Salvia Divinorum is a plant closely related to a common ornamental plant grown in many gardens (called salvia officinalis) and is in the mint family. But it's very unique. All of the Salvia D. strains in existence today are quite likely descended from perhaps two plants that were selected hundreds or even thousands of years ago for their psychadelic properties, and grown by the Mazatec people of central Mexico for shamanic ritual purposes. This is the reason you see "salvia cuttings" everywhere. Because it's been cloned for so many generations, it rarely, if ever drops seeds. Let alone seeds that are actually viable and will grow. The Mazatec people cultivate it and eat the leaves (no, they don't smoke them) for spiritual journeys at certain times of the year under special circumstances. The plant was "discovered" (or discovered for science, rather) by ethnobotanist Gordan Wasson. In an ironic twist of fate, nearly all of the Salvia out there is descended from two plants collected at different times. A few rare crops have dropped seeds, creating new strains, but these are not generally available outside of psychadelic circles.
What gets you "high" is not an alkaloid, like most other natural hallucinogens. It's a molecule, plain and simple. And it's structurally different from ever other natural hallucinogen, and the most potent. Only a few synthetic psychadelics (such as LSD-25) are more potent. But make no mistake, it's nothing like LSD, despite the misinformation the media consistently pumps out about it. It's not scientifically understood how it has the effects it does, but obviously it does. And it doesn't get you "high", unless you use miniscule amounts. It can easily be a full blown psychadelic experience when used properly, though it is short in duration. It can be very spiritually or personally beneficial, but for others, a full-blown experience can be absolutely unsettling, and even terrifying for a few. It is unpredictable in nature, and should not be taken by people, in my opinion, that are not informed or are simply using it as a party drug. This is the reason that most other psychadelics are illegal and can no longer be used for research or spiritual purposes, and part of the reason Salvia is quickly becoming prohibited. Irresponsible use by irresponsible people who cannot maturely handle it. If you are planning on using it, just remember set and setting- these things are of the utmost importance, especially since Salvia can cause an instantaneous full-blown disconnection with your environment and even with your ego (sense of self). And yes, there are visual effects from it, as well as the "psychic effects" I just described. Apologies if I sound a bit preachy, but seriously, stupid people constantly screw it up for the rest of us. It is a wonderful plant, and very unique, like I said. It would be a shame to loose the ability to explore it before we even had a chance. Oh, and like virtually every other psychadelic, it's not dangerous, despite what you've been told. I hope that answers your questions, but I'm perfectly happy to try to answer any other specific questions you have. Be well, and be safe.
~Ethno