Dioscorea opposita

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Grated Dioscorea opposita (Japanese tororo)
Tororo blackbean udon from Tamba (丹波の黒豆とろろうどん)

Dioscorea opposita (nagaimo, Chinese yam, Korean yam) is a name commonly used for two plants correctly known as Dioscorea polystachya and Dioscorea oppositifolia. This page is about D. polystachya, a type of yam (Dioscorea) that can be eaten raw.

It is an exception to the rule that yams must be cooked before consumption (due to harmful substances in the raw state). In Japanese cuisine, it is eaten raw and grated, after only a relatively minimal preparation: the whole tubers are briefly soaked in a vinegar-water solution, to neutralize irritant oxalate crystals found in their skin. The raw vegetable is starchy and bland, mucilaginous when grated, and may be eaten plain as a side dish, or added to noodles.

It is used in the Japanese noodle dish tororo udon/soba and as a binding agent in the batter of okonomiyaki. The grated nagaimo is known as tororo (in Japanese). In tororo udon/soba, the tororo is mixed with other ingredients that typically include tsuyu broth (dashi), wasabi, and green onions.


The plant correctly called D. opposita is now considered to be the same species as D. oppositifolia.[1] The plant correctly called Dioscorea polystachya is often misidentified as Dioscorea opposita. Botanical works that point out that error may list, e.g., Dioscorea opposita auct. non Thunb. as a synonym of D. polystachya.[2]


In Chinese it is known as huái shān (), shān yào (山药) (lit. "mountain medicine."), or huái shān yào (山药).

In Japanese, it is known as nagaimo (lit. 'long yam'; kanji: 長芋; hiragana: ながいも). Furthermore, nagaimo is classified into ichōimo (lit. 'ginkgo-leaf yam'; kanji: 銀杏芋; hiragana: いちょういも), or yamatoimo (lit. Yamato yam; kanji: 大和芋; hiragana: やまといも), depending on root shapes.

In Korea it is called ma (hangul: 마), "sanwu(山芋, 산우)", seoyeo(薯蕷, 서여), or sanyak(山藥, 산약).

In Vietnam, the yam is called củ mài or khoai mài. When this yam is processed to become a medicine, the yam is called hoài sơn or tỳ giải.

In the Ilokano language of the northern Philippines it is called tuge.

In alternative medicine[edit]

Creams and dietary supplements made from Dioscorea villosa are claimed to contain human hormones and promoted as a medicine for a variety of purposes, including cancer prevention and the treatment of Crohn's disease and whooping cough. However, according to the American Cancer Society, the claims are false and there is no evidence to support these substances being either safe or effective.[3]

Traditional chinese medicine[edit]

The tuber is also used (often in dried form) in traditional Chinese medicine and Chinese herbology.

Shanyao root, 山藥, Radix Dioscoreae oppositae, falls within the Chinese herbal medicine category of Tonify Qi materia medica.[4][5] Within this category it has specialized and important properties which make it one of the most important and commonly used materia medica in the Chinese medicine repertoire. As a tonifying herb which enters the kidney organ (Zang) and/or channel (Jing), its role is fundamental, in accordance with the dictum that "the kidney is the root of Yin and Yang of all the organs (Zang-fu). Shanyao is classified as being of neutral temperature, an important property which means that, while it significantly tonifies the Qi, it does not at the same time cause Heat; in this way it is able to tonify Qi without injuring the Yin, an important advantage in the treatment of patients with deficient Yin. In this role of tonifying Qi without injuring the Yin it appears in such classical formulas as Liu Wei Di Huang Wan, 六味地黃丸, the Six Flavours Rehmannia Pill, and its many derivative and related formulas.[6]

Shan Yao is also used in situations where it is necessary to tonify Qi, but where the Yin is not deficient. In this usage it is usually used prepared by dry-frying (chao, 炒), which alters its temperature property to slightly Warm. The slightly Warm property enables it to Warm the spleen, another organ/channel which it enters, enabling the spleen to Dry Dampness, but without injuring Blood, a dimension of the Yin. A typical formula where dry-fried Shan Yao is used to tonify Spleen Qi is Shen Ling Bai Zhu San, 參苓白術散, Ginseng Poria Atractylodes Powder.[7] It is also frequently found dry-fried in Chinese herbal dermatology[8] in formulas for treating Blood Dryness where it is necessary to warmly tonify Spleen Qi, to enable it to Transform residual Dampness, but without drying Blood or Yin.

Growing Nagaimo[edit]

Nagaimo growing cycle span approximately one year, and should be planted between winter and spring. The traditional methods growing it are: using smaller tubers, top cut of bigger tubers or through cuttings of branches. The first two methods can produce 20 cm (7.8 in) long tubers and above. The latter produces smaller tubers (10 cm or 4 in) that are usually replanted for the next year.

Between 7 and 9 months of replanting nagaimo seedlings, their leaves start to get dry (a common fact in plants that grow tubers): that indicates that it’s time to harvest. At home gardens, it is interesting to harvest only what will be consumed, leaving the rest at the pot in a moist soil.[9]

See also[edit]


  1. ^ "World Checklist of Selected Plant Families, entry for Dioscorea oppositifolia". Retrieved 12 August 2014. 
  2. ^ "USDA GRIN Taxonomy". Retrieved 12 August 2014. 
  3. ^ "Wild Yam". American Cancer Society. November 2008. Retrieved 21 September 2013. 
  4. ^ Bensky, Clavey, Stöger and Gamble, Chinese Herbal Medicine: Materia Medica, Seattle, 2004, p. 723 ff
  5. ^ Xu and Wang, Chinese Materia Medica: Combinations and Applications, 2002, p. 526 ff
  6. ^ Scheid, Bensky, Ellis & Barolet, Chinese Herbal Medicine: Formulas and Strategies, Seattle, 2009, p. 365 ff.
  7. ^ Scheid, Bensky, Ellis & Barolet, Chinese Herbal Medicine: Formulas and Strategies, Seattle, 2009, p. 314 ff.
  8. ^ Xu, Dermatology in Traditional Chinese Medicine, 2004
  9. ^ Takeguma, Massahiro. "Growing Nagaimo". Retrieved 26 July 2013. 

External links[edit]