Wild yam, also known as Dioscorea villosa, China root, Mexican yam, colic root, devil's bones, rheumatism root, yuma, and rheumatism root,  is a climbing vine native to North America.  It's usually found growing in damp woods and swamps.  It was popular with the Aztec and Mayan people who used it to treat many ailments, especially to relieve pain during child birth and other female problems such as hot flashes, night sweats and mood swings caused by PMS.  It is also used for arthritis and asthma.  It is useful in treating irritable bowel syndrome, gastritis and gall bladder problems, upset stomach and coughs.  It can help pregnant women with cramps or nausea.  Some people recommend it as an herbal contraceptive.  It is useful in strengthening the liver and endocrine system.  It contains an alkaloid that can help lower blood sugar.  It helps to increase the HDL (good) cholesterol in the elderly.  Researchers have theorized that taking wild yam may help reduce levels of cholesterol in the blood, although studies have shown mixed results.  The Chinese use it to aid digestion and to relax muscles.  Ayurvedic practitioners recommend it for impotence and infertility.  It regulates metabolism.