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''Pyrethrum'' was a genus of several Old World plants now classified as ''Chrysanthemum'' or ''Tanacetum'' (e.g., ''C. coccineum'') which are cultivated as ornamentals for their showy flower heads. Pyrethrum continues to be used as a common name for plants formerly included in the genus ''Pyrethrum''. Pyrethrum is also the name of a natural insecticide made from the dried flower heads of ''Chrysanthemum cinerariifolium'' and ''Chrysanthemum coccineum''. ==Description== Some members of the ''Chrysanthemum'' genus, such as the following two, are placed in the ''Tanacetum'' genus instead by some botanists. Both genera are members of the daisy (or aster) family, Asteraceae. They are all perennial plants with a daisy-like appearance and white petals. *''T. cinerariifolium'' is called the Dalmatian chrysanthemum, denoting its origin in that region of the Balkans (Dalmatia). It looks more like the common daisy than other pyrethrums do. Its flowers, typically white with yellow centers, grow from numerous fairly rigid stems. Plants have blue-green leaves and grow to 45 to 100 cm in height. The plant is economically important as a natural source of insecticide. The flowers are pulverized and the active components, called pyrethrins, contained in the seed cases, are extracted and sold in the form of an oleoresin. This is applied as a suspension in water or oil, or as a powder. Pyrethrins attack the nervous systems of all insects, and inhibit female mosquitoes from biting. When present in amounts less than those fatal to insects, they still appear to have an insect repellent effect. They are harmful to fish, but are far less toxic to mammals and birds than many synthetic insecticides and are not persistent, being biodegradable and also decompose easily on exposure to light. They are considered to be amongst the safest insecticides for use around food. Kenya produced 90% (over 6,000 tonnes) of the world's pyrethrum in 1998, called ''py'' for short. Production in Tanzania and Ecuador is also significant. Currently the world's major producer is Tasmania, Australia. *''C. coccineum'', the Persian chrysanthemum, is a perennial plant native to Caucasus and looks somewhat like a daisy. It produces large white, pink or red flowers. The leaves resemble those of ferns, and the plant grows to between 30 and 60 cm in height. The flowering period is June to July in temperate climates (Northern Hemisphere). ''C. coccineum'' also contains insecticidal pyrethrum substances, but it is a poor source compared to ''C. cinerariifolium''. *Other species, such as ''C. balsamita'' and ''C. marshalli'', also contain insecticidal substances, but are less effective than the two species mentioned above. 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「pyrethrum」の詳細全文を読む スポンサード リンク
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