Chinese yam (Dioscorea opposita) is a root that is used in traditional Chinese medicine. The Chinese pharmaceutical name for this herbal is Rhizoma dioscoreae. Other names for Chinese yam include dioscorea and shan yao. Chinese yam is native to China, Japan, Korea, and Taiwan, where it can be found growing wild on hill slopes and in valleys. It is also propagated for medicinal and dietary uses.
The genus name Dioscorea is dedicated to the Greek physician and naturalist, Diosorides. There are between 600 and 800 different species of Dioscorea, making it one of the largest genera of the plant kingdom. Many species in this genus are grown and collected for their medicinal properties. Sweet potatoes are often called yams, although they are different plants.
The Chinese yam plant is a climbing vine that supports itself by coiling around the branches of other vegetation. The plant can be 9.75 ft (3 m) high and 5 ft (1.5 m) wide. Chinese yam has heart-shaped leaves and it produces small white flowers which have a cinnamon-like aroma. Small tubers (called tubercles) form in the axials (the angles between the leaves and the stem). These pea-sized tubercles are harvested in the late summer or early fall and are used to propagate the plant.
Chinese yam plants take three or four years to reach maturity, although fairly large roots may be harvested from well developed plants after the first year. Chinese yam is a spindle-shaped, thick, hard root or tuber that is white on the inside. However, cultivated forms from China or Japan may have different root shapes. The yam may be up to 1 yd (about 1 m) in length. Chinese yam is dug up in the winter. After the rough bark is removed, the root is washed and allowed to dry in either the shade or the sun. The dried root is rehydrated in water and then cut into slices.
Chinese yam contains large amounts of mucilage. Mucilage is a thick, slimy substance produced by plants. It has a soothing effect on mucous membranes, such as the tissues that line the respiratory passages. This may explain why Chinese yam is effective at relieving cough.
Traditional Chinese medicine classifies Chinese yam as neutral and sweet. It serves to tonify and augment the spleen and stomach; augment the lung yin and tonify the lung qi; and stabilize, tonify, and bind the kidneys. Chinese yam enters through the spleen, lung, and kidney channels (meridians). It is used as a tonic (restores tone to tissues). Chinese yam is used to treat weak digestion with fatigue and diarrhea, general weakness, frequent urination, decreased appetite, leukorrhagia (excessive vaginal discharge), premature ejaculation, the symptoms associated with diabetes, and chronic wheezing (whistling sound caused by breathing difficulty) and coughing.
Chinese yam should not be taken if the patient's symptoms include abdominal swelling and pain.
Chinese yam may be found in the dried or fresh form or as a powder. It is available in Asian food stores, Chinese pharmacies, and may be found in certain health food stores.
Chinese yam is taken by mouth for all indications. A tea (infusion) may be prepared by steeping slices of the root in boiling-hot water. The dosage is 10–30 g of root or 6–10 g of powder.
It is common in traditional Chinese medicine to mix herbs to treat specific sets of symptoms. Chinese yam may be combined with the following to treat certain symptoms as shown:
- poria and white atractylodes for loose, watery stools.
- codonopsis root for general weakness, fatigue, and poor appetite.
- Chinese foxglove root and cornus for lightheadedness, forgetfulness, insomnia, and related symptoms.
- ginseng (ren shen), white atractylodes rhizome (bai zhu), and poria (fuling) for weakness of the spleen and stomach characterized by poor appetite, lassitude (exhaustion, weakness), and diarrhea.
- white atractylodes rhizome, poria, and euryale seed (qian shi) for excessive dampness because of deficiency of the spleen characterized by white leukorrhagia and lassitude.
- phellodendron bark (huang bai) and plantain seed (che qian zi) for excessive dampness changing into heat characterized by yellow vaginal discharge.
- dogwood fruit (shan zhu yu) and dodder seed (tu si zi) for deficient kidneys characterized by lower back pain and leukorrhagia.
- astragalus root (huang qi), trichosanthes root (tian hua fen), pueraria root (ge gen), and fresh rehmannia root (sheng di huang) for the thirst, excessive drinking and eating, lassitude, and frequent urination associated with diabetes.
- dogwood fruit and prepared rehmannia root (shu di huang) for frequent nighttime urination because of deficient kidneys.
- bitter cardamon (yi zhi ren) and mantis egg case (sang piao xiao) for frequent urination because of deficient kidneys.
- glehnia root (sha shen), schisandra fruit (wu wei zi), and ophiopogon root (mai dong) for deficient lungs characterized by chronic cough
Species of Dioscorea that are edible have opposite leaves (leaves on the stem are directly across from one another), whereas species that are poisonous have alternate leaves (leaves on the stem are not directly across from one another).
Women who are pregnant or lactating should consult with a physician before using Chinese yam.
There are no side effects associated with the use of Chinese yam.
Chinese yam should not be taken with kan-sui root. As of mid-2000, there were no indications of any inter-actions between Chinese yam and any drug or other herbal medicine.
Copyright 2008 The Gale Group, Inc. All rights reserved.