AOBPreview originally published online on October 2, 2002
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Annals of Botany 90: 613-622, 2002
© 2002 Annals of Botany Company
Gender Variation of Sequential Inflorescences in a Monoecious Plant Sagittaria trifolia (Alismataceae)
1 College of Life Sciences, Wuhan University, Wuhan 430072, China and 2 Department of Livestock and Grassland Science, National Agricultural Research Center for Western Region, Shimane 694-0013, Japan
* For correspondence. E-mail hsq1971{at}affrc.go.jp or sqhuang2001{at}hotmail.com
Received: 21 January 2002; Returned for revision: 17 July 2002; Accepted: 28 July 2002 Published electronically: 2 October 2002
In protogynous plants, female flowers of early blooming plants are at a reproductive disadvantage because they cannot set fruit due to the lack of available pollen. To study this phenomenon, gender expression of the monoecious herb Sagittaria trifolia was investigated over the entire flowering season in two field and two cultivated populations in Hubei and Hunan Provinces, China. In racemes of S. trifolia, flowers open sequentially from bottom to top, with female flowers opening first followed by male flowers. This creates a temporal separation of sexes in the species. Under field conditions small plants are often male, with production of both male and female flowers increasing with plant size. Femaleness increased among sequential inflorescences since female flower production increased whereas male flower production did not. Seed production was greater in large inflorescences because they contain more female flowers, and the number of ovules increased in female flowers at basal positions within the raceme. A consistent pattern of high seed set was observed in flowers from both field and cultivated populations. About 1 % of unfertilized ovules resulted from no pollination and 2 % of the seeds produced were only partly developed due to resource limitation. In the first inflorescence of the six experimental populations, 6·7–40·0 % of individuals produced only male flowers, and female flowers of 1·9–6·5 % individuals were aborted. The occurrence of male flowers in early blooming inflorescences could be an adaptive strategy to conserve resources and enhance pollination of female flowers in protogynous S. trifolia.
Key words: Sagittaria trifolia, gender variation, sequential inflorescences, pollination, seed production, monoecy, dioecy, dichogamy.
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