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Adaptive Significance of Ray Corollas in Helianthus grosseserratus (Compositae)

Tod F. Stuessy, David M. Spooner and Kayleen A. Evans
The American Midland Naturalist
Vol. 115, No. 1 (Jan., 1986), pp. 191-197
DOI: 10.2307/2425849
Stable URL: http://www.jstor.org/stable/2425849
Page Count: 7
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Adaptive Significance of Ray Corollas in Helianthus grosseserratus (Compositae)
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Abstract

A major concern in plant evolution is to what extent morphological features are adaptive. Determining the value of a particular character state requires: (1) an hypothesis for the function of the character, and (2) a prediction and suitable test. An example of this approach in Compositae deals with ray corollas of Helianthus grosseserratus. Because the ray florets are neuter (i.e., do not set seed), the hypothesis is that the corollas function to attract pollinators to the disc florets. If the rays are removed, then fewer pollinators should be attracted. The prediction was tested in control (rayed) and experimental (rayless) populations directly by observing pollinator visits and indirectly by determining seedset. Four seasons of fieldwork have shown that: (1) frequency of visitation of pollinators was 61% lower for rayless populations, and the diversity of pollinators dropped sharply; and (2) seedset in rayless populations was 64% lower than for the rayed population. These data are consistent with the hypothesis that the ray corollas in H. grosseserratus serve to attract pollinators and that the structures are adaptive.

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