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The Morphology of the Inflorescence of Ragweeds (Ambrosia-Franseria: Compositae)

Willard W. Payne
American Journal of Botany
Vol. 50, No. 9 (Oct., 1963), pp. 872-880
Stable URL: http://www.jstor.org/stable/2439774
Page Count: 9
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The Morphology of the Inflorescence of Ragweeds (Ambrosia-Franseria: Compositae)
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Abstract

The ragweeds possess an inflorescence which is highly modified in relation to anemophily. Several trends from primitive to specialized character expressions may be seen in the morphology of the unisexual capitula and florets. An evolutionary scheme is resented whereby the catkinlike, acropetally maturing, staminate spike and the sessile, centrifugally developing, fruiting involucre cluster are derived from basic inflorescence types within the Compositae. Morphological evidence suggests that: (1) the taxa Ambrosia and Franseria should be combined under the older generic name Ambrosia; (2) the ragweeds and their relatives as a group appear to occupy a position intermediate between the Heliantheae and Anthemideae, as currently delimited within the Compositae.

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