Narcissus , the daffodil genus, exhibits an unusual diversity of sexual systems, with populations that are monomorphic, dimorphic or trimorphic for style length. Associated with this variation are striking differences among species in floral morphology and pollination biology. This diversity provides an opportunity to investigate the evolution of mating polymorphisms, and to determine how floral morphology promotes transitions among sexual systems. Because of the absence of heteromorphic incompatibility in Narcissus , floral morphology plays a key role in governing patterns of outcrossed mating. Phylogenetic evidence indicates that stylar monomorphism is ancestral in the genus, with multiple origins of stylar polymorphism, including independent origins of stigma-height dimorphism, distyly and tristyly. Sexual polymorphisms have evolved only in lineages with narrow floral tubes that are pollinated by Lepidoptera and/or long-tongued bees. Populations of polymorphic Narcissus species are typically dominated by the long-styled morph and display imperfect reciprocity in the positions of sexual organs. These features are consequences of the unusual association between stylar polymorphism and a self-incompatibility system that permits intramorph mating.

Most flowers are bisexual in function, but counting secondary allocation to attractive structures such as the corolla as equally male and female leads to the paradoxical conclusion that plants bearing perfect flowers invariably allocate much more to female than to male function. A method of calculating the gender of secondary floral allocation is described, and it is speculated that this allocation is predominantly male. Observations and experiments with natural populations of herbs, designed to test this hypothesis gave the following major results. (i) Insects visit larger flowers more frequently (Fragaria), and removal of floral biomass causes a reduction in the frequency of insect visits proportional to the fraction of biomass removed (Impatiens). (ii) Removal of attractive structures may cause a decline in the probability that a fruit will be formed but has no effect on the number of seeds set per fruit; thus, mutilation of essentially solitary flowers has no effect on seed-set per fruit (Impatiens), while removal of flowers from inflorescences in a species that forms several many-seeded fruits per inflorescence reduces fruit-set per inflorescence but has no effect on seed-set per fruit (Asclepias), and removal of sterile flowers from an inflorescence in which the fertile flowers yield one-seeded fruits is effective in reducing seed-set per inflorescence (Viburnum). (iii) Larger flowers may disperse a greater fraction of their pollen in unit time (Impatiens) and the removal of flowers from inflorescences causes a steep reduction in total pollen exported and a weak decline in the quantity of pollen exported per flower (Asclepias). These results are consistent with the hypothesis that a single insect visit (or a very few visits) suffices to fertilize almost all available ovules and is procured by a very small allocation to attractive structures, while much greater allocation is necessary to procure the numerous visits required to disperse a large fraction of the pollen. This inference is supported by a comparative survey of sexually dimorphic plants, in which male flowers are generally larger than female flowers, male inflorescences bear more flowers, and male plants bear more inflorescences. It is concluded that the flower is primarily a male organ, in the sense that the bulk of allocation to secondary floral structures is designed to procure the export of pollen rather than the fertilization of ovules. This conclusion may be sensitive to whether it is the flower or the inflorescence as a whole that represents the primary unit of attraction to insects. It was found that the performance of a given flower was substantially affected by other flowers in the same compact inflorescence (Asclepias), though not by other inflorescences on the same plant nor by those borne by nearby plants (Fragaria, Impatiens). A general quantitative theory of flower and inflorescence design is outlined, and used to organize the extensive experimental results for Asclepias.

090004 Intraspecific variation in pollen deposition and number of pollen tubes per style is rarely quantified, but is essential for assessing the occurrence of pollen limitation and pollen competition and their evolutionary implications. Moreover, pollen deposition, pollen tube growth, and the fate of fertilized ovules are rarely distinguished in field studies. Here we present such a study in eight natural populations of Prunella grandiflora . 090004 We quantified microgametophyte population sizes and inferred pollen limitation when the number of fertilizable ovules exceeded pollen tubes, and assessed seed set and fate after open pollination. 090004 Two and three populations had on average significantly fewer pollen grains and pollen tubes per flower, respectively, than the fixed number of fertilizable ovules per fruit, while one population experienced significant pollen competition. Style length was positively correlated with the number of pollen tubes. While pollen availability was very variable, seed abortion was significantly less frequent in denser populations, and in one population the proportion of well-developed seeds was significantly, positively correlated with the number of pollen tubes in the style. 090004 Less pollen deposition, lower numbers of pollen tubes reaching the base of the style, lower pollen quality and therefore increased abortion of fertilized ovules can all reduce seed set in natural P. grandiflora stands. Substantial intraspecific variability implies that microgametophyte competition also occurs in this species. Finally, style morphology may affect pollen receipt.

I measured phenotypic selection of floral traits through both male and female functions of the hermaphroditic flowers of Ipomopsis aggregata (Pursh) V. Grant su...

The invariability of animal-pollinated flowers relative to vegetative organs, such as leaves, suggests that these flowers may have been finely tuned for an optimum pollination performance. The evolutionary mechanism that could optimize and conserve a species' flower architecture is stabilizing selection, which occurs when intermediate phenotypes attain the highest fitness. Evidence for the operation of such a mechanism is rare in this context, however. Here, I report an experiment that used oil-seed rape (Brassica napus cv. Westar) as the basis of a model system in which the spatial disposition of flowers' sexual organs was manipulated in order to characterize the relationship between form and function. Specifically, individual flowers were manipulated by replacing a section of the style with a length of fine wire in order to produce flowers with pistils of various lengths. The pollination performance of these virgin, model flowers was then assessed by measuring the amount of pollen removed and deposited during a single bumblebee visit. There was no evidence that pollen removal was affected by pistil length. Variation in pistil length, however, was associated with a pronounced optimum in pollen deposition, which was attained by only a narrow range of pistil variants of intermediate length. These results suggest that stabilizing selection may maintain the architectural invariability of animal-pollinated flowers.

The commonly observed proximal-to-distal decrease within inflorescences of fruit and/or seed maturation per flower has frequently been attributed to competition among developing fruits for resources. The research summarized in this review suggests, however, that the observed variation can also be due to architecture--that is, to sources of variation inherent in plant axes. Thus, the fate of a developing flower depends not only on the reproductive events that have preceded it during the ontogeny of the organism, but on where it occurs within the architecture of an individual. The effects of architecture are separable experimentally from the effects of differential resource allocation, and careful experimental analysis of these two factors will enhance our understanding of the physiological, developmental, and evolutionary controls of fruit and seed production in flowering plants.

Floral form and function commonly vary quantitatively and qualitatively within inflorescences. Overall floral size, the sizes of individual floral organs, and the frequency of successful fruit and/or seed maturation may decline distally within inflorescences. These frequently observed patterns of variation have been attributed to competition for limited resources among developing flowers and fruits. The variation, however, can also be due to architecture, that is, to sources of variation inherent in plant axes. Floral morphology may change with position on an inflorescence axis, even in the absence of resource competition. Experimental analyses of Solanum hirtum and Arabidopsis thaliana identify the separate effects of architectural and resource limitation on floral development and morphology. The effects of architecture may mimic, mask, or lead to misinterpretation of the effects of resource competition on floral form. Floral morphology and function may be characterized as ontogenetically contingent: the morphology and fate of a developing flower depend on the events that have preceded it during the ontogeny of the organism and on where it occurs within the architecture of the individual. Careful consideration of the role of ontogenetic contingency in diverse taxa will be required to fully understand patterns of variation in floral morphology and function within individuals and may ultimately enhance our understanding of morphological diversification among taxa.

In angiosperm reproduction, pollen tubes elongate from the stigma through the stylar transmitting tissue to the ovary to deliver the male gametes for fertilization. This article reviews different forms of pollen tube transmitting tracts within the style as well as possibilities for bridging the gap from the transmitting tissue to the ovule. The pollen tube transmitting tissue is the place of possible pollen tube competition. Often the number of pollen grains deposited onto the stigma or stigmata of a flower exceeds the number of ovules in the ovary of the pollinated flower. In the styles of most taxa investigated, a reduction in number of the pollen tubes occurs from the stigma to the ovary (pollen tube attrition): the pollen tubes compete for entry into the embryo sac of the ovules within the ovary. A prediction of the extent of pollen tube competition can be partially equated to the P-S/O ratio. This ratio relates the total number of pollen grains (P) deposited onto the stigmata (S) at the end of the female phase of anthesis (stigma receptivity) to the number of ovules (O) present in the ovary. Some quantitative data on pollen load on the stigma or stigmata and resulting pollen tube competition will be demonstrated especially in the choricarpous gynoecium of Geum rivale (Rosaceae) and in the coenocarpous gynoecium of Cichorium intybus (Asteraceae). Data from this study are compared with data of other taxa obtained from the literature.

Abstract PREMISE OF THE STUDY: Two, nonmutually exclusive, mechanisms-competition for resources and architectural constraints-have been proposed to explain the proximal to distal decline in flower size, mass, and/or femaleness in indeterminate, elongate inflorescences. Whether these mechanisms also explain unusual positional effects such as distal to proximal declines of floral performance in determinate inflorescences, is understudied. METHODS: We tested the relative influence of these mechanisms in the andromonoecious wild olive tree, where hermaphroditic flowers occur mainly on apical and the most proximal positions in determinate inflorescences. We experimentally increased the availability of resources for the inflorescences by removing half of the inflorescences per twig or reduced resource availability by removing leaves. We also removed the apical flower to test its inhibitory effect on subapical flowers. KEY RESULTS: The apical flower had the highest probability of being hermaphroditic. Further down, however, the probability of finding a hermaphroditic flower decreased from the base to the tip of the inflorescences. An experimental increase of resources increased the probability of finding hermaphroditic flowers at each position, and vice versa. Removal of the apical flower increased the probability of producing hermaphroditic flowers in proximal positions but not in subapical positions. CONCLUSIONS: These results indicate an interaction between resource competition and architectural constraints in influencing the arrangement of the hermaphroditic and male flowers within the inflorescences of the wild olive tree. Subapical flowers did not seem to be hormonally suppressed by apical flowers. The study of these unusual positional effects is needed for a general understanding about the functional implications of inflorescence architecture. 2017 Botanical Society of America.

用过氧化氢酶法测定蒙古扁桃花粉的活力和寿命,用联苯胺-过氧化氢法测定柱头可授性.结果表明,蒙古扁桃 花粉活力在散粉后第2天最高,3 d后活力迅速下降,三种类型的植株的花粉活力下降速度存在差异,其活力可持续30 d左右.短柱头植株柱头在开花后1 d可分泌黏液,长柱头和中柱头花植株的柱头在开花后2 d才分泌黏液,短柱头分泌黏液的持续时间较后者长.柱头可授性持续时间同种之间也存在差异,长柱头和中柱头植株可达6 d,而短柱头花植株可持续10 d左右.

用过氧化氢酶法测定蒙古扁桃花粉的活力和寿命,用联苯胺-过氧化氢法测定柱头可授性.结果表明,蒙古扁桃 花粉活力在散粉后第2天最高,3 d后活力迅速下降,三种类型的植株的花粉活力下降速度存在差异,其活力可持续30 d左右.短柱头植株柱头在开花后1 d可分泌黏液,长柱头和中柱头花植株的柱头在开花后2 d才分泌黏液,短柱头分泌黏液的持续时间较后者长.柱头可授性持续时间同种之间也存在差异,长柱头和中柱头植株可达6 d,而短柱头花植株可持续10 d左右.

传地生物学是研究与传粉事件有关的种种生物学特性及其规律的一门学科，是植物生殖生态学和进化生物学关注的焦点之一，概述了近年来的主要研究热点及其进展，包括植物性表达的多样性及其进化、传粉者与花部特征的相互作用及其进化机制、传粉系统的进化、花粉竞争的生物学含义、花粉流的标记方法及散布规律的研究等５个方面，介绍了中国传粉生物学研究的现状及不足之处，结合国际上的发展趋势已由观察的、静态的描述传粉现象的阶段过

传地生物学是研究与传粉事件有关的种种生物学特性及其规律的一门学科，是植物生殖生态学和进化生物学关注的焦点之一，概述了近年来的主要研究热点及其进展，包括植物性表达的多样性及其进化、传粉者与花部特征的相互作用及其进化机制、传粉系统的进化、花粉竞争的生物学含义、花粉流的标记方法及散布规律的研究等５个方面，介绍了中国传粉生物学研究的现状及不足之处，结合国际上的发展趋势已由观察的、静态的描述传粉现象的阶段过

090004Despite an abundance of theory, few empirical studies have explored the ecological and evolutionary consequences of sex. We used a comparative phylogenetic approach to examine whether transitions between sexual and asexual reproduction are associated with changes in the size and distribution of species' geographical ranges, and their investment in reproduction.090004Here, we reconstructed the phylogeny of the genus Oenothera sections Oenothera and Calylophus (Onagraceae), which contain 35 sexual and 30 functionally asexual species. From each species, we collected data on the geographical distribution and variation in plant traits related to reproduction.090004Functionally asexual species occurred at higher latitudes, but did not differ in range size, compared with sexual species. Transitions to asexuality were associated with decreased investment in floral structures, including the length of petals, floral tubes and styles. Decreased anther size and increased seed size within asexual species also suggest altered allocation to male and female fitness.090004The observed range shifts are consistent with superior colonization of environments by asexual species following glaciation, and the observed changes in reproductive allocation support predictions made by models relating to the evolution of selfing. Our results suggest that the evolutionary consequences of asexual reproduction might be less restrictive than previously thought.

AbstractThe literature supports a positive correlation between pollen size and style length and that pollen size may be affected by a trade-off with pollen number. A correlation between pollen size and pollinator type has been hypothesized by some authors but not confirmed. To assess these associations, pollen grain number, pollen grain diameter and style length were measured in 53 species of Caryophylloideae that had been classified beforehand as being diurnal, nocturnal or self-pollinated. Surprisingly, many species showed two, and a few even three, distinct pollen grain size classes per individual anther. Therefore, further analyses were based on the different pollen size classes and respective pollen grain numbers. Firstly, we found no indication of a trade-off between pollen size and number. Secondly, a positive linear correlation between style length and pollen grain diameter was found using conventional analysis methods and phylogenetically independent contrasts. Thirdly, when using conventional analysis methods a strong relationship between style length and pollination mode was found, with nocturnal species having significantly longer styles and larger pollen grains than diurnal and selfing species. These results were not supported, however, when calculating comparisons of phylogenetically independent pairs. We discuss our findings in relation to intra-specific pollen polymorphism and pollen degeneration, both of which have been associated with different pollen grain sizes in Caryophylloideae. Furthermore, we discuss the possibility that pollen polymorphism might be a mixed strategy to optimise the success of pollen grains deposited at different pollen vule distances on long styles.

During the fertilisation process in plants, pollen tube growth rate may be selected as a trait important in male to male competition. Since female morphology provides the necessary selective arena for such competition, we investigate if sexual selection theory can be used to explain the evolution of pistil length as a female choice mechanism. This choice is performed by direct interference with male to male competition. Furthermore, the sessile nature of plants limits the number of mates a female can choose between, which could limit the benefit a female can gain from distinguishing between donors. To mirror these circumstances, we model a situation when there are only two competitors at a time. Using a game theoretical approach we show that if pollen tube growth rate can be used as an indication of heritable quality, pistil length can be selected in response to variation of this trait. We further find that length of the pistil affects selection of pollen tube growth rate. Thus female preference and male competitive ability co-evolve, but this does not necessarily lead to a positive relationship between the two. Under certain circumstances we find a negative relation instead. Given realistic differences in male quality, the model indicates that there is a potential for evolution of female morphology as a choice mechanism for pollen quality.

Abstract Variation in floral allocation within inflorescences has been attributed to resource competition and/or architectural effect. The two hypotheses were extensively studied and both hypotheses were partly supported by previous studies. However, the relative importance of resource competition and architectural effect may vary with stages of floral ontogeny in a species. To detect the effects of ontogenetic stages on floral variation, we manipulated the 6-flowered inflorescences of Adenophora jasionifolia (Campanulaceae) by early, late, and non-thinning flowers. Our results indicated that pollen and ovule production of the remaining flowers were not significantly different between early and late thinning manipulations, suggesting that floral sex allocation was determined far before flowering, in support of the architectural effect hypothesis. Under hand-pollination treatments, early thinning but not late thinning resulted in a significant increase in seed number and seed set of the remaining flowers. Therefore, the increase in seed production of the remaining flowers related to the floral ontogeny. The resource competition for floral allocation was significant under early thinning rather than late thinning manipulation. Our results suggest that studies on floral variation within inflorescences should take into account the stages of floral ontogeny.

It is postulated that in one reproductive session the level of maternal expenditure of an angiosperm plant is determined by a temporal series of controls on the number of potential fruit in which an investment is made. The serial adjustment hypothesis has three parts: A. The amount of maternal expenditure is regulated at many developmental units, particularly single flowers and fruit, at three principal sequential stages the determination of flowers, the development of ovaries and the maturation of fruit. B. At each stage, the initiation or continuation of an investment requires an amount of available resources above a certain threshold. Hence maternal expenditure is continually adjusted to the resources available at each developmental site. C. The pattern of controls that maximizes the maternal fitness of a plant is selected. Many factors affect the relative advantages of regulation at the three stages, therefore species and sexual morphs appear to vary widely in their proportional use of the three stages. Regulation of flower determination has the general advantages of offering bidirectional adjustment of maternal investment, maintaining a constant ratio of maternal to paternal investment, and reducing wasted expenditure. The later stages, ovary and fruit regulation, allow secondary adjustments of maternal investment in unpredictable circumstances and permit adjustment of the relative numbers of polliniferous and seminiferous flowers. The relative advantages of restricting the numbers of developing ovaries, or of maturing fruit, depend principally on the extent to which differences in the capacity of flowers to mature fruit are evident before anthesis.

多年来,不同繁育系统的榕树(Ficus spp.)的进化问题引起生物学家们极大的兴趣。前人通过对不同繁育系统榕树雌花的花柱长度、传粉榕小蜂产卵器长度和繁殖率的比较,推测榕树的雌雄异株是由雌雄同株进化而来的。为验证这一推论,选取雌雄同株的垂叶榕(Ficus benjamina)和钝叶榕(F.curtipes)以及雌雄异株的斜叶榕(F.tinctoria)和鸡嗉子榕(F.semicordata),进行了雌花花柱长度、传粉榕小蜂产卵器长度及繁殖率的比较。研究结果显示:1)两种雌雄同株榕树的传粉榕小蜂(Eupristina koningsbergeri和Eupristina sp.)的产卵器长度,显著长于两种雌雄异株榕树的传粉榕小蜂(Liporrhopalum gibbosae和Ceratosolen gravelyi)产卵器的长度,且雌雄同株榕树雌花花柱长度的变异大于雌雄异株雌花花柱长度的变异;2)两种雌雄同株榕树的雌花花柱长度呈单峰分布,且花柱长度的变异大于传粉榕小蜂产卵器长度的变异;两种雌雄异株榕树花序的雌花花柱长度呈双峰分布,雌花花柱长度的变异也大于传粉榕小蜂产卵器的长度变异;3)两种雌雄同株榕树的传粉榕小蜂产卵器长度能到达雌花子房的比例更高,可更有效地产生瘿花,而雌雄异株榕树产生种子的优势更强。研究表明:在传粉榕小蜂产卵器长度及花序雌花花柱分布方面,雌雄异株榕树有着明显的优势,但在繁殖率方面没有绝对优势。因此,前人从雌花花柱分布及繁殖率比较而做出榕树进化的推测并不正确。要真正解决榕树的进化问题,需要多学科、多指标的综合分析和深入研究。

多年来,不同繁育系统的榕树(Ficus spp.)的进化问题引起生物学家们极大的兴趣。前人通过对不同繁育系统榕树雌花的花柱长度、传粉榕小蜂产卵器长度和繁殖率的比较,推测榕树的雌雄异株是由雌雄同株进化而来的。为验证这一推论,选取雌雄同株的垂叶榕(Ficus benjamina)和钝叶榕(F.curtipes)以及雌雄异株的斜叶榕(F.tinctoria)和鸡嗉子榕(F.semicordata),进行了雌花花柱长度、传粉榕小蜂产卵器长度及繁殖率的比较。研究结果显示:1)两种雌雄同株榕树的传粉榕小蜂(Eupristina koningsbergeri和Eupristina sp.)的产卵器长度,显著长于两种雌雄异株榕树的传粉榕小蜂(Liporrhopalum gibbosae和Ceratosolen gravelyi)产卵器的长度,且雌雄同株榕树雌花花柱长度的变异大于雌雄异株雌花花柱长度的变异;2)两种雌雄同株榕树的雌花花柱长度呈单峰分布,且花柱长度的变异大于传粉榕小蜂产卵器长度的变异;两种雌雄异株榕树花序的雌花花柱长度呈双峰分布,雌花花柱长度的变异也大于传粉榕小蜂产卵器的长度变异;3)两种雌雄同株榕树的传粉榕小蜂产卵器长度能到达雌花子房的比例更高,可更有效地产生瘿花,而雌雄异株榕树产生种子的优势更强。研究表明:在传粉榕小蜂产卵器长度及花序雌花花柱分布方面,雌雄异株榕树有着明显的优势,但在繁殖率方面没有绝对优势。因此,前人从雌花花柱分布及繁殖率比较而做出榕树进化的推测并不正确。要真正解决榕树的进化问题,需要多学科、多指标的综合分析和深入研究。

Abstract PREMISE OF THE STUDY: One proposed function of long styles is to intensify selection among male gametophytes relative to short styles. If so, given sufficient competition, longer styles will have higher rates of pollen tube attrition (failure to reach the style base) within the style than shorter ones. Alternatively, style length may influence pollen receipt, which itself may affect attrition rates. METHODS: We tested these predictions by collecting senescing styles from wild populations of two insect-pollinated Clarkia species. We examined the number of pollen grains adhering to the stigma, length of styles, and rates of attrition from the stigma surface to the stigma-style junction (SSJ), from the SSJ to the style base, and from the stigma surface to the style base. Multivariate analyses estimated the independent effects of pollen grains per stigma, the number of pollen tubes at the SSJ, and style length on attrition. KEY RESULTS: Style length was generally positively correlated with pollen receipt, and the number of pollen grains per stigma was positively correlated with all three attrition rates. In neither species was any attrition rate affected by style length independent of the number of pollen grains per stigma. CONCLUSIONS: Pollen attrition was mediated by style length, but the function of style length was primarily to increase the number of germinating pollen grains, which affected attrition rates either through stigma clogging or pollen-pollen interactions. Style length may have a direct effect on pollen receipt due to the stigma's position relative to pollinator body parts, but traits correlated with style length may also directly affect pollen receipt. 2016 Botanical Society of America.

In order to estimate pollen tube attrition and to relate it to the breeding system, numbers of microgametophytes within the stigma and at the bottom of the style were scored in species of the Brassicaceae, 17 sporophytically self-incompatible, 11 predominant inbreeders, 4 facultative outcrossers. Attrition was evident in almost all species. The mean number of tubes at the bottom of the style, and mean number of stylar tubes per ovule were significantly lower in outbreeders. The degree of attrition, measured as "attrition rate" (the proportion of tubes in the stigma that do not reach the bottom of the style) was higher in outbreeders; it was positively correlated with the pollen: ovule ratios as estimates of the degree of outbreeding in the species involved. In outbreeders, sexual selection seems to be rather effective in inhibiting certain microgametophytic genotypes from reaching the ovules. Because of the low number of tubes per ovule in most cases, we assume that, in the Brassicaceae, female choice may be more effective in sexual selection and in ensuing pollen tube attrition.

The styles of flowers may represent an arena for pollen competition in the race to fertilize ovules. Accordingly, selection should favour a longer ‘race’ to better discriminate among variable pollen by increasing style length. Sampling across a taxonomically diverse range of wild and outcrossed species, we found that the distribution of style lengths within plants were skewed towards longer styles, as predicted. In self-pollinated domesticated species, where discrimination among pollen is less important, we found no such pattern. We conclude that style length is under directional selection towards longer styles as a mechanism for mate choice among pollen of variable quality.

AbstractTrithuriasubmersa. . . . submersa has been accompanied by predictable modifications to reproductive development, which, because of the ancient relationship between Hydatellaceae and all other angiosperms, suggests that traits underlying the lability of flowering plant post-pollination biology were present early in their history.

http://doi.wiley.com/10.1111/j.1469-8137.2011.03912.x

Abstract Flower color polymorphism is relatively uncommon in natural flowering plants, suggesting that maintenance of different color morphs within populations is difficult. To address the selective mechanisms shaping pollen-color dimorphism, pollinator preferences and reproductive performance were studied over three years in Epimedium pubescens in which some populations had plants with either green or yellow pollen (and anthers). Visitation rate and pollen removal and receipt by the bee pollinator ( Andrena emeishanica ) did not differ between the two color morphs. Compared to the green morph, siring success of the yellow morph's pollen was lower, but that of mixtures of pollen from green and yellow morphs was lowest. This difference, corresponding to in and ex vivo experiments on pollen performance, indicated that pollen germination, rather than tube growth, of the green morph was higher than that of the yellow morph and was seriously constrained in both morphs if a pollen competitor was present. A rare green morph may invade a yellow-morph population, but the co-existence of pollen color variants is complicated by the reduced siring success of mixed pollinations. Potential pollen competition between morphs may have discouraged the maintenance of multiple phenotypes within populations, a cryptic mechanism of competitive exclusion. This article is protected by copyright. All rights reserved

小花风毛菊（Saussurea paniflora）是菊科风毛菊属的一种多年生草本植物，是该属在青藏高原东缘的一个优势种。该文研究了小花风毛菊11个居群性器官的变异与11个海拔高度（2100～3500m）之间的相关性，以及花丝、花药长和花柱、花柱分枝长与花粉数之间的相关性；探讨了小花风毛菊的性器官是如何随海拔高度发生变异，如何与胁迫环境相适应，实现交配成功，提高繁殖成功率，使其成为该属植物“现代分布中心”的优势种。结果表明：1）花丝、花药长与海拔高度呈极显著的正相关关系（P〈0．01）；2）花粉数与海拔高度呈极显著的负相关关系（P〈0．01）；3）花柱、花柱分枝长及花柱分枝长和雌蕊长的比与海拔高度呈极显著的正相关关系（P〈0．01）；4）花柱、花柱分枝长和花丝长与花粉数呈显著的负相关关系（P〈0．05）；5）种子的成熟率与海拔高度呈显著的正相关关系（P〈0．05）。说明小花风毛菊种内性器官在特定的生存环境下发生了变异，特别是在花粉数随海拔的升高明显减少以及昆虫的多样性、丰富性和活动性明显降低的情况下，它能够通过花柱分枝长度的变异来提高柱头对传粉昆虫的感受性，能通过种子成熟率的提高来保证高海拔数目显著减少的种子的成功发育，进而在一定程度上导致了该物种繁殖成功率的上升，使它成为青藏高原这一胁迫环境中的优势种。

小花风毛菊（Saussurea paniflora）是菊科风毛菊属的一种多年生草本植物，是该属在青藏高原东缘的一个优势种。该文研究了小花风毛菊11个居群性器官的变异与11个海拔高度（2100～3500m）之间的相关性，以及花丝、花药长和花柱、花柱分枝长与花粉数之间的相关性；探讨了小花风毛菊的性器官是如何随海拔高度发生变异，如何与胁迫环境相适应，实现交配成功，提高繁殖成功率，使其成为该属植物“现代分布中心”的优势种。结果表明：1）花丝、花药长与海拔高度呈极显著的正相关关系（P〈0．01）；2）花粉数与海拔高度呈极显著的负相关关系（P〈0．01）；3）花柱、花柱分枝长及花柱分枝长和雌蕊长的比与海拔高度呈极显著的正相关关系（P〈0．01）；4）花柱、花柱分枝长和花丝长与花粉数呈显著的负相关关系（P〈0．05）；5）种子的成熟率与海拔高度呈显著的正相关关系（P〈0．05）。说明小花风毛菊种内性器官在特定的生存环境下发生了变异，特别是在花粉数随海拔的升高明显减少以及昆虫的多样性、丰富性和活动性明显降低的情况下，它能够通过花柱分枝长度的变异来提高柱头对传粉昆虫的感受性，能通过种子成熟率的提高来保证高海拔数目显著减少的种子的成功发育，进而在一定程度上导致了该物种繁殖成功率的上升，使它成为青藏高原这一胁迫环境中的优势种。