Hondawara - Hondawara

Japanese: ホンダワラ - ほんだわら
Hondawara - Hondawara

This refers to brown algae, seaweed of the Sargassaceae family. This group is generally known as Mo or Moku, and some can grow to over 8 meters in length. Each has its own characteristic air vesicle, and there are about 70 species that grow in the seas near Japan, with about 30 of these species found mainly in Honshu. Like Japan, Australia in the southern hemisphere is also an area with many of these species. There are both annual and perennial algae, but there is no correlation between their size. Two well-known old names for Sargassum are Jinmesou (Shinbamo) and Nanolitho (Mokokumo).

Classification is based on macroscopic morphological characteristics, including the external appearance of roots, stems, leaves, pneumatology, crown leaves (leaflets or projections at the tip of the pneumatology), reproductive receptacles, etc. Even plant enthusiasts consider this type of classification difficult, because they do not have as many opportunities to come into contact with plants as they do with terrestrial plants, and it can be difficult to identify them if the above-mentioned organs are missing.

The genital receptacle is a reproductive organ that characterizes this species, and can be cylindrical, flat like a rice scoop, or branched. All of them contain numerous genital nests, inside which the antheridium and oophores are formed. Fertilization occurs between the sperm and eggs released from these, and the embryo develops into the main body. The genital receptacle is generally thin and long in males, and thick and short in females. However, there are some females, such as S. horneri, that are as long as 2 to 3 centimeters. The difference between males and females is clear in species such as S. horneri, but it is not easy to tell the difference in species with short genital receptacles of less than 5 millimeters.

Among the Sargassum genus, S. fulvellum is considered to be the representative species, but it is not very abundant. S. thunbergii grows at high water levels (near the low water line during neap tides) and is widely distributed, so it is the most common. Other common species include S. macrocarpum, S. ringgoldianum, and S. siliquastrum (Myagropsis myagroides, a different genus, is also common). S. patens is also very common, and serves as a substrate for the growth of mozuku (brown algae) and ogonori (red algae). S. muticum is distributed south of Miyagi Prefecture, but is now widely distributed on the Pacific coast of North America and in Europe. This is thought to be because when young oysters were exported from Japan, they were transported with young embryos of this species attached to them.

[Takeo Okuda]

use

In terms of current seaweed usage, the proportion of sargassum is not that large. However, it is clear that it has been deeply connected to life since ancient times, and sargassum is used in the Shiogama Shrine (Miyagi Prefecture) ritual of seaweed grilling, which is still carried on today. This ritual originates from the practice of piling up sargassum and pouring seawater over it to concentrate it in order to obtain salt, which was as important as rice as a basic ingredient in the diet. The name of nanolitho also appears in the Engishiki as a seaweed designated for taxation. Apart from being used as food, there is still a custom of decorating sargassum with Urajiro and Yuzuriha on Kagamimochi (rice cakes) during the New Year, or hanging them on gates. Furthermore, before the use of chemical fertilizers, sargassum was rotten and used as potassium fertilizer. Even today, potassium fertilizer is harvested in some coastal areas using this method.

[Takeo Okuda]

Sargassum and seaweed beds

A seaweed bed is a colony of large seaweed, also known as an underwater forest. There are three types of moba, depending on the species: kelp, sargassum, and eelgrass (flowering plants), and sargassum beds are also called "sargassum beds." Seaweed beds provide a place for small animals and fish in the sea to grow and spawn, forming an open yet highly productive biological community. It has been estimated that fishing production in seaweed beds is 5 to 17 times that in areas without seaweed beds, and as seaweed beds are now increasingly recognized as an indirect form of use, attempts are being made to create them artificially.

[Takeo Okuda]

[Reference] | Seaweed
Sargassum
©Shogakukan ">

Sargassum

Major types of brown algae (1) [specimen illustrations]
※Instructor: Makoto Yoshizaki © Fukuko Aoki ">

Major types of brown algae (1) [specimen illustrations]

Major types of brown algae (2) [specimen drawings and photographs]
※Instructors: Makoto Yoshizaki ©Fukuko Aoki ©Kanezo Otawa ©Shogakukan ">

Major types of brown algae (2) [specimen illustrations and labels]


Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

褐藻植物、ホンダワラ科の海藻をいう。一般にモ、モクとよばれる一群で、長いものでは8メートル以上になるものもある。それぞれ特徴のある気胞をもち、日本近海には約70種生育するが、うち約30種は本州を中心に分布する。南半球のオーストラリアも、日本と同様この類の多い地域である。一年生藻、多年生藻のいずれもあるが、大きさとの関連はない。なお、ホンダワラの古名としてよく知られているのがジンメソウ(神馬藻)、ナノリソ(莫告藻)である。

 分類は肉眼的な形態の特徴で行われ、根、茎、葉、気胞、冠葉(気胞の先端にある小葉あるいは突起)、生殖器床などの外形が取り上げられる。植物愛好家でもこの類の分類は困難なものと考えられているが、その原因は、陸上の草木のようには接する機会が多くないこと、前記の諸器官が欠けていると同定しにくい場合があることなどによる。

 生殖器床はこの類を特色づける生殖器官で、円柱状のもの、しゃもじ状に平たいもの、分岐するものなどがある。いずれも多数の生殖器巣を内蔵し、その内部に造精器、生卵器を形成する。それらから放出された精虫と卵で受精が行われ、発生体は本体となっていく。生殖器床は一般に雄は細くて長く、雌は太くて短い。しかしアカモクS. horneriのように雌でも2~3センチメートルと長いものもある。アカモクなどでは雌雄の差は明らかであるが、生殖器床が5ミリメートル以下の短い種類ではその区別は容易ではない。

 ホンダワラ属のなかでは、種としてのホンダワラS. fulvellumは代表種のように思われるが、量的にはさほど多くない。ウミトラノオS. thunbergiiはこの類のなかでは高い水位(小潮時の低潮線近く)に生育し、分布も広いため、もっともみかける機会が多い。ほかにノコギリモクS. macrocarpum、オオバモクS. ringgoldianum、ヨレモクS. siliquastrumなどが一般的である(別属のジョロモクMyagropsis myagroidesも同様に多い)。またヤツマタモクS. patensもごく普通にみられ、モズク(褐藻植物)やオゴノリ(紅藻植物)の着生基盤となっている。タマハハキモクS. muticumは宮城県以南に分布するが、現在は北米太平洋岸やヨーロッパでも大繁殖している。これは、日本からカキの稚貝が輸出された際、本種の幼胚(ようはい)が付着して運ばれたためと考えられている。

[奥田武男]

利用

現在の海藻利用の面からみると、ホンダワラ類の比重はさほど大きくない。しかし、古くから生活とのかかわりが深かったことは明らかで、いまも継承されている塩竈(しおがま)神社(宮城県)の藻塩焼(もしおやき)の神事ではホンダワラが使われている。これは、食生活上の基礎として米とともに重要であった塩を得るために、ホンダワラ類を積み重ね、海水をかけて濃縮したことに由来する神事である。また、『延喜式(えんぎしき)』のなかには、租税として指定された海藻としてナノリソの名がみえる。食用以外では、正月の鏡餅(かがみもち)にウラジロ、ユズリハなどとともにホンダワラをいっしょに飾ったり、門に掲げる風習が残されている。さらに、化学肥料が使用される以前は、ホンダワラ類は腐らせてカリ肥料とされてきた。現在でも、一部の海岸地帯では、この方法によってカリ肥料を収穫している。

[奥田武男]

ホンダワラ類と藻場

藻場(もば)とは大形海藻の群落のことで、海中林ともよばれる。構成種によりコンブ類、ホンダワラ類、アマモ類(顕花植物)の三つがあり、ホンダワラ類の場合は「ガラモ場」ともよばれる。藻場は海中の小動物や魚類にとって、成育あるいは産卵の場となるので、開放的ながらも生産性の高い生物社会が形成されることとなる。藻場での漁業生産は、藻場のない所の5~17倍とも試算されており、現在では間接的な利用形態としての藻場の認識が深まるとともに、人工的な造成が試みられるに至っている。

[奥田武男]

[参照項目] | 海藻
ホンダワラ
©Shogakukan">

ホンダワラ

褐藻植物のおもな種類(1)〔標本画〕
※指導:吉崎 誠©青木福子">

褐藻植物のおもな種類(1)〔標本画〕

褐藻植物のおもな種類(2)〔標本画・標本写真〕
※指導:吉崎 誠©青木福子 ©大多和鐘三 ©Shogakukan">

褐藻植物のおもな種類(2)〔標本画・標…


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