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Intraseasonal Variation in Seed Production Among Flowers and Plants of Thalictrum thalictroides (Ranunculaceae)
Anne E. Lubbers and Norman L. Christensen
American Journal of Botany
Vol. 73, No. 2 (Feb., 1986), pp. 190-203
Published by: Botanical Society of America, Inc.
Stable URL: http://www.jstor.org/stable/2444172
Page Count: 14
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Intraseasonal variation in ovule and seed production per flower and per plant of the perennial herb Thalictrum thalictroides (L.) Eames and Boivin was documented at three sites during three spring flowering seasons. Shading and pollen-addition experiments were used to assess the impact of variation in pollination and light availability on seed production. Mean seed number and percent seed set were lower in flowers open late in the season than in those open earlier. The lower percent seed set occurs primarily in flowers that are positioned laterally on the inflorescence and which open later than center flowers. Plants flowering early in the season produce more flowers, ovules and seeds than those flowering later. Mean percent seed set per plant did not change, however, indicating that temporal differences in total seed output can be traced largely to variation in total ovule number. Seed production may be limited by lack of pollination during periods of inclement weather. At least late in the season, seed output may also be resource-limited: the decline in percent seed set among flowers coincided with the decline in light availability, and hand-pollination of late-opening flowers did not increase percent seed set to earlier levels. Artificial shading led to a significant reduction in percent seed set of lateral flowers, and decreased the probability of flowering again the following year. Thus, the relative selective roles of resource and pollination limitations may vary during the flowering season.
American Journal of Botany © 1986 Botanical Society of America, Inc.