湿地植物大花百合种群的性系统特征

开花植物性系统特征是植物在长期适应进化过程中逐渐形成的繁殖策略, 它在一定程度上影响了物种的种群结构及其在生境中的分布格局, 因此性系统特征一直是植物进化与生态学领域的研究热点。本研究于2012年和2020年在吉林省金川泥炭沼泽湿地, 通过样地调查取样的方法, 研究了湿地植物大花百合(Lilium concolor var. megalanthum)的性系统特征以及不同性别表型植株的比例、密度及空间分布格局, 并探究了大花百合植株个体大小和其性别表达的联系, 比较了不同性别表型的花粉实际可育性和来源不同的花粉授粉处理结实后的种子活力。结果显示, 个体水平上, 大花百合具有雄花植株、两性花植株和雄花两性花同株(即雄全同株) 3种性表型; 种群水平上, 具有雄花的个体充当父本, 通过花粉向下一代传递基因, 而具有两性花的个体主要充当母本, 通过胚珠实现基因的传递。2020年大花百合雄花植株占种群内开花植株的39.14%, 相比2012年雄花植株比例增加了22.80%; 大花百合种群分布密度为0.06株/m², 较2012年下降了0.09株/m²。从2012年到2020年, 总体表现为种群密度降低, 雄花植株相对比例增加的趋势。两性花植株和雄花植株在小尺度范围主要呈聚集分布, 随着尺度增大, 趋于随机分布。雄花植株显著小于两性花植株, 但鳞茎资源分配显著高于两性花植株。大花百合植株的性表达遵循大小依赖的性分配假说: 个体较小的植株表达为雄花植株, 而个体较大的植株则为两性花植株或雄全同株。在不同授粉处理下的结籽率和种子萌发结果表明, 大花百合自花授粉结籽率和坐果率显著低于异花授粉, 雄花植株和两性花植株花粉可育性以及对两性花植株授粉后所获得种子活力无显著差异。大花百合雄花植株的出现可能是对有限环境资源条件适应的结果, 反映了湿地条件下该植物在生长和繁殖资源之间的权衡策略, 在长期的湿地演变过程中, 这种性系统特征的出现具有一定的适应性意义。     

澜沧舞花姜繁殖生物学特性及其进化意义探讨

 舞花姜属（Globba）植物具有多样的繁殖策略。分布于西双版纳的澜沧舞花姜（Globba lancangensis）自然条件下既能结实,同时又能在花序下部产生珠芽。通过对澜沧舞花姜的花部性状、花粉活力、传粉昆虫的访花行为、结实状况、珠芽产量等多方面的观测,初步了解了澜沧舞花姜的繁殖生物学特性。结果表明,澜沧舞花姜具有雄花及两性花同株的性表达特征。雄花及两性花的花粉在中午12∶00以前活力很高,之后雄花的花粉活力急剧下降,而两性花的花粉到16∶00仍有萌发能力。澜沧舞花姜在花序上产生雄花及两性花,每个花序每天仅开少量的花,其中50%的时间仅开雄花或两性花,在整个种群中形成了一定程度的暂时性的雄花两性花异株现象,从而增加了异交的可能性。澜沧舞花姜雄花的存在为P/O低的两性花提供了花粉补贴,这使得它可以通过调节雄花与两性花比例来调节种群的P/O,从而保证一定的结实能力。人工自交与异交下结果率没有差异,但自交结实率显著低于异交结实率,表明澜沧舞花姜有明显的自交不亲和现象。排蜂（Megapis dorstata）和黄绿彩带蜂（Nomia strigata）是澜沧舞花姜的主要访花昆虫,其中排蜂是它的有效传粉昆虫。澜沧舞花姜可能通过雄花两性花同株与自交不亲和相结合来促进异交。     

中国北亚热带油橄榄(城固32)开花生物学特性研究

为研究北亚热带内陆地区油橄榄（Olea europaea L.）开花物候、开花样式及花器官特征,探讨其有性繁殖系统的特点。试验对西秦岭南坡地区油橄榄（城固32）的开花生物学进行研究,统计开花进程,雄花和两性花在花序上的着生位置和数量,测定雄花和两性花形态指标并切片观察,电镜扫描分析雄花与两性花花粉粒。结果表明：（1）在北亚热带北缘内陆气候条件下油橄榄花期集中在5月,单株花期15~20 d,盛花期持续4~6 d;（2）油橄榄具有雄全同株的性系统且花器官较小,雄花及两性花都具有正常发育的雄蕊。通过制作石蜡切片观察,发现两性花的雌蕊正常发育,而雄花只有较小的子房和败育的柱头;（3）雌蕊是两种花型花器官生物量差异的主要部位,两性花雌蕊的生物量明显比雄花大（P<0.01）,树体分化出雄花投入的资源更少;（4）雄花与两性花在花粉量、花粉粒大小上差异不显著,在着生位置上,花序轴顶花全部为两性花,雄花出现在花序轴的中部和基部的几率分别是21.13%和30.77%。油橄榄品种城固32具有典型的雄全同株现象,雄花更倾向于在花序上出现的位置在行使它雄性功能方面并无优势可言,而且雄花花粉粒在数量、活力方面也没有优势,但是雄花的出现增加了花粉数量和P/O值,提高了植株的雄性适合度,雄花的出现也降低了两性花落花导致的树体资源浪费,保障其在资源有限的环境中能够繁殖最大化。     

雄全同株植物簇花芹花期性别分配与开花式样

簇花芹(Soranthus meyeri)是古尔班通古特沙漠中常见的、具雄全同株性系统的伞形科多年生早春短命植物。该文对簇花芹花期性比(两性花数/总花数)与植株大小的关系及其开花式样进行了研究, 重点对花期大小依赖的性别资源分配进行了讨论。结果表明: 2006-2008年簇花芹群体水平的性比分别为0.69 ± 0.03、0.62 ± 0.03和0.69 ± 0.02, 彼此间无显著差异( p > 0.05), 表明其性比是相对稳定的, 可能受遗传因素的控制。雄花生物量与花粉量均比两性花的小, 说明产生雄花比产生两性花所需资源少。一级复伞形花序比二级复伞形花序具有较多的两性花, 说明前者易从植株上获得资源用于增加雌性适合度; 而后者产生较多的雄花以避免在雌性功能上资源投入的浪费, 增大花展示以吸引更多传粉者来增加花粉输出总量, 提高其整体适合度。植株水平的性比与地上营养器官的生物量间呈正相关关系, 说明较大个体对雌性功能的投资较大, 雌性繁殖成功受资源限制。复伞形花序内各伞形花序几乎同时向心开放, 且所有两性花及花序均为雄性先熟, 雌雄阶段完全分离, 但一级复伞形花序比二级复伞形花序早开放约5天, 彼此开花重叠期约为1天。这些特征对于一级复伞形花序进行异株异花授粉以及植株内不同级别花序间的同株异花传粉、避免雌雄功能间的干扰具有重要意义。     

刺山柑雄全同株性系统的适应意义

对分布于新疆北部干旱荒漠区的刺山柑Capparisspinosa性系统进行了研究.结果表明:(1)该物种具有典型的雄全同株性系统.雄花和两性花的雄蕊均正常发育,且有长短之分;两性花的雌蕊发育正常,而雄花的雌蕊败育,只行使雄性功能.(2)居群间每天开放的雄花和两性花比率、两性花的长短雄蕊数及雄花短雄蕊的花丝与花药长等存在极显著差异(P<0.01),但花器官生物量没有显著差异(P>0.05).(3)单花花期为15-16 h,每天18:00时左右开始开放,有强烈的气味和花蜜产生.植株每天产生的雄花和两性花数是随机的,可形成短时的雄花与两性花异株,但居群内雄花数比两性花数多.(4)三个居群两性花的P/O值分别为1.57×104、1.65×104和1.71×104.居群内雄花和两性花的花粉数及长、短雄蕊花药的花粉数均无显著差异(P>0.05),居群间雄花和两性花的花粉数、两性花的胚珠数及P/O值差异也不显著(P>0.05).(5)各居群雄花和两性花长短雄蕊的花粉活力动态变化曲线相似,花粉寿命为18-20 h,两性花雌蕊柱头的可授期为16-18h.(6)访花昆虫为膜翅目Hymenoptera和鳞翅目Lepidoptera昆虫,3个居群共有7种访花昆虫,其活动受天气影响很大.(7)两性花不存在无融合生殖现象,授自花花粉、同株异花花粉和异株异花花粉后均可结实,属于混合交配系统.刺山柑的雄全同株性系统可能是在长期与荒漠环境相适应的过程中由遗传和环境共同作用的结果.雄花的出现不仅增加了花粉数和P/O值,提高了植株的雄性适合度,同时增加了花的数量、对传粉昆虫的吸引力以及两性花柱头接受异花花粉的机会,提高了异交率和雌性适合度,保障其在荒漠极端环境中繁殖成功.     

Polyploidization and sexual dimorphism of floral traits in a subdioecious population of Dasiphora glabra

银露梅亚雌雄异株种群的多倍化和花特征性二态 性二态是性别分离植物的常见性状,对植物的雌性和雄性功能可能产生不同的影响。本文以青藏高原特有植物银露梅(Dasiphora glabra)为研究对象,利用银露梅同时存在两性、雌性和雄性植株的种群,探讨银露梅与传粉相关的花特征性二态现象及其对传粉者访问、花粉流和结实的影响。另外,本文还利用流式细胞仪检查了两性植株、雄性植株和雌性植株之间基因组大小的差异。研究结果表明：银露梅雌性植株和雄性植株数量约占种群中植株总数量的40%,表明银露梅两性植株数量多于雄性和雌性的植株数量。两性植株的花数量显著多于雄性和雌性植株的花数量。雄花的花大小显著大于雌花和两性花的花大小。雄花的花粉数量与两性花的花粉数量没有差异,但是雌花的胚珠数量显著高于两性花的胚珠数量。双翅目的蝇类是银露梅最主要的访花者,尽管访花者偏好访问更大的花,但是在花间连续访问对大花没有表现出偏好。模拟花粉流实验表明,两性植株和雄性植株的有效花粉转移都很低,从而导致较低的结实率。雌性植株和雄性植株的DNA含量约为两性植株的4倍,并且单性植株和两性植株之间相互授粉不能结实。以上结果表明,与两性花相比,雌花和雄花在与传粉相关的花特征二态性上分别在雌性和雄性功能上表现出优势,但这种优势在很大程度上被低效的花粉转移所掩盖。银露梅的雌性植株和雄性植株经历了多倍化事件,导致与两性植株之间存在繁殖隔离,从而维持了3种性别植株的共存。     

雄全异株植物瘿椒树（省沽油科）的传粉生物学

从开花动态、传粉昆虫、花的形态结构、繁育系统、花粉活力和柱头可授性等方面研究了我国特有珍稀植物瘿椒树（Tapiscia sinensis Oliv.）的传粉生物学特性。瘿椒树是典型的雄全异株植物,两性花中含有功能性花粉,且自交亲和,但雄花花粉活力和萌发力是两性花的10倍以上。雄株和两性植株具有相同开花物候期,花期均为5月下旬至6月上旬,单花期为4-5天,雄花和两性花的5枚花药开裂的不同步性明显延长了散粉时间。两性花雌蕊先熟,柱头可授性较长。具有适应风媒和虫媒传粉的花部特征。传粉昆虫主要为蜜蜂科（Apidae）和食蚜蝇科（Syrphidae）昆虫,访花高峰期为8：30-10：30。维持瘿椒树雄全异株的可能机制是：雄株总体上增加了异交花粉的数量和质量;两性花的雄蕊为该物种提供了繁殖保障,同时为传粉者提供了报酬。     

细枝柃性别表达特性及资源分配

已有的资料将柃木属(Eurya)描述为严格的雌雄异株植物, 性别变异现象极为少见。目前仅在柃木(E. japonica)和钝叶柃(E. obtusifolia)等少数种类中报道过两性花的存在。近几年笔者发现细枝柃(E. loquaiana)存在性别变异现象, 性别变异株上具有不同性别类型的花。该文从单花和植株水平分析了细枝柃的性别表达特性, 并对不同类型花的花部构件生物量分配进行比较分析。结果表明, 细枝柃具有6种类型的花, 从单花水平上看, 细枝柃性别有雌性、雄性及两性3种类型; 细枝柃性别在植株水平上体现较为复杂, 有雌株, 雄株, 雌花和两性花同株, 雄花和两性花同株, 雌雄异花同株及雌花、雄花、两性花同株6种类型; 在细枝柃花部构件生物量分配中, 雄花(包括雄株花和变异株雄花)花部构件生物量分配中雄蕊生物量的分配低于雌花(包括雌株花和变异株雌花)中雌蕊生物量的分配; 两性花中, 雄蕊生物量分配低于雌蕊, 这是其优化资源分配的手段, 进而获取最大适合度收益。     

利用腊叶标本初探豹子花属植物的性表达及其与个体大小的关系

植物性系统进化过程中很少有植物通过雌性败育的方式实现性系统由联合走向分离,然而雄花在百合科植物中大量存在,引起了研究者的关注。本研究利用百合科豹子花属植物的腊叶标本,获取它们的花性别表型、花大小、株高以及分布海拔等信息探讨豹子花属植物的性表达样式,并对样本量较多的开瓣豹子花、云南豹子花、多斑豹子花和豹子花四个种的性表达及其与个体大小的关系进行分析。研究结果表明:1)六种豹子花属植物标本中都有雄花存在;根据雄性花和两性花的不同组合,形成雄性个体、两性花个体,和雄花两性花同株个体三种植株类型;2)个体大小(株高)和分布海拔之间不存在相关关系,和植株性别类型相关,即雄性个体一般显著小于具有雌性功能的两性花个体和雄花两性花同株个体;3)个体大小与花大小、每个个体开花总数和雌花数量成显著的正相关关系,而与每个个体的雄花数量无显著的相关关系。本研究更正了一直以来对豹子花属植物性系统的错误认识,首次报道雄花在豹子花属植物中普遍存在,并指出雄花和雄性个体的出现是大小依赖性分配的结果。同时,以研究实例证明了利用腊叶标本开展植物性系统多样性的可行性。     

利用腊叶标本初探豹子花属植物的性表达及其与个体大小的关系?

植物性系统进化过程中很少有植物通过雌性败育的方式实现性系统由联合走向分离,然而雄花在百合科植物中大量存在,引起了研究者的关注。本研究利用百合科豹子花属植物的腊叶标本,获取它们的花性别表型、花大小、株高以及分布海拔等信息探讨豹子花属植物的性表达样式,并对样本量较多的开瓣豹子花、云南豹子花、多斑豹子花和豹子花四个种的性表达及其与个体大小的关系进行分析。研究结果表明：1)六种豹子花属植物标本中都有雄花存在;根据雄性花和两性花的不同组合,形成雄性个体、两性花个体,和雄花两性花同株个体三种植株类型;2)个体大小(株高)和分布海拔之间不存在相关关系,和植株性别类型相关,即雄性个体一般显著小于具有雌性功能的两性花个体和雄花两性花同株个体;3)个体大小与花大小、每个个体开花总数和雌花数量成显著的正相关关系,而与每个个体的雄花数量无显著的相关关系。本研究更正了一直以来对豹子花属植物性系统的错误认识,首次报道雄花在豹子花属植物中普遍存在,并指出雄花和雄性个体的出现是大小依赖性分配的结果。同时,以研究实例证明了利用腊叶标本开展植物性系统多样性的可行性。     

Pattern of Flower and Fruit Production in Stryphnodendron adstringens, an Andromonoecious Legume Tree of Central Brazil

Abstract: Patterns of flower and fruit production in racemes of Stryphnodendron adstringens, an andromonoecious Brazilian savanna tree species, were studied in two natural areas near Uberlândia-MG. Racemes were divided in three parts: apex, centre, and base. Number of flowers, gender, and nectar and pollen production were analyzed for each section. Frequency of visitors to each part of the inflorescence was also quantified. Hand self- and cross-pollinations were performed in complete racemes and fruit set used to determine breeding system. The racemes produced a mean of 329 flowers, more densely packed in the central portion. Hermaphrodite and male flowers occur along the inflorescence but hermaphrodite flowers are more common in the centre. Fruit set was markedly low but does not seem to be limited by pollination service, since free open-pollinated racemes and hand cross-pollinated ones do not differ in fruit production rates. Fruits resulted mostly from cross-pollinated flowers and fruit production was biased to the central portion of the raceme. Nectar yield was higher in the central portion of the raceme and visitors arrived more commonly on this portion of the inflorescence. However, most flowers did not produce nectar. The pattern of fruit production seems to be a consequence of the hermaphrodite flower distribution in the raceme and it is not constrained by pollen flow or flower opening sequence.     

SEXUAL ALLOCATION AND ANDROMONOECY: RESOURCE INVESTMENT IN MALE AND HERMAPHRODITE FLOWERS OF SOLANUM CAROLINENSE (SOLANACEAE)

Male and hermaphrodite flowers from the andromonoecious perennial Solanum carolinense were compared. Hermaphrodite flowers were 11–16% heavier than males, and this difference was consistent for two clones studied. Hermaphrodite flowers contained a greater amount of nitrogen than did male flowers, but males had higher percent nitrogen. Male and hermaphrodite flowers had equal investment in male structures: stamen mass, number of pollen grains, mass of pollen grains ejected by vibration, and pollen size were all similar for the two flower types. In contrast, male flowers had reduced masses of disfunctional female structures: ovaries of males were ⅓ as massive, and styles 1/7; as massive, as those of hermaphrodites. These results are consistent with the hypothesis that male flowers (which occur where fruit set is unlikely) increase male fitness through pollen donation, while saving resources that would otherwise be invested in hermaphrodite flowers that abscise.     

Sex allocation and reproductive success in the andromonoecious perennial Solanum carolinense (Solanaceae). I. Female

Relative allocation of resources to growth vs. reproduction has long been known to be an important determinant of reproductive success. The importance of variation in allocation to different structures within reproductive allocation is somewhat less clear. This study was designed to elucidate the importance of allocation to vegetative vs. reproductive functions, and allocation within reproductive functions (sex allocation), to realized female success in an andromonoecious plant, Solanum carolinense. Allocation measurements were taken on plants in experimental arrays exposed to natural pollination conditions. These measurements included total flower number, the proportion of flowers that were male, flower size, and vegetative size. Flower number explained the majority of the variation among individuals in their success-that is, there was strong selection for increased flower production. There was also selection to decrease the proportion of flowers that were male, but neither flower size nor vegetative size (a measure of overall resource availability) were direct determinants of female success. After Bonferroni corrections for multiple comparisons, most phenotypic correlations among the traits measured were nonsignificant. Thus, in this andromonoecious species there is not a strong relationship between resource availability (vegetative size) and female success, and female success is instead determined by the relative production of the two different flower types.     

ANDROMONOECY IN ZIGADENUS PANICULATUS (LILIACEAE): SPATIAL AND TEMPORAL PATTERNS OF SEX ALLOCATION

I describe patterns of sex allocation and gamete packaging in the andromonoecious lily Zigadenus paniculatus. In this species, pistil length was continuously, but bimodally, distributed within plants, and smaller pistils contained fewer mature ovules. In hermaphrodite flowers, ovule number per flower increased with blooming rank in small plants but decreased with blooming rank in large plants. Flowers with pistils less than three-fourths stamen length almost never produced fruits and were classified as males. The pedicel, tepals, stamens, and pistil of hermaphrodite flowers were all heavier than those of males. Hermaphrodite flowers were concentrated on the terminal raceme, males on the lower racemes. In combination with acropetal blooming, this spatial separation of flower types resulted in a seasonal decline in the proportion of open flowers that were hermaphrodite. However, individual flowers were protandrous, so that the population sex ratio, initially strongly male-biased, declined as the season progressed. Hand pollinations showed that plants were self-incompatible. Inflorescence size was positively correlated with bulb size, and plants with large inflorescences had a higher proportion of male flowers. Nutrient supplementation had no effect on inflorescence size, but increased the proportion of hermaphrodite flowers. Nutrient-supplemented plants also began blooming earlier than controls. I discuss these patterns in relation to the adaptive significance of andromonoecious breeding systems.     

Fruit set increases with maleness in the andromonoecious Acacia caven

In long-lived plants, sexual expression can be highly variable in time and space. The extent to which sexual dimorphism of flowers is expressed in the same or in separate individuals, may have implications for the plants’ dependence on pollen vectors, the compatibility of the pollen received, and the potential for setting fruit. Here, we account for variability in sexual expression in the small tree Acacia caven, which produces hermaphrodite and male flowers on the same or in separate individuals. We focus on whether individual sexual expression influences fruit set, which latter has been reported to be extremely low in this species. Individual sexual expression, estimated as the hermaphrodite: male flowers ratio was variable both within and among plants across two reproductive seasons. Though male flower production could be very high (up to 99% of the flowers), all trees produced both flower types within the same individual, thus confirming andromonoecy in this species. More interestingly, hermaphrodite: male flowers ratio had a negative effect on fruit set. This pattern was consistent across two reproductive seasons and suggests that maleness should favor female function. Similar trends found in other plant species with the same sexual system support the hypothesis that male flowers of andromonoecious species may contribute to reduce self-pollen interference compared with hermaphrodite flowers. By favoring the deposition of compatible pollen grains and increasing fruit set, maleness would then help to maintain andromonoecy in this and other andromonoecious species.     

冠果草的性表达状态及其进化含义

通常认为雄花两性花同株是植物性表达两性花进化到雌雄异株的过渡类型之一。慈姑属仅冠果草（Ｓａｇｉｔｔａｒｉａ ｇｕｙａｎｅｎｓｉｓ Ｈ．Ｂ．Ｋ．ｓｕｂｓｐ．ｌａｐｐｕｌａ（Ｄ．Ｄｏｎ）Ｂｏｊｉｎ）的性表达为典型的雄花两性花同株,其他种为雌雄同株。对冠果草野外和实验居群的性配置进行了定量观察。东乡和武夷山居群雄花的比例分别为２．４８％０．９６％。实验表明,栽培条件影响冠果草的性表达：在营养较好的条件下     

Floral sex allocation and reproductive success within inflorescences of Hosta ventricosa,a pseudogamous apomict

Aims Within inflorescences of sexually reproducing hermaphrodites, the production of ovules, fruits and seeds commonly declines from basal (early-opening) to distal (late-opening) flowers, while pollen production remains constant or only changes slightly, with the result that distal (late-opening) flowers become functionally male. However, few empirical studies have specifically examined whether or not changes in allocation to pollen production actually lead to changes in the number of seeds sired, a more direct measure of male fitness. In pseudogamous apomicts, fitness depends on the number of seeds produced; thus, a contrasting pattern of variation in the pollen-to-ovule (P/O) ratio within inflorescences might be expected.Methods We investigated floral sex allocation and reproductive success within racemes of Hosta ventricosa, a pseudogamous apomictic hermaphrodite possessing flowers that open acropetally. We quantified variations in pollen number, ovule number, the P/O ratio and fruit and seed production, from 2007 to 2011, among flowers within racemes of four populations of H. ventricosa in southwest China. Ecological causes for fruit and seed production were evaluated by observing patterns of pollen deposition, flower removal and supplemental pollination.Important findings Pollen number, ovule number and the P/O ratio declined from basal-to-distal positions in all sampled populations (years). Fruit and seed production decreased distally in most populations (years). Low fruit and seed set of distal flowers was not due to pollen limitation because pollen deposition never declined distally and the low fruit and seed set of distal flowers remained even after supplementary pollination was provided. The flower-removal experiment indicated that inter-fruit competition for resources among flowers was common. The low P/O ratio of distal flowers in H. ventricosa might be favored because they were unable to obtain fitness by donating pollen and siring seeds on other plants. Our study may help to understand the adaptive significance of sex allocation among flowers within inflorescences of sexually reproducing hermaphrodites.     

Breeding systems in Coriaria (Coriariaceae)

Species of Coriaria are wind-pollinated and self-compatible. Discrepancies in the literature regarding sex expression in the genus may be attributed to inter- and intra-floral dichogamy. The southern hemisphere species and the Himalayan C. terminalis are evergreen phanerophytes or high elevation hemicryptophytes, which flower on new wood. Their racemes are many-flowered and are produced singly (terminal) or more usually in pairs in the axils at each node, and contain protogynous, hermaphrodite flowers. The northern hemisphere species are deciduous phanerophytes, which flower on old wood. Their racemes are few-flowered but aggregated in axillary clusters of up to 12 per node; sex expression is andromonoecious or monoecious (depending on species), with inter-floral protandry and intra-floral protogyny. In this lineage of species the evolution of a deciduous habit, the presentation of an initial male phase (inter-floral protandry), and the aggregation of many, few-flowered racemes at each node are interpreted as responses to selection pressures in the seasonal climate of a northern, mixed woodland environment.     

Reproductive ecology of Cneorum tricoccon L. (Gneoraceae) in the Balearic Islands

This paper examines some aspects of the reproductive biology of Cneorum tricoccon L. (Cneoraceae), a Mediterranean relict shrub which evolved under tropical conditions during the Tertiary. The breeding system, the flowering and fruiting phenology, and the variability in fecundity within and among populations of this plant were examined in the Balearic Islands. The plant is andromonoecious, and pollen from male flowers appeared to be more fertile than pollen from hermaphrodite flowers. There was no limitation of pollen, and xenogamous crosses produced more fruit than geitonogamous ones. The efficiency of male flowers suggests that their use increases plant fitness, thus maintaining such a breeding system. Flowering time is unusual compared with other species in the habitat; there is synchrony among individuals, and flowers are produced almost continuously from November through June. Floral sex ratio (number of hermaphrodite flowers: total number of flowers) varied greatly both through the flowering season and between years and was not consistent through time, suggesting that sex expression may be determined more by factors such as resource status of the plant than by genetic factors. Fully developed fruits are observed from December to July. Fecundity varied among individuals depending upon plant size and was consistent during the three years of the study (1992–1994). Fruit crop also differed strongly among sites. The greatest, most vigorous and thus most fecund plants are found in some populations of Mallorca island, especially at high altitudes. In other Balearic islands with low altitudes (<200 m), such as Cabrera, individuals are always short, less leafy and less fecund.