Onidokoro - Onidokoro

A perennial climbing plant of the Dioscoreaceae family (APG classification: Dioscoreaceae). It is also called simply tokoro. The rhizome grows horizontally and is somewhat thickened but hard. Unlike Dioscorea yams, the roots do not swell. The leaves are alternate, the leaf blade is cordate and entire, 5-12 cm long and 5-10 cm wide. The flowering season is July-August. The flowers are unisexual and dioecious. The male inflorescence is erect, with short stalks and six stamens. The female inflorescence is drooping, the female flower is sessile, and the capsule is made of three wings and has three lobes. Each lobe contains two seeds. It is endemic to Japan, commonly growing in fields and forest edges, and is distributed from Hokkaido to Kyushu. The curved rhizome with many hairy roots is called yaro (old man) because it resembles an old man, and is decorated with oranges, kelp, and persimmons during the New Year to celebrate longevity. Yaro is said to be a contrast to shrimp. In the Tohoku region, young rhizomes are often soaked in water to remove the bitterness before eating.

Other wild species of Dioscorea in Japan include Chinese yam, bitter yam, Japanese yam, and fan-shaped yam.

[Takemi Shimizu October 19, 2018]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

ヤマノイモ科（APG分類：ヤマノイモ科）のつる性多年草。単にトコロともいう。根茎は横に伸び、やや肥厚するが硬い。根はヤマノイモと異なって肥大しない。葉は互生、葉身は心臓形で全縁、長さ5～12センチメートル、幅5～10センチメートル。花期は7～8月。花は単性で雌雄異株。雄花序は直立、雄花は短柄をつけ、6本の雄しべがある。雌花序は下垂し、雌花は無柄、蒴果(さくか)は3枚の翼からなり、3室。1室に2個の種子がある。日本特産で、原野や林縁に普通に生え、北海道から九州にかけて分布する。ひげ根が多く、曲がった根茎を老人にたとえて野老(やろう)とよび、正月には橙(だいだい)、昆布、串柿(くしがき)などとともに飾って長寿を祝った。野老は海老(えび)に対比させたものといわれる。東北地方では若い根茎をよくあく抜きして食べる。

　ヤマノイモ属の日本の野生種には、ほかにヤマノイモ、ニガカシュウ、タチドコロ、ウチワドコロなどがある。

［清水建美　2018年10月19日］

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