Hego - Hego

A large evergreen tree fern of the Cyatheaceae family. It prefers humid forests. The stems reach 4 meters in height and 50 centimeters in diameter at the base, and rarely branch. Leaves over 2 meters in length open out from the top of the stem. The petioles are shorter than the blades, purple-brown and densely covered with thorns, and bear dark brown scales with thorns on the margins. The blades are twice pinnately divided, the pinnules are deeply pinnately lobed, and bear numerous sporangia covered with a thin membrane on the underside. It is commonly found in the southern Kii Peninsula and Hachijo Island, and is commonly seen in Shikoku, southern Kyushu, and south of Yakushima. It is also distributed in the Ogasawara Islands. In addition to this species, there are six other closely related species in Japan. The large C. lepifera of the Okinawa Islands reaches 7 meters in height, and unlike the Cyathe, it does not have a membrane and the scales do not have thorns. C. mertensiana, found in the Ogasawara Islands, is a closely related species, and both are indicator plants of the subtropics, so they are often cultivated in large greenhouses. C. hancockii, found in the Kii Peninsula as its northernmost limit, is a small species found in the northernmost part of the Cyatheaceae family, and its rhizomes do not grow upright but rather obliquely upward. Unlike the trunks of trees, the stems of Cyatheaceae do not grow large, but are thickly covered with countless adventitious roots that grow from the stems, making them thick at the base. This layer of adventitious roots retains an appropriate amount of humidity and air, making it suitable for cultivating epiphytic orchids and ferns, and is sold commercially as staghorn fern boards. In Southeast Asia and Central and South America, the stems and roots are carved into souvenirs. In addition, the stems contain a large amount of starch, so they were once eaten by the indigenous people of New Zealand and many other areas.

[Harufumi Nishida]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

ヘゴ科の常緑性大形の木生シダ。湿度の高い林中を好む。茎は高さ4メートル、基部の径は50センチメートルに達し、まれに枝分れする。茎の上部には、長さ2メートルを超す葉が開出する。葉柄は葉身より短く、紫褐色で刺(とげ)が密生し、暗褐色の辺縁に刺のある鱗片(りんぺん)をつける。葉身は2回羽状に分裂、小羽片は羽状に深裂し、裏面に薄い包膜で覆われた胞子嚢(のう)群を多数つける。紀伊半島南部や八丈島を北限とし、四国、九州南部、屋久(やく)島より南でよくみかけられる。また、小笠原(おがさわら)諸島にも分布する。日本には本種のほかに6種の近縁種がある。沖縄諸島のヒカゲヘゴC. lepiferaは大形で高さ7メートルに達し、ヘゴと異なり包膜がなく、鱗片に刺がない。小笠原諸島に産するマルハチC. mertensianaはこの近縁種で、いずれも亜熱帯の指標植物であることから、大型温室には好んで栽植される。紀伊半島が北限のクサマルハチC. hancockiiは、ヘゴ科のなかでもっとも北に分布する小形種で、根茎は直立せず斜上する。ヘゴ科の茎は樹木の幹と異なり肥大成長をしないが、茎から出る無数の不定根に厚く覆われ、基部が太くなる。この不定根の層は湿度と空気とを適度に保持するため、着生のランやシダ類の栽培に適し、ヘゴ板(いた)として市販される。東南アジアや中南米では、茎や根塊を彫刻して土産(みやげ)品とする。また、茎はデンプンを多量に含むため、ニュージーランドをはじめ多くの地域で、かつては原住民がこれを食用とした。

［西田治文］

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