Mimosa pudica - sensitive plant

Japanese: オジギソウ - おじぎそう（英語表記）sensitive plant

It is a small shrub of the legume family (APG classification: Fabaceae), but in Japan it is usually treated as a spring-sown annual because it does not survive the winter. It is native to Brazil. It is known as Nemurigusa (sleeping grass), and its finely bushed, pinnately compound leaves close at night as a sleep, and are famous for closing when touched with a hand. This is due to a change in the turgor pressure of the cells in the pulvinus at the base of the petiole. It is also used as a teaching material in elementary and junior high schools. Its Chinese name, Ganshuusou, means shy grass, and its English name, Sensitive Grass, and its genus name, Mimosa, means "to imitate" in Greek, all of which are derived from this sleep behavior. It grows to a height of 20 to 30 centimeters, branches well, and grows thick along the ground. It produces clusters of globular pink flowers that bloom one after another from July to September, making it a very pretty plant. The seeds are sown in April and May and can be enjoyed in the garden or in a pot, but they grow best in sunny locations, are hardy and can even spread from scattered seeds.

[Somin Yanagi October 18, 2019]

Cultural history

The Portuguese monk José de Anchetta was the first to mention the property of the mimosa pudica's leaves opening and closing, observing it in Brazil in the mid-16th century. The Dutch scholar Yamamoto Boyo and the herbalist Ohara Toudou from Kishu (Wakayama Prefecture) wrote that it was introduced to Japan by the Dutch in 1841 (Tenpo 12). Toudou wrote in "Hyakka-Ko" (vol. 2, part 1, published in 1847) that "Today, among the common people, it is called Nemurigusa or Mimosa pudica and is played with."

[Hiroshi Yuasa October 18, 2019]

Mimosa pudica
From July to September, the inflorescences emerge from the leaf axils, and the spherical pink clusters of flowers open one after another. The leaves close at night, and when touched, they also close. Also known as Nemurigusa (sleeping grass). ©Shogakukan Photo by Masatoshi Hirose ">

Mimosa pudica

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

マメ科（APG分類：マメ科）の小低木であるが、日本では冬を越せないことが多いので、通常は春播(ま)き一年草として扱う。原産地はブラジル。ネムリグサ（眠草）といわれ、細かく茂る羽状複葉の葉は、夜になると葉を閉じる就眠運動をするほか、手などで触れると、その刺激で閉葉運動をするので有名である。これは葉柄基部の葉枕(ようちん)内の細胞の膨圧が変化するためである。小・中学校の教材としても使う。漢名の含羞草(がんしゅうそう)は恥ずかしがる草、英名は敏感な草で、属名のミモーサはギリシア語で「まねをする」という意味であり、いずれもこの就眠運動に由来する。草丈は20～30センチメートルでよく分枝し、枝は地をはうようにして茂り、7～9月に球状桃色の集合花を次々と開き、可憐(かれん)である。4～5月に種を播き、庭植え、鉢植えとして楽しむが、日当りのよい所でよく育ち、性質は強く、こぼれ種でも殖える。

［柳　宗民　2019年10月18日］

文化史

オジギソウの葉が開閉する性質に最初に触れたのは、ポルトガルの僧ジョゼー・デ・アンシェッタで、16世紀のなかばにブラジルで観察された。日本には1841年（天保12）にオランダ人が伝えたと、蘭学者(らんがくしゃ)の山本亡羊(ぼうよう)、紀州（和歌山県）の本草(ほんぞう)学者小原桃洞(おはらとうどう)が記す。桃洞は「今俗間にネムリグサ、あるいはオジギソウなどと名付け弄(もてあそ)ぶ」と『百品考』（2編上・1847刊）に書き残した。

［湯浅浩史　2019年10月18日］

オジギソウ

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