Am J Bot. 1998 Feb;85(2):235.
Gynomonoecy is the sexual system in which female and bisexual flowers occur on the same plant. This system has received little attention despite the considerable work on other plant sexual systems in the past few decades. Our study examines one hypothesized advantage of having two flower types on a plant, namely that this arrangement permits flexibility in allocation of resources to male and female reproductive functions. We examined 16 species of Aster (Asteraceae), a genus of gynomonoecious, perennial herbs. Plants in this genus produce heads consisting of a whorl of female flowers around a cluster of bisexual flowers. Among field-grown plants we found no evidence that plant size, date, position of heads, rainfall, or shade influenced the proportion of female flowers. A series of greenhouse experiments likewise revealed no large or consistent effects of light, nutrients, or position of heads on the proportion of ray flowers. While floral ratios proved very stable in the face of environmental and physiological variables, they exhibited significant variation among plants and among sibships in most species. We conclude that the presence of two flower types in gynomonoecious asters is not advantageous in permitting flexibility in allocation of resources to male and female functions. We believe that the advantage of the female flowers in aster heads lies either in reducing pollen-pistil interference or in attracting pollinators.
雌雄同体是一种性系统，其中雌性和两性花出现在同一植株上。尽管在过去几十年中对其他植物性系统进行了大量研究，但这个系统却很少受到关注。我们的研究考察了在植物上拥有两种花型的一个假设优势，即这种排列可以灵活分配资源用于雄性和雌性生殖功能。我们研究了 16 种紫菀属（菊科）植物，这是一个雌雄同体、多年生草本植物属。该属植物的头部由一圈雌性花围绕着一簇两性花组成。在田间生长的植物中，我们没有发现植物大小、日期、头部位置、降雨量或遮荫会影响雌性花比例的证据。一系列温室实验同样没有发现光照、养分或头部位置对射线花比例有大的或一致的影响。虽然在面对环境和生理变量时，花的比例非常稳定，但在大多数物种中，它们在植物之间和同系物之间表现出显著的变化。我们得出结论，雌雄同体紫菀属植物中存在两种花型并没有在资源分配上为雄性和雌性功能提供灵活性的优势。我们认为，紫菀属植物头部的雌性花的优势在于减少花粉-柱头干扰或吸引传粉者。
