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Parthenium Linnaeus. Wild Quinine.

Key to Parthenium

A genus of about 16 species, herbs and shrubs, of North America and the West Indies. The genus should be divided, based on multiple lines of evidence.

ID notes:Parthenium has five ray flowers per head, small scooplike white flowers set at the five radial points of a pentagon superimposed on the head; we key Parthenium as having ray flowers, but also key it as a "failsafe" as a composite lacking ray flowers, as the ray flowers are small and inconspicuous and likely to be overlooked as rays. These five ray flowers are the only flowers in each head that produce cypselas (the disc flowers are functionally staminate). Each cypsela, however, is shed as a unit consisting of the subtending phyllary, the two contiguous disc flowers, and the associated paleae of the two disc flowers.

Ref: Cronquist (1980); Mears (1975); Rollins (1950); Strother (2006ff) In Flora of North America Editorial Committee (2006c). Show full citations.

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