Cycas revoluta - Cycas revoluta

An evergreen fern of the Dryopteris family. It has a short, ascending rhizome and produces bunches of monopinnate compound leaves 40-80 cm long. The scales on the petioles are sharply pointed and wider at the base. There are 10-25 pairs of pinnae, each narrow and sickle-shaped with an upward-curving tip. The veins are reticulate, and there are numerous scattered sporangia, which are circular and have an entire envelope. It grows under forests and along roadsides in Honshu and south. The variety, Cycadella japonica, is common in mountainous areas, has around 10 pairs of wide pinnae, and the envelope is saw-toothed.

C. caryotideum is common in the mountains south of Honshu, especially on limestone. The pinnae, which have sawtooth edges, are wider than those of C. japonica and number less than 10 pairs. A triangular ear is prominent at the front of the base. C. falcatum, which is found mainly near the coast from southern Hokkaido southwards, has large, dark green, glossy leaves and looks good, so it is also cultivated for ornamental purposes in Europe and the US. The pinnae are leathery and hard. Many C. japonica species are triploid, and are known to reproduce apogamously (a phenomenon in which cells other than egg cells divide independently to produce sporophytes).

[Harufumi Nishida]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

オシダ科の常緑性シダ。根茎は短く斜上し、長さ40～80センチメートルの1回羽状複葉を束生する。葉柄につく鱗片(りんぺん)は鋭くとがり、基部のものほど幅が広い。羽片は10～25対ほどで、先端が上向きに曲がる幅の狭い鎌(かま)形である。葉脈は網状、胞子嚢(のう)群は数多く散らばってつき、円形で全縁の包膜をもつ。本州以南の林下や路傍に生ずる。変種のヤマヤブソテツは山地に多く、幅の広い羽片が10対前後つき、包膜には鋸歯(きょし)がある。

　メヤブソテツC. caryotideumは、本州以南の山地の、とくに石灰岩地に多い。辺縁に鋸歯をもつ羽片は、ヤマヤブソテツよりさらに幅広く、数は10対以下と少ない。基部前側には三角形の耳状突起が目だつ。北海道南部以南の主として海岸近くに分布するオニヤブソテツC. falcatumは、大形で葉が暗緑色で光沢があり、見栄えがよいので欧米でも観賞用に栽植される。羽片は革質で堅い。ヤブソテツの仲間は三倍体が多く、無配生殖（卵細胞以外の細胞が単独に分裂し、胞子体を生ずる現象）を行うことが知られている。

［西田治文］

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