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Plant Ecology

, Volume 184, Issue 1, pp 75–87 | Cite as

Petal movement in cape wildflowers protects pollen from exposure to moisture

  • A. Von Hase
  • R.M. Cowling
  • A.G. Ellis
Article

Abstract

We investigated diurnal patterns of petal movement (upright and reflexed) and sensitivity of pollen to moisture in a winter-flowering flora from the desert coast of Namaqualand, South Africa. Specifically, we tested the hypothesis that nocturnal flower closure associated with upright petal movement affords protection to pollen from winter precipitation. The proportion of open flowers in eight species from seven genera and three families, increased rapidly above air temperatures of about 20 °C. Flower temperature explained most of the variance in petal status. About 90% of the variance in flower temperature was explained by air temperature while radiation, wind speed and relative humidity had no significant independent effect. Petal opening was more closely correlated with temperature than the closing response, which may be under the additional control of endogenous factors. Pollen exposed to moisture overnight had a significantly higher frequency of damaged grains than control pollen in the majority of study species within the Aizoaceae and Neuradeceae. We found no evidence that pollen of asteraceous species exhibiting flower closure is sensitive to moisture. We conclude that pollen damage and the reduction in male fitness that may result from exposure to rain, dew and fog has provided an important selective impetus for the widespread evolution of upright petal movement and associated flower closure found among more than 3500 species in the predominantly winter and spring flowering Cape fynbos and succulent karoo floras.

Keywords

Fynbos flora Flower closure Flower temperature Petal movement Pollen damage Succulent karoo flora Winter-rainfall desert 

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Notes

Acknowledgements

The authors thank Bruce Anderson and Jan Vlok for valuable discussion, Shirley Pierce for comments on the manuscript, Jonathan Colville and Michael Raine for help in the field, and Henry Botha for technical assistance. Funding from the National Research Foundation’s Sustainable Environment Programme and the Mazda Wildlife Fund is gratefully acknowledged.

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Copyright information

© Springer Science+Business Media, Inc. 2005

Authors and Affiliations

  1. 1.Leslie Hill Institute for Plant ConservationUniversity of Cape TownRondeboschSouth Africa
  2. 2.Terrestrial Ecology Research Unit, Department of BotanyUniversity of Port ElizabethPort ElizabethSouth Africa
  3. 3.Department of Ecology and Evolutionary BiologyIrvineUSA

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