the intention of consuming it was quite likely to end up dead, and so we can see how these stories might have developed.
In medieval times, it seems that many scientists weren't sure whether to treat mandrakes as plants or as animals, and they seem to have been regarded as both. A similar situation occurred with cotton: when imported cotton first arrived in Europe, people struggled to believe that the wool-like substance could have been harvested from a plant, and so cotton plants were depicted as strange half-plant, half-sheep hybrids. Likewise, one popular view of mandrakes was that they represented a sort of intermediate stage between plants and humans.
The idea of mandrakes as semi-human actually continued, in the minds of some observers, up until the nineteenth century. In his 1855 book, Dogme et Rituel de la Haute Magie (Dogma and Ritual of High Magic), the French occultist Eliphas Lévi seemed to be trying to tie the mandrake myth in with the scientific community's changing ideas about the origin of humans:
"Is this root the umbilical vestige of our terrestrial origin? We dare not seriously affirm it, but all the same it is certain that man came out of the slime of the earth, and his first appearance must have been in the form of a rough sketch. The analogies of nature make this notion necessarily admissible, at least as a possibility. The first men were, in this case, a family of gigantic, sensitive mandragores (mandrakes), animated by the sun, who rooted themselves up from the earth..."
Oddish really does take a surprising amount from these myths: its shrieking, its association with moonlight, its legs being roots... even its color seems to have been inspired by old depictions of mandrakes. It's an intriguing nod to a plant that has probably inspired more myths and strange tales than any other.