Floral morphology and reproductive success in the orchid Epipactis helleborine: regional and local across-habitat variation |
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Authors: | B K Ehlers J M Olesen J Ågren |
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Institution: | (1) Department of Ecology & Genetics, University of Aarhus, Aarhus C, Denmark, DK;(2) Department of Plant Ecology, EBC, Uppsala University, Uppsala, Sweden, SE |
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Abstract: | The terrestrial orchid Epipactis helleborine is a morphologically variable species with a wide distribution in Europe. It is pollinated by social wasps, and most populations
show the morphological characteristics of outcrossing species. However, local predominantly selfing subspecies and varieties
have been documented from drier habitats. To document geographic variation in floral morphology, ability to produce seeds
through autogamy, and reproductive success in E. helleborine, we sampled 13 populations from three geographic regions along a latitudinal gradient of c. 1000 km from northern to southern Sweden. In the southernmost region, populations in dry and mesic habitats were compared.
Supplemental hand-pollination was conducted to determine whether among-population variation in fruit set could be explained
by differences in the natural level of pollination, and whether any relationship between floral morphology and fruit production
could be explained by interactions with pollinators. Bagging experiments showed no evidence of autogamy in any of the study
populations. Number of flowers, pollinia removal and fruit set varied significantly among populations but did not differ among
regions. Pollinia removal was positively correlated with population size and both pollinia removal and fruit set were lower
in dry than in mesic habitats. At the level of the individual plant, the number of pollinia removed increased more rapidly
with flower number than did number of fruits produced. The hand-pollination experiment indicated that the positive relationship
between number of flowers and fruit production was due to a higher degree of pollen limitation in plants with few flowers
than in plants with many flowers. The experiment also showed that variation in the level of pollen limitation could only partly
explain variation in fruit set among populations.
Received November 6, 2001; accepted April 27, 2002 Published online: December 3, 2002 |
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Keywords: | : Epipactis helleborine floral display flower morphology fruit set hand-pollination pollen limitation pollen removal |
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