Japanese knotweed - Itadori

A perennial plant of the Polygonaceae family (APG classification: Polygonaceae). The underground stems run horizontally and send up new shoots here and there. The stems are erect, reach a height of 1.5 meters, hollow, with purple-red spots, and branched at the top with small projections. The leaves are alternate, ovate, 6-15 cm long, with short, sharp tips and truncate bases. They are almost hairless except for coarse hairs on the veins. The petioles are 1-3 cm long and the sheaths are dry membranes. Flowers appear from July to October, in cone-shaped formations at the ends of branches emerging from the leaf axils. Dioecious. The perianth is white, 1.5 mm long. Male flowers have eight stamens. The three outer perianths of female flowers become large after flowering, with wings emerging from the back and enveloping the fruit, obovate, concave at the tip, and 8-10 mm long. The fruits are triangular, 2.5 mm long, and shiny black or dark brown. They are commonly found in wastelands from Hokkaido to Kyushu, and are also distributed in Korea and China. The stems have long been eaten as a wild vegetable, the young leaves are dried and used as a tobacco substitute, and the rhizomes are used medicinally. The species with red flowers is called Meigetsusou (bright moon grass) to distinguish it. On the Sea of ​​Japan side of Honshu, there are species with hairs gathering on the veins on the underside of the leaves, known as a variant of Katadori.

[Junko Kobayashi December 11, 2020]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

タデ科（APG分類：タデ科）の多年草。地下茎は横走して所々に新苗を出す。茎は直立し、高さ1.5メートルに達し、中空で紫紅斑(はん)があり、上部はよく分枝し、微小突起がある。葉は互生し、卵形で長さ6～15センチメートル、先は短く鋭くとがり、基部は切形(せっけい)。脈上に粗毛があるほかはほぼ無毛。葉柄は1～3センチメートル、鞘(さや)は乾膜質。花は7～10月、葉腋(ようえき)から出る枝の先に円錐(えんすい)状につく。雌雄異株。花被(かひ)は白色、長さ1.5ミリメートル。雄花には8本の雄しべがある。雌花は外側の花被3枚が花期後に大形となり背部に翼が出て果実を包み、倒卵形で先端はへこみ、長さ8～10ミリメートル。果実は三稜(さんりょう)形で長さ2.5ミリメートル、黒または黒褐色で光沢がある。北海道から九州にかけての荒れ地に普通にみられ、朝鮮、中国にも分布する。古くから山菜として茎を食用とするほか、若葉は乾燥してたばこの代用とし、根茎は薬用にする。花が紅色のものをメイゲツソウ（明月草）とよんで区別する。本州の日本海側には葉の裏面の脈上に毛の集まるものがあり、変種ケイタドリという。

［小林純子　2020年12月11日］

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