pyrethrum(redirected from pyrethrums)
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pyrethrum(pīrē`thrəm): see chrysanthemumchrysanthemum
, name for a large number of annual or perennial herbs of the genus Chrysanthemum of the family Asteraceae (aster family), some cultivated in Asia for at least 2,000 years.
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a genus of pubescent, perennial herbaceous plants of the family Compositae. The plants range in height from 5 to 150 cm. The alternate leaves are pinnatifid or, less frequently, entire. The small flowers are in heads, which are solitary or in two to 40 (less frequently, 100) corymbose inflorescences. The ray flowers are pistillate and ligulate, and the disk flowers are bisexual and tubular.
There are about 100 species of Pyrethrum, distributed in Europe (except the Far North), Asia, and North Africa. The USSR has approximately 55 species, found mostly in southern and mountainous regions. Some species accumulate pyrethrins —substances that are poisonous to insects and other invertebrates.
Two closely related species are cultivated: P. roseum (formerly P. carneum) and P. coccineum (formerly P. roseum). They grow in meadows and on the rocky slopes of the Caucasus, at elevations of 1,500 to 3,000 m. P. roseum, an herbaceous plant measuring 20 to 60 cm tall, has one or, less commonly, two or three flower heads. The leaves are not deeply pinnatifid, and the ray flowers are pink. The achenes, which are 2–3 mm long, are elongate and ribbed; they have a small crown. P. coccineum differs from P. roseum by its twice pinnatifid leaves. The ray flowers are pink or red. Both species contain substances in their inflorescences, stems, and leaves that have high insecticidal properties but are harmless to warm-blooded animals, including man. The Dalmatian pyrethrum (P. cinerariifolium) is cultivated as a source of insecticide. (It sometimes escapes cultivation.) The plant, which is native to the mountains of the Balkan Peninsula, is herbaceous and reaches a height of 15–45 cm. It has silvery gray twice or thrice pinnatifid leaves. The ray flowers are white or yellowish. The costomary (P. balsamita) is sometimes used as a source of insecticide, and the feverfew (P. parthenium), mainly varieties with yellow-green leaves, is used as a border ornamental. The genus Pyrethrum is often combined with the genera Leukanthemum and Chrysanthemum.
REFERENCEFlora SSSR, vol. 26. Moscow-Leningrad, 1961.
T. G. LEONOVA