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 huáishān (), shānyào (山药, 山藥) (lit. "mountain medicine."), or huáishānyào (山药, 山藥). Rarely, also referred to as shǔyù (薯蕷).

In Japanese, it is known as nagaimo (lit. 'long yam'; kanji: 長芋). Furthermore, nagaimo is classified into ichōimo (lit. 'ginkgo-leaf yam'; kanji: 銀杏芋), or yamatoimo (lit. Yamato yam; kanji: 大和芋), depending on root shapes.

In Korea it is called ma (hangul: ), "sanwu (山芋, 산우)", seoyeo (薯蕷, 서여), or sanyak (山藥, 산약) and in Sri Lanka in Sinhala it is called wal ala (වැල් අල).

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] Nagaimo has also been used in traditional Chinese medicine.[4]

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.[5]

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. ^ Xu, Dermatology in Traditional Chinese Medicine, 2004
  5. ^ Takeguma, Massahiro. "Growing Nagaimo". Retrieved 26 July 2013. 

External links[edit]