Pollination and factors limiting fruit set of chasmogamous flowers of an amphicapric annual,Polygonum thunbergii (Polygonaceae) |
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Authors: | Kuniyasu Momose and Tamiji Inoue |
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Institution: | (1) Center for Ecological Research, Kyoto University, Shimosakamoto 4, 520-01 Otsu, Japan |
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Abstract: | Summary We observed phenology and insect visitors of chasmogamous flowers of an amphicarpic annual,Polygonum thunbergii (Polygonaceae) in Kyoto, Japan, and clarified limiting factors for fruit set by bagging and hand-pollination experiments.
Flowering season was one month from late September. Flowers were visited by various insect groups (total 30 families and 64
species) and effective pollinators were lower bees (Halictidae) and wasps (Vespidae) in the early flowering season, and middle-sized
flies (Syrphidae and Calliphoridae) in the later season. Nectar was secreted at a constant rate (0.013mg sugar/hour) throughout
a day and >90% of it was consumed by insects. The average number of flowers per ramet was 122, of which 95% were pollinated
in the natural conditions. Bagging experiments showed that 47% of flowers were self-pollinated even under no pollinator visits.
Despite of a high probability of cross pollination, the probability of fruit set within the ramet was 0.30 due to resource
limitation. We discussed possible adaptive significance of cleistogamous flowers under the condition that seeds could be produced
by chasmogamous flowers through self-pollination even under pollinator limited conditions. |
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Keywords: | Polygonum thunbergii Polygonaceae amphicarpic plant chasmogamous and cleistogamous flowers pollination ecology fruit set resource limitation pollinator limitation |
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