Himemukashi mugwort - Himemukashi mugwort

An annual or biennial plant of the Asteraceae family. The stem is erect, 1-2 meters tall, and the whole plant is covered with coarse hairs. From August to October, it produces panicles with many small flower heads, each 3 mm in diameter. The ray flowers are small, but white and somewhat conspicuous. The name comes from the fact that in small individuals, the whole plant resembles mugwort, but the flower heads are smaller. A naturalized plant native to North America, it was introduced to Europe at the end of the 17th century and to Japan around the beginning of the Meiji era, and is now widely distributed around the world. It is also known as Meiji-sou (Meiji grass) and Goishingusa (Goishingusa), which comes from the time of its introduction. It is also known as Tetsudougusa (railroad grass), which comes from the fact that it grows and spreads along railroad tracks.

There are similar species such as the common ragweed and the large common ragweed, but these do not develop ray flowers at all. Both are naturalized plants, but they are from different lineages than the common mugwort. They are shorter in height and are closer to the common mugwort, which has prominent ray flowers.

[Hiroyuki Koyama]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

キク科の一年草または越年草。茎は直立し、高さ1～2メートル、全草に粗い毛が多い。8～10月、円錐(えんすい)花序をつくり、径3ミリメートルの小さな頭花を多数つける。舌状花は小さいが、白色でやや目だつ。名は、小さな個体では全草がムカシヨモギに似るが、頭花がより小さいことに由来する。北アメリカ原産の帰化植物で、ヨーロッパには17世紀末に入り、日本には明治初年ころ渡来し、現在では世界に広く分布している。別名メイジソウ（明治草）、ゴイッシングサ（御一新草）というが、これは渡来した時期に由来する。またテツドウグサ（鉄道草）の名もあるが、これは鉄道に沿って生え広がったことに由来する。

　よく似た種にアレチノギクやオオアレチノギクがあるが、これらでは舌状花はまったく発達しない。いずれも帰化植物であるが、ヒメムカシヨモギとは系統が異なる。草丈が低く、舌状花の顕著なムカシヨモギにより近い。

［小山博滋］

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