|
The Poaceae (English pronunciation: ) (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 , following the Asteraceae, Orchidaceae, Fabaceae, and Rubiaceae.〔(【引用サイトリンク】author=Stevens, P.F )〕 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. == Description == 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「poaceae」の詳細全文を読む スポンサード リンク
|