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(Last Modified On 6/14/2013)
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(Last Modified On 6/14/2013)
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Genus
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Parthenium L.
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PlaceOfPublication
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Sp. P1. 988. 1753
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Note
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LECTOTYPE: P. hysterophorus L.
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Description
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Bitter, aromatic herbs or shrubs; stems terete to slightly ridged. Leaves alternate, entire to highly divided. Inflorescence with heads solitary or in terminal corymbs or panicles. Heads radiate; involucre biseriate, each series of 5 bracts; receptacle paleaceous; ray florets 5, fertile, the ligules white, the corollas and styles persistent at apex of matured achenes; disc florets perfect but sterile, all except those of the outer row falling together as a unit, the corolla tubular, 5-lobed, the anthers with white or yellow pollen. Fruit an "achene complex" (Rollins, 1950), the achenes obcompressed, rounded to somewhat keeled on the inner face, puberulent, the margins thickened into riblike structures which are attached to a contiguous pair of infertile disc florets and a subtending inner involucral bract, the achene and attached florets and bract falling together at maturity; pappus of 2-3 awns or scales or absent. Chromosome base numbers x = 12, 17 and 18.
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Habit
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herbs or shrubs
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Distribution
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a genus of 16 species distributed throughout the western hemisphere, but has the highest concentration of taxa in Mexico.
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Note
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Two species, P. cinaraceum Rollins and P. glomeratum Rollins, are known from as far south as Argentina. One of the species of Parthenium, P. argentatum A. Gray ("guayule"), was cultivated in the southwestern United States as a potential alternate source of natural rubber during World War II. As a result of this economic potential, numerous investigations have been conducted upon many aspects of the species (anatomy, chemistry, etc.), and most of these publications are summarized in Hammond & Polhamus (1965). Traditionally, Parthenium has been placed in the subtribe Melampodiinae. In the present treatment, however, which follows the recent suggestions of Stuessy (1973), the genus is regarded as belonging to the Ambrosiinae.
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Reference
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Hammond, B. L. & L. G. Polhamus. 1965. Research on Guayule (Parthenium argentatum): 1942-1959. Tech. Bull. U.S.D.A. 1327: 1-157. Rollins, R. C. 1950. The guayule rubber plant and its relatives. Contr. Gray Herb. 172: 1-72. Stuessy, T. F. 1973. A systematic review of the subtribe Melampodiinae (Compositae, Heliantheae). Contr. Gray Herb. 203: 65-80.
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