Evening primrose - Evening primrose

A biennial plant of the Onagraceae family (APG classification: Onagraceae). The root is a white taproot. The basal leaves are oblanceolate and rosette-shaped. The stem is 1.5 meters tall, covered with white hairs and has red granular protrusions. The leaves are alternate, stalked, narrowly oblong, hairy, and have white midribs. The flowering season is July to September. The buds are obtusely rectangular. There are four calyxes that join together to encase the flower, and before blooming, they are yellowish-red and curl back in pairs. The four petals are pale yellow, obovate, 4 to 5 cm long, and do not turn red after wilting (evening primrose and other plants do turn red). There are eight stamens, the style is longer than the stamens, and the stigma is four-lobed. The capsule is cylindrical, 3-4 cm long, covered with fine white hairs, and divides into four lobes when ripe.

It is a naturalized plant native to North America that was introduced to Japan in the early Meiji period and is found from Hokkaido to Kyushu, often found on riverbanks and roadsides. It blooms in the evening and wilts the next morning, so it has long been known as "yoimachigusa" (evening grass) along with its related species, evening primrose and moonflower. It is also well known that in 1900, Dutch botanist de Vries used it as a test material for mutations. In addition to being used as an ornamental plant, the young leaves are edible.

[Junko Kobayashi, August 20, 2020]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

アカバナ科（APG分類：アカバナ科）の二年草。根は白色の直根。根出葉は倒披針(とうひしん)形でロゼット状をなす。茎は高さ1.5メートル、白毛に覆われ、赤色の粒状突起がある。葉は互生し、有柄、狭長楕円(だえん)形で細毛があり、主脈は白い。花期は7～9月。つぼみは鈍四角形。萼(がく)は4枚で、合着して花を包み、開花前は帯黄赤色で2片ずつ反り返る。花弁は4枚、淡黄色、倒卵形で長さ4～5センチメートル、しぼんでから紅変しない（マツヨイグサなどは紅変する）。雄しべ8本、花柱は雄しべより長く、柱頭は4裂する。蒴果(さくか)は円柱形で3～4センチメートル、細白毛に覆われ、熟すと4裂する。

　明治初年に日本に入った北アメリカ原産の帰化植物で、北海道から九州に分布し、川原や道端に多い。夕方開花し翌朝しぼむので近縁種のマツヨイグサ、ツキミソウとともに「宵待草(よいまちぐさ)」とよばれて古くから親しまれている。また1900年、オランダの植物学者ド・フリースにより、突然変異の実験材料として用いられたことは有名である。観賞用のほか、若葉は食用となる。

［小林純子　2020年8月20日］

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