Robinia pseudoacacia (English spelling) locust-tree

Japanese: ニセアカシア - にせあかしあ（英語表記）locust-tree

A deciduous tall tree of the legume family (APG classification: Fabaceae). Its branches and leaves are similar to those of the Chinese sophora japonica, but it has thorns, so its Japanese name is Harienju (needle locust tree). It grows to a height of 15-20 meters. The bark is gray-brown with vertical cracks, and the branches have thorns that are modified from stipules, which grow opposite each other. The leaves are odd-pinnate and compound. There are 9-19 leaflets, oblong, 2-3.5 cm long, thin, and without sawtooth edges. In May and June, the axils produce 10-15 cm long racemes that hang down, and many butterfly-shaped, 1.5-2 cm long white flowers bloom. They are fragrant, contain a lot of high-quality nectar, and are a good source of nectar. The fruits are broad linear, 7-8 cm long, flat sheaths, and hairless. It contains 4-7 kidney-shaped, flat, black-brown seeds measuring 5-6 mm in length. Native to North America. Imported around 1874 (Meiji 7) for use as roadside and garden trees. Used as erosion control planting trees and fertilizer trees, its hard and heavy wood is used for civil engineering materials and firewood, and its leaves are used as fodder. This species is mistakenly called acacia in Hokkaido and other areas. Varieties include the thornless Robinia pseudoacacia Tinta, the shrub-like Robinia pseudoacacia Eikoctogena, and varieties with yellow-green leaves. A sun-loving tree that can withstand drought and cold, it can grow in any soil, and is fast-growing. It has strong sprouting power, and new seedlings will appear from the roots. It is propagated by seed, root division, and cuttings, and cuttings are easy to propagate by root cuttings.

[Yoshio Kobayashi November 20, 2019]

Cultural history

The original Acacia (genus) has small petals of the same shape, but instead has numerous stamens that spread out in a spherical shape, which makes it distinguishable from the butterfly-shaped species. American Indians ate the seeds. However, the plant contains harmful substances such as chrysarobin, piperonal, and sanguinarine. The origins of the false acacias in Sapporo are said to date back to 1881 (Meiji 14), when seedlings were moved from the Aoyama Colonization Office Experimental Station in Tokyo, and planted on Teishaba-dori in 1885. It is said that Kitahara Hakushu's "Road" was written in 1925 (Taisho 14) when he visited Sapporo and was reminded of the false acacias in his hometown of Yanagawa.

[Hiroshi Yuasa November 20, 2019]

[Reference] | Acacia

Robinia pseudoacacia
Since it grows quickly and can be grown in any location, it is often planted as a roadside tree or in a garden. It is also called harienju (Japanese spiny locust tree). © Yuya Fujino ">

Robinia pseudoacacia

Robinia pseudoacacia flower
From May to June, the racemes hang down from the leaf axils and produce numerous fragrant white, butterfly-shaped flowers. ©Seishohmaru ">

Robinia pseudoacacia flower

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

マメ科（APG分類：マメ科）の落葉高木。枝葉がエンジュに以ているが刺(とげ)があるので和名はハリエンジュ（針槐樹）という。高さ15～20メートル。樹皮は灰褐色で縦に割れ目ができ、枝に托葉(たくよう)の変化した刺が対生する。葉は互生し、奇数羽状複葉。小葉は9～19枚、長楕円(ちょうだえん)形で長さ2～3.5センチメートル、質は薄く、縁(へり)に鋸歯(きょし)はない。5～6月、葉腋(ようえき)に長さ10～15センチメートルの総状花序を垂れ下げ、蝶(ちょう)形で長さ1.5～2センチメートルの白色花を多数開く。芳香があり、良質の蜜(みつ)が多く、よい蜜源になる。果実は広線形で長さ7～8センチメートル、平たい鞘(さや)になり、毛はない。中に腎(じん)形で扁平(へんぺい)な長さ5～6ミリメートルの黒褐色の種子を4～7個含む。北アメリカ原産。1874年（明治7）ごろ街路樹、庭園樹用として輸入された。砂防用植栽木、肥料木に使われ、材は堅くて重く、土木用材、薪炭材に、葉は飼料とする。北海道などでアカシアと誤称されているのは本種である。品種に刺のないチンタオトゲナシニセアカシア、低木状のエイコクトゲナシニセアカシアがあり、葉が黄緑色の品種もある。陽樹で乾燥に耐え、耐寒性が強く、土地を選ばず、成長は速い。萌芽(ほうが)力も強く、根から新しい苗が出る。繁殖は実生(みしょう)、根分け、挿木などにより、挿木は根挿しが容易である。

［小林義雄　2019年11月20日］

文化史

本来のアカシア（属）は花弁が同形で小さく、かわりに多数の雄しべが球状に展開して目だつ点で、蝶形花(ちょうけいか)の本種とは区別できる。アメリカ・インディアンは種子を食用にした。ただし、植物体にはクリサロビン、ピペロナール、サンギナリンなどの有害物質を含む。札幌のニセアカシアは、1881年（明治14）東京・青山開拓使試験場から苗が移され、1885年停車場通りに植えたのが始まりとされる。北原白秋の『道』は1925年（大正14）白秋が札幌を訪れ、郷里柳川(やながわ)のニセアカシアを思い出してつくったと伝わる。

［湯浅浩史　2019年11月20日］

[参照項目] | アカシア

ニセアカシア

ニセアカシアの花

出典　小学館　日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について　情報 | 凡例

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