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Gynomonoecy is the sexual system in which individual plants bear both female and bisexual flowers. Little attention has been paid to the adaptive significance of this sexual system, which is particularly prevalent in the Asteraceae. We investigated one hypothesized advantage of having two flower types, namely that this arrangement permits flexibility in allocation of resources to male and female reproductive functions. We examined six species of goldenrod (Solidago), a genus of gynomonoecious, perennial herbs. In greenhouse experiments, we varied one or more of three environmental variables - light, nutrients and water - and/or examined heads in different positions on the plants. Most variables had little or no effect on the proportion of ray flowers. Significant effects were found for light in 0 of 5 experiments, for nutrients in 4 of 9 experiments and for water in 0 of 3 experiments. Heads in different positions in the inflorescence differed in the proportion of ray flowers in half of the experiments, though the differences were small. We also monitored temporal patterns in four species and found that the proportion of ray flowers increased significantly over the blooming period and the number of flowers per head declined. Because of the small number of significant effects and their modest magnitude, we conclude that the presence of two flower types in goldenrods is probably not advantageous in allowing flexibility in sex expression. It seems likely that this sexual system has been more important either in increasing pollinator attraction or in reducing pollen-pistil interference. The small observed changes in floral ratios were generally accompanied by changes in disc size in a manner consistent with an explanation based on allometry. © 2002 The Linnean Society of London.



Published Article/Book Citation

ROBERT I. BERTIN, GREGORY M. GWISC, Floral sex ratios and gynomonoecy in Solidago (Asteraceae), Biological Journal of the Linnean Society, Volume 77, Issue 3, November 2002, Pages 413–422,