出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/10/20 23:34:25」(JST)
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| イネ科 | ||||||||||||||||||
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| Poaceae (R.Br.) Barnhart | ||||||||||||||||||
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イネ科（イネか、Poaceae）は、おおよそ700属と8000種が属する被子植物単子葉類の大きな科である。世界中で広く分布する[1]。古くは禾本科（かほんか）又はホモノ科とも呼んだ。
草本か、あるいは木質化した中空の茎をもつ木本的な植物である[1]。
葉は平行脈をもち、細長く、薄いものが多い。一部で基部でねじれて裏表逆転するものがある。葉は根元から生える根出葉と、茎の途中に生える茎葉がある。ススキのように根出葉が多いものもあれば、ヨシのように茎葉が多いものもある。一部のものは、匍匐枝や地下茎があって横に這う。
葉の基部が茎に巻き付いて葉鞘を形成するが、カヤツリグサ科のように、葉鞘の両端が融合して筒になることは少ない。また、葉鞘の先端にヒレのような出っ張りが生じ、これを葉舌（ようぜつ）という。葉身が葉鞘に至るところで膨らむことがあるがここを葉耳と呼ぶ。葉舌、葉耳を種の同定の目安にするグループも少なくない。
茎は節があり、節ごとに葉がつき、根が円周上に出る。茎は往々にして中空で、節の所がしきりになる。茎は木質化して堅くなる場合があり、特にタケ亜科のものは材木に使えるほど丈夫になる。ただし、形成層はないので、成長して太くなることはない。タケ亜科は分類体系によってはイネ科から分離し、タケ科として扱うこともある。
イネ科植物は、花粉媒介を風によっておこなう風媒花へと進化したものである[1]。そのため、その花は花弁などを失い、雌しべは長くて毛が生えていることが多い。また、花序が変形した小穂と呼ばれる偽花を単位とし、これが集合して穂を形成する。小穂内の子房が成熟した果実を穎果と呼び、これがさらに外穎と内穎、時には苞穎も加わった籾殻にくるまれる。風媒ではあるが、花粉を食物とするハエの仲間やハナバチなどの昆虫が訪れるのを見ることも多く、イネ科の花粉を専門に集めるハナバチもある。ただし、麦角菌に感染したイネ科植物の穂に昆虫が集まるのは、麦角菌が分生子を含んだ蜜を分泌するためである。
比較的下等なものでは小穂は多数の同じような花を並べた形であり、より進んだものでは、部分的な退化や様々な特殊化が見られる。雄花と雌花の分化が見られるものもある。なお、このような特徴はイネ科の属の分類には欠かせない重要な特徴である。そのため、不明のイネ科の同定をおこなう場合、花が咲く直前のものを調べるのがよいとされている。
非常に種類が多く、実に様々な環境に生育するものがある。森林や高山に生育するものもあるが、草原はイネ科の植物を中心に構成されることが多い。
双子葉植物が生育する草地では、一番上の層に同化組織が集中し、その内部は暗くなる傾向があるが、イネ科植物の形成する草原は、茎も葉も立っているので、根元まで光が入る。
水辺にもカヤツリグサ科やイグサ科とともに大きな群落をなす種がある。
イネ（米）、コムギ（小麦）、トウモロコシ、オオムギ、ライムギなど、狭義の穀物はイネ科に属する。その他サトウキビやタケなど馴染深い資源植物が多く含まれる。ススキやパンパスグラスもイネ科に属する。
代表的な使用例
また肉食動物のネコも燕麦などのイネ科の植物を時折食べる習性を持つため、飼い猫用に猫草としてペットショップなどで売られている事もある。
イネ科は、初期に枝分かれしたいくつかの原始的で互いには疎遠な亜科と、BEP clade（イネ、ムギ、タケなど）、PACAD clade（トウモロコシ、キビ、ヒエ、ススキなど）という2つの大きな単系統に分かれる。BEP clade と PACAD clade は互いに姉妹群である。[2]
亜科・連への分け方は諸説あるが、系統が明らかになるにつれまとまりつつある。ここに示すのはGrass Phylogeny Working Group[3] による12亜科約40連である。さらに Micrairoideae 亜科を認める説もある[4]が、最近の研究によれば Micrairoideae は単系統ではなく[2]位置づけは不確実である。
亜連は省略し、属・種は重要なもののみリストアップしている。
タケ類。かつてはイネ科のうち最初に分岐したという説もあり、タケ科 Bambusaceae とする場合もあった。
イネ亜科 Oryzoideae とも。
小穂は多数花、二花の場合、先端から退化傾向。
Micrairoideae亜科を認める場合は PACCMAD clade とすることもある。
小穂は二花、下側は実をつけない傾向。
メヒシバ
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エノコログサ
| ウィキメディア・コモンズには、イネ科に関連するカテゴリがあります。 |
| ウィキスピーシーズにイネ科に関する情報があります。 |
| Poaceae (true grasses) Temporal range: Late Cretaceous[1] - recent, 66–0 Ma PreЄ
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| Flowering head of meadow foxtail (Alopecurus pratensis), with stamens exerted at anthesis | |
| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Monocots |
| (unranked): | Commelinids |
| Order: | Poales |
| Family: | Poaceae Barnhart[2] |
| Type genus | |
| Poa L. |
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The Poaceae (English pronunciation: /poʊˈeɪ.siˌiː/) (also called Gramineae or true grasses) are a large and nearly ubiquitous family of monocotyledonous flowering plants. With more than 10,000 domesticated and wild species, the Poaceae are the fifth-largest plant family, following the Asteraceae, Orchidaceae, Fabaceae, and Rubiaceae.[3] Though commonly called "grasses", seagrasses, rushes, and sedges fall outside this family. The rushes and sedges are related to the Poaceae, being members of the order Poales, but the seagrasses are members of order Alismatales.
Grasslands are estimated to constitute 20% of the vegetation cover of the Earth. Poaceae live in many other habitats, including wetlands, forests, and tundra.
Domestication of poaceous cereal crops such as maize (corn), wheat, rice, barley, and millet lies at the foundation of sedentary living and civilization around the world, and the Poaceae still constitute the most economically important plant family in modern times, providing forage, building materials (bamboo, thatch) and fuel (ethanol), as well as food.
Grasses generally have the following characteristics (the image gallery can be used for reference):
Poaceae have hollow stems called culms plugged at intervals by solid leaf-bearing nodes. Grass leaves are nearly always alternate and distichous (in one plane), and have parallel veins. Each leaf is differentiated into a lower sheath hugging the stem and a blade with entire (i.e., smooth) margins. The leaf blades of many grasses are hardened with silica phytoliths, which discourage grazing animals; some, such as sword grass, are sharp enough to cut human skin. A membranous appendage or fringe of hairs called the ligule lies at the junction between sheath and blade, preventing water or insects from penetrating into the sheath.
Flowers of Poaceae are characteristically arranged in spikelets, each having one or more florets. The spikelets are further grouped into panicles or spikes. The part of the spikelet that bears the florets is called the rachilla. A spikelet consists of two (or sometimes fewer) bracts at the base, called glumes, followed by one or more florets. A floret consists of the flower surrounded by two bracts, one external—the lemma—and one internal—the palea. The flowers are usually hermaphroditic—maize being an important exception—and anemophilous or wind-pollinated. The perianth is reduced to two scales, called lodicules, that expand and contract to spread the lemma and palea; these are generally interpreted to be modified sepals. This complex structure can be seen in the image on the right, portraying a wheat (Triticum aestivum) spikelet.
The fruit of Poaceae is a caryopsis, in which the seed coat is fused to the fruit wall.
A tiller is a leafy shoot other than the first shoot produced from the seed.
Grass blades grow at the base of the blade and not from elongated stem tips. This low growth point evolved in response to grazing animals and allows grasses to be grazed or mown regularly without severe damage to the plant.[4]
Three general classifications of growth habit present in grasses: bunch-type (also called caespitose), stoloniferous, and rhizomatous.
The success of the grasses lies in part in their morphology and growth processes and in part in their physiological diversity. Most of the grasses divide into two physiological groups, using the C3 and C4 photosynthetic pathways for carbon fixation. The C4 grasses have a photosynthetic pathway, linked to specialized Kranz leaf anatomy, which allows for increased water use efficiency, rendering them better adapted to hot, arid environments and those lacking in carbon dioxide.
The C3 grasses are referred to as "cool-season" grasses, while the C4 plants are considered "warm-season" grasses; they may be either annual or perennial.
Grass-dominated biomes are called grasslands. If only large, contiguous areas of grasslands are counted, these biomes cover 31% of the planet's land.[5] Grasslands include pampas, steppes, and prairies.
Grasses provide food to many grazing mammals—such as livestock, deer, and elephants—as well as to many species of butterflies and moths.
The evolution of large grazing animals in the Cenozoic contributed to the spread of grasses. Without large grazers, fire-cleared areas are quickly colonized by grasses, and with enough rain, tree seedlings. Trees eventually shade out and kill most grasses. Trampling grazers kill seedling trees but not grasses.[6]
| Phylogeny of the grasses | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Cladogram showing subfamilies and in brackets approximate species numbers.[7] |
Until recently, fossil findings indicated that grasses evolved around 55 million years ago. Recent findings of grass-like phytoliths in Cretaceous dinosaur coprolites have pushed this date back to 66 million years ago.[1][8] Indeed, revised dating of the origins of the rice tribe Oryzeae suggest a date as early as 107 to 129 Mya.[9]
The relationships among the subfamilies Bambusoideae, Ehrhartoideae and Pooideae in the BEP clade have been resolved: Bambusoideae and Pooideae are more closely related to each other than to Ehrhartoideae.[10] This separation occurred within a relatively short time span (about 4 million years).
The grass family is one of the most widely distributed and abundant groups of plants on Earth. Grasses are found on every continent,[11] and are absent only from central Greenland and much of Antarctica.[12]
Recent classifications of the grass family[13] recognize 12 subfamilies and a small number of taxa with uncertain placements:
Depending on the classification followed, the family includes around 668 genera.[3]
The Poaceae name was given by John Hendley Barnhart in 1895,[14] based on the tribe Poeae (described in 1814 by Robert Brown), and the type genus Poa (described in 1753 by Linnaeus). The term is derived from the Ancient Greek term for grass.
Grasses are, in human terms, perhaps the most economically important plant family. Grasses' economic importance stems from several areas, including food production, industry, and lawns.
Agricultural grasses grown for their edible seeds are called cereals or grains (although the latter term, agriculturally, refers to both cereals and legumes). Three cereals – rice, wheat, and maize (corn) – provide more than half of all calories eaten by humans.[15] Of all crops, 70% are grasses.[16] Cereals constitute the major source of carbohydrates for humans and perhaps the major source of protein, and include rice in southern and eastern Asia, maize in Central and South America, and wheat and barley in Europe, northern Asia and the Americas.
Sugarcane is the major source of sugar production. Many other grasses are grown for forage and fodder for animal feed, particularly for sheep and cattle, thereby indirectly providing more human calories.
Grasses are used for construction. Scaffolding made from bamboo is able to withstand typhoon-force winds that would break steel scaffolding.[5] Larger bamboos and Arundo donax have stout culms that can be used in a manner similar to timber, and grass roots stabilize the sod of sod houses. Arundo is used to make reeds for woodwind instruments, and bamboo is used for innumerable implements.
Grass fiber can be used for making paper, and for biofuel production.
Phragmites australis (common reed) is important in water treatment, wetland habitat preservation and land reclamation in Afro-Eurasia.
Grasses are the primary plant used in lawns, which themselves derive from grazed grasslands in Europe. They also provide an important means of erosion control (e.g., along roadsides), especially on sloping land.
Although supplanted by artificial turf in some games, grasses are still an important covering of playing surfaces in many sports, including football (soccer), tennis, golf, cricket, softball and baseball.
Ornamental grasses, such as perennial bunch grasses, are used in many styles of garden design for their foliage, inflorescences, seed heads, and slope stabilization. They are often used in natural landscaping, xeriscaping, contemporary or modern landscaping, wildlife gardening, and native plant gardening.
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Grasses have long had significance in human society. They have been cultivated as feed for domesticated animals for up to 10,000 years, and have been used to make paper since the second century AD.[citation needed] Also, the primary ingredient of beer is usually barley or wheat, both of which have been used for this purpose for over 4,000 years.[citation needed]
Some common aphorisms involve grass. For example:
A folk myth about grass is that it refuses to grow where any violent death has occurred.[17]
See the full list of Poaceae genera.
Leaves of Poa trivialis showing the ligules
Bamboo stem and leaves, nodes are evident
A Chasmanthium latifolium spikelet
Wheat spike and spikelet
Spikelet opened to show caryopsis
Harestail grass
Grass
Sugarcane (Saccharum officinarum)
Roots of Bromus hordeaceus
Barley mature spikes (Hordeum vulgare)
Illustration depicting both staminate and pistillate flowers of maize (Zea mays)
A grass flower head (meadow foxtail) showing the plain-coloured flowers with large anthers.
Anthers detached from a meadow foxtail flower
Setaria verticillata, bristly foxtail
Setaria verticillata, bristly foxtail
Oryza sativa, Kerala, India
|coauthors= (help)| Wikimedia Commons has media related to Poaceae. |
| Wikispecies has information related to: Poaceae |
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| リンク元 | 「grass」「Alopecurus」「rice」「イネ科」「Gramineae」 |
[★] スズメノテッポウ属、アロペクルス属、Alopecurus属