花叶芋(天南星科)的花器官发生

利用扫描电镜首次观察了天南星科花叶芋(Colocasia bicolor) 的花器官发生过程。花叶芋的肉穗花序由无花被的单性花构成, 雌花发生于花序基部, 雄花发生于花序上部, 中性花位于花序中间部位。雄花: 3 或4 个初生雄蕊原基轮状发生, 随后每个初生原基一分为二, 形成6或8个次生原基; 一部分次生原基在其后的发育过程中融合, 形成5 或7 枚雄蕊; 雄花发育过程中未见雌性结构的分化; 花药的分化先于花丝; 雄蕊合生成雄蕊柱。雌花: 合生心皮, 3或4个心皮原基轮状发生, 未见雄性结构的分化。中性花来源于雌雄花序过渡带上, 属于雄蕊原基的滞后发育以及发育成熟过程中的退化; 与彩叶芋属(Caladium)不同, 此过渡区未见畸形两性花。初生雄蕊原基二裂产生次生原基的次生现象在目前天南星科花器官发生中显得比较特殊, 同时初步探讨了次生原基的融合方式。     

掌叶木的花器官发生及其系统学意义

利用扫描电子显微镜和光学显微镜观察了掌叶木的花器官发生过程。观察结果表明: 花序原基最先发生, 然后形成两个大小不一的花原基; 萼片原基的发生不同步, 螺旋状向心发生; 4-5枚花瓣原基以接近轮状方式近同时发生; 不存在花瓣-雄蕊复合原基; 7-8枚雄蕊原基为近同时发生, 其生长较花瓣原基快; 心皮原基最后发生, 3枚心皮原基为同时发生。花为单性花。在雌花中, 子房膨大而雄蕊退化。在雄花中, 雄蕊正常发育, 子房退化。讨论了掌叶木花器官发生和发育的系统学意义。     

眼子菜的花器官发生

运用扫描电镜观察了眼子菜的花器官发生过程。结果表明：花原基从花序轴的基部开始以三数 交互轮状的方式发生,在花原基发生的早期具有明显的苞片原基形成。花器官是以向心的方式发生的, 二枚侧方花被片原基首先形成,紧接着产生二枚中间花被片。四枚雄蕊分两轮分别在与侧方花被和中 间花被相对的位置发生,四枚雄蕊原基在发生时均呈长条形。上述四轮花被和雄蕊虽然在时间上以二 数轮状的方式发生,但在空间上花被片和雄蕊各自分别排成一轮。最后,二个心皮原基在花原基顶端略 偏于一侧并与雄蕊相间的位置同时发生。有些花的二枚心皮原基发生后其中一枚很早即停止生长或仅 有一枚心皮原基形成。本文结果支持了眼子菜属心皮数目逐渐向简化的方向演化的观点。在花原基早期发育的过程中苞片原基的存在表明眼子菜属植物成熟花中缺乏苞片是简化的结果。     

千金榆花序及花器官发育

在扫描电镜下首次观察了桦木科鹅耳枥属千金榆花序和花的形态发生过程。千金榆雌花序由多个小聚伞花序螺旋状排列组成;每个小花序原基分化出1枚初级苞片和一团小花序原基分生组织,由小花序原基分生组织分化形成2个花原基和2个次级苞片;每个花原基分化出2个心皮原基,形成1个二心皮雌蕊;次级苞片远轴面发育快于近轴面,呈不均等的联合状;雌蕊基部有1层环状花被原基。雄花序为柔荑状,由多个小聚伞花序螺旋状排列组成;每个小花序原基分化出1枚初级苞片和一团小花序原基分生组织,由小花序原基分生组织分化出3个花原基分区,并分化形成3朵小花,小花无花被,位于两侧的小花分别有2枚雄蕊,位于中央的小花有4枚雄蕊,雄蕊共8枚,稀为10枚,该3朵小花为二歧聚伞状排列,其花基数应为2基数。     

榛属 (桦木科) 花序及花的形态发生

在扫描电镜下观察了桦木科榛属榛、毛榛和滇榛的花序和花的形态发生过程。榛属雌花序由多个小聚伞花序螺旋状排列组成;每个小花序原基分化出1枚初级苞片和一团小花序原基分生组织,由小花序原基分生组织分化形成2个花原基;每个花原基分化出2个心皮原基,形成二心皮雌蕊;雌蕊基部有2层花被原基,内层花被原基环状,外层花被发生于花原基近轴面和远轴面,近轴面和远轴面的花被不均等分化,外层花被发生早于内层花被。雄花序为柔荑状,由多个小聚伞花序螺旋状排列组成。每个小花序原基分化出1枚初级苞片和一团小花序原基分生组织,由小花序原基分生组织分化出2枚次级苞片和4~6个雄蕊原基,形成4~6枚雄蕊,每个雄蕊具4个药囊,在雄蕊原基分化形成4药囊雄蕊过程中,出现雄蕊原基纵裂,并且花丝纵裂至基部。为进一步全面探讨桦木科属间系统演化关系提供了证据。     

榛属（桦木科）花序及花的形态发生

在扫描电镜下观察了桦木科榛属榛、毛榛和滇榛的花序和花的形态发生过程。榛属雌花序由多个小聚伞花序螺旋状排列组成;每个小花序原基分化出1枚初级苞片和一团小花序原基分生组织,由小花序原基分生组织分化形成2个花原基;每个花原基分化出2个心皮原基,形成二心皮雌蕊;雌蕊基部有2层花被原基,内层花被原基环状,外层花被发生于花原基近轴面和远轴面,近轴面和远轴面的花被不均等分化,外层花被发生早于内层花被。雄花序为柔荑状,由多个小聚伞花序螺旋状排列组成。每个小花序原基分化出1枚初级苞片和一团小花序原基分生组织,由小花序原基分生组织分化出2枚次级苞片和4。6个雄蕊原基,形成4—6枚雄蕊,每个雄蕊具4个药囊,在雄蕊原基分化形成4药囊雄蕊过程中．出现雄蕊原基纵裂。并且花丝纵裂至基部。为进一步全面探讨桦木科属间系统演化关系提供了证据。     

丝瓜雄花和雌花发育特点的研究

丝瓜为单性花,雌雄同株植物。雄花发育过程中,不出现雌蕊原基,即无“两性期”。雄花发育早期,分化出五个雄蕊原基,以后发育成五个分离的雄蕊。雌花发育早期,有雄蕊原基的形成,即具“两性期”。以后随着雌花的发育,雄蕊逐渐退化。雌蕊具三心皮下位子房,发育早期,子房基部的胎座呈中轴胎座状,向上逐渐过渡转化形成侧膜胎座。     

铁木属(桦木科)花序及花的形态发生

在扫描电镜下观察了桦木科(Betulaceae)铁木属花序和花的形态发生过程。结果显示, 铁木雌花序由多个小聚伞花序螺旋状排列组成。每个小花序原基分化出1枚初级苞片和一团小花序原基分生组织, 由小花序原基分生组织分化形成1对次级苞片和2个花原基, 每个花原基分化出2个或3个心皮原基, 形成二心皮或三心皮雌蕊, 雌蕊基部有1层环状花被原基。雄花序为柔荑状, 由多个小聚伞花序螺旋状排列组成。每个小花序原基分化出1枚初级苞片和一团小花序原基分生组织, 由小花序原基分生组织分化出3个花原基分区, 位于中央的花原基分区, 分化形成5-6枚雄蕊原基, 两侧的花原基分区, 分别分化形成3-4枚雄蕊原基, 雄蕊原基分化形成四药囊雄蕊。雄蕊原基纵裂, 但花丝纵裂没有达到基部。     

臭椿花器官分化的初步研究

利用扫描电镜(SEM)和光镜(LM)对臭椿花序及花器官的分化和发育进行了初步研究,表明:1)臭椿花器官分化于当年的4月初,为圆锥花序;2)分化顺序为花萼原基、花冠原基、雄蕊原基和雌蕊原基。5个萼片原基的发生不同步,并且呈螺旋状发生;5个花瓣原基几乎同步发生且其生长要比雄蕊原基缓慢;雄蕊10枚,两轮排列,每轮5个原基的分化基本是同步的;雌蕊5,其分化速度较快;3)在两性花植株中,5个心皮顶端粘合形成柱头和花柱,而在雄株中,5个心皮退化,只有雄蕊原基分化出花药和花丝。本研究着重观察了臭椿中雄花及两性花发育的过程中两性花向单性花的转变。结果表明,臭椿两性花及单性花的形成在花器官的各原基上是一致的(尽管时间上有差异),雌雄蕊原基同时出现在每一个花器官分化过程中,但是,可育性结构部分的形成取决于其原基是否分化成所应有的结构:雄蕊原基分化形成花药与花丝,雌蕊原基分化形成花柱、柱头和子房。臭椿单性花的形成是由于两性花中雌蕊原基的退化所造成,其机理有待于进一步研究。     

我国山毛榉科植物中一个新分布的属——三棱栎属

乔木。三叶轮生具成对合生的叶柄间托叶,或叶互生具离生的托叶。花序穗状,自正常和退化两者叶的腋中生出,单性,雄花序位于下方而雌花序位于上方,或仅有雄花序,簇状,或为雌雄同序下方具雄花而上方具雌花。雄花序挺直或曲折。雄花:(1—)3—7朵簇生,每簇具1基生和2侧生苞片;花被具6个复瓦状裂片,裂片下部合生;雄蕊6,与花被裂片对生,花药大(如栎属Quercus),宽卵圆形,基部心形,近背着但不为丁字着;退化雄蕊缺失。雌花:单生或3(—7)朵簇生,两种情况下承以3枚     

Unisexual flower, spikelet, and inflorescence development in monoecious/dioecious Bouteloua dimorpha (Poaceae, Chloridoideae)

Unisexual flowers have evolved repeatedly in the angiosperms. In Poaceae, multiple transitions from bisexual to unisexual flowers are hypothesized. There appear to be at least three distinct developmental mechanisms for unisexual flower formation as found in members of three subfamilies (Ehrhartoideae, Panicoideae, Pharoideae). In this study, unisexual flower development is described for the first time in subfamily Chloridoideae, as exemplified by Bouteloua dimorpha. Scanning electron microscopy (SEM) and anatomy were used to characterize the development of male (staminate) and female (pistillate) flowers, spikelets, and inflorescences. We found the developmental pathway for staminate flowers in B. dimorpha to be distinct from that described in the other three subfamilies, showing gynoecial arrest occurs at a different stage with possible loss of some cellular contents. However, pistillate flowers of B. dimorpha had some similarity to those described in other unisexual-flowered grasses, with filament and anther differentiation in abortive stamens. Comparing our findings with previous reports, unisexual flowers seem to have evolved independently in the four examined grass subfamilies. This analysis suggests the action of different genetic mechanisms, which are consistent with previous observations that floral unisexuality is a homoplasious condition in angiosperms.     

Anatomy and ontogeny of unisexual flowers in dioecious Woonyoungia septentrionalis （Dandy） Law （Magnoliaceae）

Woonyoungia septentrionalis （Dandy） Law is aceae. The floral morphology and structure of the species a dioecious species with unisexual flowers in Magnoliare conspicuously different from other species and are important to the study of floral phylogeny in this family. The floral anatomy and ontogeny were investigated to evaluate the systematic position of W. septentrionalis, using scanning electron microscopy and light microscopy. All of the floral organs are initiated acropetally and spirally. The carpels are of conduplicated type without the differentiation of stigma and style. The degenerated stamens in the female flowers have the same structures as the normal stamens at the earlier developmental stages, but they do not undergo successive development and eventually degenerate. The male floral apex was observed to have the remnants of carpels in a few investigated samples. As the bisexual flower features could be traced both in the male and female flowers in W. septentrionalis, it suggests that the flower sex in Magnoliaceae tends toward unisexual. As well as the unisexual flowers, the reduced tepals and carpels and concrescence of carpels conform to the specialized tendency in Magnoliaceae, which confirms the derived position of W. septentrionalis in this family. As the initiation pattern of floral parts of W. septentrionalis is very similar to other species in this family, it needs further investigation and especially comparison with species in Kmeria to evaluate the separation of Woonyoungia.     

Flower biology of the cactus Coryphantha elephantidens in the tropical dry forest of Central Mexico

Floral traits and sexual systems in angiosperms are strategies that enhance outcrossing within hermaphrodite flowers and among individuals in a population. Sexual systems with unisexual flowers have also evolved among angiosperms, resulting in sex specialization. Furthermore, the interaction of floral traits and floral visitors determines successful plant reproduction. Globose cacti are bee pollinated, and variation in the diversity of their pollinator assemblages is strongly associated with floral phenotype. Our objective was to describe the floral biology of the cactus Coryphantha elephantidens and to determine its relationship with pollinators. Floral traits were studied by direct observations in live and fixed flowers. The breeding system was determined using two estimators based on floral morphology: pollen grains to ovules per flower (P/O) ratio and outcrossing index. Pollination treatments were conducted to determine the mating system. Floral visitors were recorded using direct observation. Flowers of C. elephantidens are variable in color, protandric, herkogamous and nectarless. Estimators of the breeding system indicated xenogamy, which is consistent with the obligate outcrossing revealed by the pollination experiment. Thirty-seven percent of the plants have female flowers that do not produce pollen, making this population functionally gynodioecious. Both fruit and seed set were high compared to other globose cacti. Pollinators included eight species of native bees, a more diverse pollinator assemblage than other globose cacti. Given the high pressure on pollen due to functional gynodioecy, nectarless flowers, an outcrossing mating system, and the necessity of pollinators to set seeds, we concluded that native bees are highly efficient pollinators that play a crucial role in the sexual reproduction of C. elephantidens.     

Architectural effects mimic floral sexual dimorphism in Solanum (Solanaceae)

Factors underlying apparent floral sexual dimorphism were examined in six species of andromonoecious Solanum section Lasiocarpa (Solanaceae). Both multivariate and univariate analyses show that hermaphroditic flowers are significantly larger than staminate flowers for all features measured. Thus, flowers could be characterized as sexually size dimorphic. However, when size variation due to flower position (architecture) is controlled experimentally, differences between the floral genders for the nongynoecial characters disappear; there is no difference in corolla or androecium size. Staminate flowers appear to be generally smaller than hermaphroditic flowers, not because of any difference related to primary sexual function, but because they tend to occur in the distal regions of each inflorescence. In contrast, significant differences between hermaphroditic and staminate flowers for primary female traits (ovary, style, and stigma) remain after controlling for position: the two floral types are truly dimorphic for these characters. We show that consideration of architectural effects can direct and refine hypotheses concerning the evolution of andromonoecy. More generally, if architectural effects on flower size are common among taxa with unisexual flowers, then these effects may contribute to the common perception of size dimorphism in taxa with unisexual flowers.     

Functional Monoecy Due to Delayed Anther Dehiscence: A Novel Mechanism in Pseuduvaria mulgraveana (Annonaceae)

Unlike most genera in the early-divergent angiosperm family Annonaceae, Pseuduvaria exhibits a diversity of floral sex expression. Most species are structurally andromonoecious (or possibly androdioecious), although the hermaphroditic flowers have been inferred to be functionally pistillate, with sterile staminodes. Pseuduvaria presents an ideal model for investigating the evolution of floral sex in early-divergent angiosperms, although detailed empirical studies are currently lacking. The phenology and pollination ecology of the Australian endemic species Pseuduvaria mulgraveana are studied in detail, including evaluations of floral scent chemistry, pollen viability, and floral visitors. Results showed that the flowers are pollinated by small diurnal nitidulid beetles and are protogynous. Pollen from both hermaphroditic and staminate flowers are shown to be equally viable. The structurally hermaphroditic flowers are nevertheless functionally pistillate as anther dehiscence is delayed until after petal abscission and hence after the departure of pollinators. This mechanism to achieve functional unisexuality of flowers has not previously been reported in angiosperms. It is known that protogyny is widespread amongst early-divergent angiosperms, including the Annonaceae, and is effective in preventing autogamy. Delayed anther dehiscence represents a further elaboration of this, and is effective in preventing geitonogamy since very few sexually mature flowers occur simultaneously in an individual. We highlight the necessity for field-based empirical interpretations of functional floral sex expression prior to evaluations of evolutionary processes.     

Floral development and vasculature in Eriocaulon (Eriocaulaceae) provide insights into the evolution of Poales

Background and AimsFloral developmental studies are crucial for understanding the evolution of floral structures and sexual systems in angiosperms. Within the monocot order Poales, both subfamilies of Eriocaulaceae have unisexual flowers bearing unusual nectaries. Few previous studies have investigated floral development in subfamily Eriocauloideae, which includes the large, diverse and widespread genus Eriocaulon. To understand floral variation and the evolution of the androecium, gynoecium and floral nectaries of Eriocaulaceae, we analysed floral development and vasculature in Eriocaulon and compared it with that of subfamily Paepalanthoideae and the related family Xyridaceae in a phylogenetic context.MethodsThirteen species of Eriocaulon were studied. Developmental analysis was carried out using scanning electron microscopy, and vasculature analysis was carried out using light microscopy. Fresh material was also analysed using scanning electron microscopy with a cryo function. Character evolution was reconstructed over well-resolved phylogenies.Key ResultsPerianth reductions can occur due to delayed development that can also result in loss of the vascular bundles of the median sepals. Nectariferous petal glands cease development and remain vestigial in some species. In staminate flowers, the inner stamens can emerge before the outer ones, and carpels are transformed into nectariferous carpellodes. In pistillate flowers, stamens are reduced to staminodes and the gynoecium has dorsal stigmas.ConclusionsFloral morphology is highly diverse in Eriocaulon, as a result of fusion, reduction or loss of perianth parts. The nectariferous carpellodes of staminate flowers originated first in the ancestor of Eriocaulaceae; petal glands and nectariferous branches of pistillate flowers originated independently in Eriocaulaceae through transfer of function. We present a hypothesis of floral evolution for the family, illustrating a shift from bisexuality to unisexuality and the evolution of nectaries in a complex monocot family, which can contribute to future studies on reproductive biology and floral evolution in other groups.     

Unisexual flowers as a robust synapomorphy in Cariceae (Cyperaceae)? Evidence for bisexual flowers in Schoenoxiphium

Cariceae, the largest tribe within Cyperaceae, comprises about 2000 species in five genera. Cariceae is usually considered to be distinct from other Cyperaceae by the presence of exclusively unisexual flowers and by the arrangement of the pistillate flowers in single-flowered spikelets that are enclosed by the flask-like spikelet prophyll (utricle or perigynium). The nature of several morphological features of the Cariceae inflorescence remains controversial. The staminate reproductive units, as well as earlier reported bisexual reproductive units in Schoenoxiphium have been considered to be reduced partial inflorescences, or flowers. Aims of this study are to test both interpretations, based on a floral ontogenetic investigation. Moreover, for the first time, detailed SEM micrographs are presented of the inflorescence and floral development and of bisexual flowers in Schoenoxiphium. We propose that ‘inhibition of bisexuality’ is a more robust synapomorphy in Cariceae than ‘presence of only unisexual flowers’.     

开花式样对传粉者行为及花粉散布的影响

理解植物花的特征可以从单花特征和群体特征两个层次入手。开花式样是植物的花在群体上的特征体现, 通过在开花数目、开花类型以及花的排列上的变化, 不同的开花式样对传粉者具有不同的吸引力, 影响昆虫在植株上的活动, 使花粉运动的方向发生相应变化, 从而影响着植物最终的交配结果。此外开花式样随环境改变也会发生一些变化。本文介绍了开花式样研究的进展, 对开花数目、开花类型以及花的排列等3个方面的已有研究进行了分别阐述, 并提出开花式样研究应更多地考虑影响传粉的各种因素。     

Characterization of unisexual flower development in the endangered mahogany tree Swietenia macrophylla King. (Meliaceae)

The selection of candidate plus trees of desirable phenotypes from tropical forest trees and the rapid devastation of the natural environments in which these trees are found have created the need for a more detailed knowledge of the floral and reproductive biology of tropical tree species. In this article, the organogenic processes related to unisexual flower development in tropical mahogany, Swietenia macrophylla , are described. Mahogany inflorescences at different developmental stages were evaluated using scanning electron microscopy or optical microscopy of histological sections. The unisexual flowers of S. macrophylla are usually formed in a thyrse, in which the positions of the female and male flowers are not random. Differences between male and female flowers arise late during development. Both female and male flowers can only be structurally distinguished after stage 9, where ovule primordia development is arrested in male flowers and microspore development is aborted in female flower anthers. After this stage, male and female flowers can be distinguished by the naked eye as a result of differences in the dimensions of the gynoecium. The floral characteristics of S. macrophylla (distribution of male and female flowers within the inflorescence, and the relative number of male to female flowers) have practical implications for conservation strategies of this endangered species.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 529–535.     

Phylogenetic insights into the correlates of dioecy in meadow-rues (Thalictrum, Ranunculaceae)

Numerous studies have examined the evolution of sexual systems in angiosperms, but few explore the interaction between these and the evolution of pollination mode. Wind pollination is often associated with unisexual flowers, but which evolved first and played a causative role in the evolution of the other is unclear. Thalictrum, meadow-rues (Ranunculaceae), provides a unique opportunity to study the evolution of these traits because it contains insect and wind pollination and four sexual systems. We used a phylogenetic approach to reconstruct ancestral states for sexual system, pollination mode, and geographic distribution in Thalictrum, and tested for correlations to uncover the factors involved in the evolution of unisexuality and wind pollination. Our results show that dioecy, andro- and gynomonoecy evolved at least twice from hermaphroditism. Wind pollination, unisexual flowers, and New World distribution were all significantly correlated. Wind pollination may have evolved early in the genus, followed by multiple losses and gains, and likely preceded the origin of unisexual flowers in several cases; we found no evidence for unisexual flowers evolving prior to wind pollination. Given a broad scale study showing the evolution of dioecy before wind pollination, our results from a finer scale analysis highlight that different evolutionary pathways are likely to occur throughout angiosperms.