Ragweed - Butakusa

An annual plant of the Asteraceae family. The stem is erect and 0.5 to 1.5 meters tall. The leaves grow opposite each other at the bottom of the stem and alternate at the top. The leaf blade is 2 to 3 times pinnate, the lobes are linear, and the texture is thin and soft. Monoecious. From July to October, the male flower heads grow in long spikes at the ends of the branches, and 2 to 3 female flower heads grow in the axils below them. During the flowering season, the wind blows a large amount of spherical pollen, which can cause hay fever, including allergic rhinitis, conjunctivitis, and bronchial asthma. A naturalized plant native to North America, it was introduced in the early Meiji period and is rampant in wastelands in various cities. The name is a translation of the English common name hogweed.

[Hiroyuki Koyama]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

キク科の一年草。茎は直立し、高さ0.5～1.5メートル。葉は茎の下部では対生し、上部では互生する。葉身は2、3回羽裂し、裂片は線形、質は薄くて柔らかい。雌雄同株。7～10月、雄性頭花は枝先に長い穂状につき、雌性頭花はその下部の葉腋(ようえき)に2、3個つく。花期に球形の花粉を多量に風によって飛ばすが、これはアレルギー性の鼻炎、結膜炎、気管支喘息(ぜんそく)など、花粉症の原因となる。北アメリカ原産の帰化植物で、明治初期に渡来し、各都市の荒れ地などにはびこっている。名は、英語の通称名hogweedの訳からついた。

［小山博滋］

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