I'm pretty sure I've never mentioned it on the site, and I'm not going to go through 140+ posts to check, but I have a degree in alternative medicine. Note I am not a hippie, if you have a serious mental or physical ailment go to a qualified conventional doctor and get diagnosed and treated, alternative medicine is all about being minimally invasive and this is a limiting factor, when used in conjunction with traditional medicine alternative techniques can assist the body in recovery, nothing more.
That disclaimer out of the way I'm going to suggest a plant that most people already know about but might not know the real medical benefits of, garlic. Also known as Allium Sativum, garlic has been hailed as a curative for millenia, however in this modern world most people tend to discount "folk" remedies and in this case that is a mistake, doctors have been aware of measurable health benefits of the organic sulfur compounds in garlic for well over a century.
A potent natural antibiotic, garlic was used in world war one fairly commonly, and even in world war two when sulfate curatives ran out on the front lines. Certain forms of fungal infection respond better to garlic extracts than they do to the drug nyastatin and it was even used with some effect in trials for treatment of tuberculosis. Among these impressive uses garlic has been shown to lower blood pressure, act as a mild diuretic and clear serum cholesterol. All that being said, introducing garlic in to a bigger role in your diet is a great way to boost your health, however never use it instead of a doctor prescribed treatment! Seriously! Still, tastier than most pills with some butter and pasta.