FLORAL DEVELOPMENT OF HYDROCHARIS MORSUS-RANAE (HYDROCHARITACEAE)

In both male and female flowers of H. morsus-ranae the primordia of the floral appendages appear in an acropetal succession consisting of alternating trimerous whorls. In the male flower a whorl of sepals is followed by a whorl of petals, three whorls of stamens, and a whorl of filamentous staminodes. The mature androecial arrangement therefore consists of two antisepalous stamen whorls, an antipetalous whorl of stamens, and antipetalous staminodes. Shortly before anthesis, basal meristematic upgrowth between filaments of adjacent whorls produces paired stamens, joining Whorls 1 and 3, and Whorl 2 with the staminodial whorl. A central domelike structure develops between the closely appressed filaments of the inner stamen and staminodial whorl, giving the structure a lobed appearance. After petal inception in the female flower a whorl of antisepalous staminodes develop, each of which may bifurcate to form a pair of staminodes. During staminode development a girdling primordium arises by upgrowth at the periphery of the floral apex. The girdling primordium rapidly forms six gynoecial primordia, which then go on to produce six free styles with bifid stigmas. Intercalary meristem activity, below the point of floral appendage attachment, leads to the production of a syncarpous inferior ovary with six parietal placentae. The styles and carpels remain open along their ventral sutures. During the final stages of female floral development, several hundred ovules develop along the carpel walls, and three nectaries develop dorsally and basally on the three antipetalous styles.     

HOMEOSIS IN THE FLOWERS OF THE ZINGIBERALES

Homeosis has played an important role in the evolution of the flowers of the Zingiberales, especially those of the Ginger Group. In the Zingiberaceae, two members of the outer androecial whorl are replaced by a lip, and two members of the inner androecial whorl are replaced by petaloid staminodes. Most of the androecium of the Costaceae has also been replaced by petaloid structures, and the single fertile stamen is often attached to an enlarged petaloid “filament.” The Cannaceae and Marantaceae have one-half of one fertile anther and three to four variously modified staminodes. In contrast, homeosis has played a minor role in floral evolution of the Banana Group. Only in the Heliconiaceae has a stamen been replaced by a staminode. In none of the families of the Zingiberales do the staminodes assume the total “form or character” of any perianth members. Because of this, it is reasonable to extend the definition of homeosis to include replacement by an organ like, but not identical to, some other part of the plant.     

The floral development of Popowia whitei (Annonaceae)

A study of the floral ontogeny of Popowia was carried out to investigate the phyllotactic arrangement of the floral organs and occurring trends in the androecium of Annonaceae. The flower buds arise on a common stalk in the axil of a bract. Three sepals emerge in quick succession and are rapidly overrun in size by two whorls of petals. The androecium is initiated centripetally in successive whorls. A first whorl of three pairs of outer staminodes emerges opposite the outer petals and is followed by nine staminodes. Next a whorl of nine fertile stamens arises in alternation with the second whorl of staminodes. The carpels arise in three alternating whorls of nine. The nature of the perianth parts is morphologically identical. The process of cyclisation of the androecium from a spiral is discussed for Annonaceae and Magnoliidae in general. The inception of the three outer stamen pairs is a widespread reductive step for multistaminate androecia in the process of oligomerization. It is proposed to define the cyclic inception of numerous stamens as whorled polyandry, being an intermediate step between true polyandry and a reduced stamen number in whorls. The absence of a cup-like shape in the carpel development is related to the flattened receptacle.     

Comparative structure and pollen production of the stamens and pollinator-deceptive staminodes of Commelina coelestis and C. dianthifolia (Commelinaceae)

BACKGROUND AND AIMS: Flowers of Commelina coelestis and C. dianthifolia provide pollen alone as a floral reward, and rely on visual cues to attract pollinators. Three stamen types, all producing pollen, occur in each of these species: two cryptically coloured lateral stamens, a single cryptically coloured central stamen and three bright yellow staminodes that sharply contrast with the blue to purple corolla. The objective was to compare the stamen structure and pollen characteristics of each of the three stamen types, and to test the hypothesis that the staminodes are poor contributors of viable pollen for the siring of seed. The pollination roles of the three stamen types and the breeding systems of both species were also explored. Methods: Light, fluorescence and scanning electron microscopy were utilized to examine stamen morphology and pollen structure and viability. Controlled hand pollinations were used to explore the breeding system of each species. Filament and style lengths were measured to investigate herkogamy and autogamy. KEY RESULTS: Pollen from all stamen morphs is viable, but staminode pollen has significantly lower viability. Pollen polymorphism exists both (a) between the lateral and central stamens and the staminodes, and (b) within each anther. Lateral and central stamens have thicker endothecia with a greater number of secondary cell wall thickenings than the staminodes. CONCLUSIONS: Both species are entomophilous and facultatively autogamous. Lateral stamen pollen is important for cross-pollination, central stamen pollen is utilized by both species as a pollinator reward and for delayed autogamy in C. dianthifolia, and the staminodes mimic, by means of both colour and epidermal features, large amounts of pollen to attract insects to the flowers. Pollen from all three anther morphs is capable of siring seed, although staminode pollen is inferior. The thin staminode endothecium with fewer secondary thickenings retards staminode dehiscence.     

Floral ontogeny of Annonaceae: evidence for high variability in floral form

Background and Aims

Annonaceae are one of the largest families of Magnoliales. This study investigates the comparative floral development of 15 species to understand the basis for evolutionary changes in the perianth, androecium and carpels and to provide additional characters for phylogenetic investigation.

Methods

Floral ontogeny of 15 species from 12 genera is examined and described using scanning electron microscopy.

Key Results

Initiation of the three perianth whorls is either helical or unidirectional. Merism is mostly trimerous, occasionally tetramerous and the members of the inner perianth whorl may be missing or are in double position. The androecium and the gynoecium were found to be variable in organ numbers (from highly polymerous to a fixed number, six in the androecium and one or two in the gynoecium). Initiation of the androecium starts invariably with three pairs of stamen primordia along the sides of the hexagonal floral apex. Although inner staminodes were not observed, they were reported in other genera and other families of Magnoliales, except Magnoliaceae and Myristicaceae. Initiation of further organs is centripetal. Androecia with relatively low stamen numbers have a whorled phyllotaxis throughout, while phyllotaxis becomes irregular with higher stamen numbers. The limits between stamens and carpels are unstable and carpels continue the sequence of stamens with a similar variability.

Conclusions

It was found that merism of flowers is often variable in some species with fluctuations between trimery and tetramery. Doubling of inner perianth parts is caused by (unequal) splitting of primordia, contrary to the androecium, and is independent of changes of merism. Derived features, such as a variable merism, absence of the inner perianth and inner staminodes, fixed numbers of stamen and carpels, and capitate or elongate styles are distributed in different clades and evolved independently. The evolution of the androecium is discussed in the context of basal angiosperms: paired outer stamens are the consequence of the transition between the larger perianth parts and much smaller stamens, and not the result of splitting. An increase in stamen number is correlated with their smaller size at initiation, while limits between stamens and carpels are unclear with easy transitions of one organ type into another in some genera, or the complete replacement of carpels by stamens in unisexual flowers.     

Pseudodiplostemony, and its implications for the evolution of the androecium in the Caryophyllaceae

The androecium of the Caryophyllaceae is varied, ranging from a two-whorled condition to a single stamen. A number of species belonging to the three subfamilies, Caryophyl-loideae, Alsinoideae and Paronychioideae have been studied ontogenetically with the SEM to understand their peculiar androecial development in the broader context of the Caryophyllales alliance. Although patterns of initiation are highly variable among species, there are three ontogenetic modes of stamen initiation: all stamens simultaneous within a whorl, the antepetalous stamens simultaneous and the antesepalous sequentially with a reversed direction, or both whorls sequentially with or without a reversed direction. The most common floral (ontogenetic) sequence of the Caryophyllaceae runs as follows: five sepals (in a 2/5 sequence), the stamens in front of the three inner sepals successively, stamens opposite the two outermost sepals, five antepetalous stamens (simultaneously or in a reversed spiral superimposed on the spiral of the antesepalous stamens), five outer sterile (petaloid) organs arising before, simultaneously or after the antesepalous stamens, often by the division of common primordia. A comparison with the floral configurations of the Phytolaccaceae and Molluginaceae indicates that the outer petaline whorl of the Caryophyllaceae corresponds positionally to the alternisepalous stamens of somePhytolacca, such asP. dodecandra. The difference withP. dodecandra lies in the fact that an extra inner or outer whorl is formed in the Caryophyl-laceae, in alternation with the sepals. A comparable arrangement exists in the Molluginaceae, though the initiation of stamens is centrifugal. A comparison of floral ontogenies and the presence of reduction series in the Caryophyllaceae support the idea that the pentamerous arrangement is derived from a trimerous prototype. Petals correspond to sterillized stamens and are comparable to two stamen pairs opposite the outer sepals and a single stamen alternating with the third and fifth sepals. Petals are often in a state of reduction; they may be confused with staminodes and they often arise from common stamenpetal primordia. The antesepalous stamen whorl represents an amalgamation of two whorls: initiation is reversed with the stamens opposite the fourth and fifth formed sepals arising before the other, while the stamens opposite the first and second formed sepals are frequently reduced or lost. Reductive trends are correlated with the mode of initiation of the androecium, as well as changes in the number of carpels, and affect the antesepalous and antepetalous whorls in different proportions. It is concluded that the androecium of the Caryophyllaceae is pseudodiplos-temonous and is not comparable to diplostemonous forms in the Dilleniidae and Rosidae. The basic floral formula of Caryophyllaceae is as follows: sepals 5—petals 5 (sterile stamens)—antesepalous stamens 3+2—antepetalous stamens 5 gynoecium 5.     

Study of homeosis in the flower of Philodendron (araceae): a qualitative and quantitative approach

This study deals specifically with floral organogenesis and the development of the inflorescence of Philodendron squamiferum and P. pedatum. Pistillate flowers are initiated on the lower portion of the inflorescence and staminate flowers are initiated on the distal portion. An intermediate zone consisting of sterile male flowers and atypical bisexual flowers with fused or free carpels and staminodes is also present. This zone is located between the sterile male and female floral zones. In general, the portion of bisexual flowers facing the male zone forms staminodes, and the portion facing the female zone develops an incomplete gynoecium with few carpels. The incomplete separation of some staminodes from the gynoecial portion of the whorl shows that they belong to the same whorl as the carpels. There are two levels of aberrant floral structures in Philodendron: The first one is represented by the presence of atypical bisexual flowers, which are intermediates between typical female flowers and typical sterile male flowers. The second one is the presence of intermediate structures between typical carpels and typical staminodes on a single atypical bisexual flower. The atypical bisexual flowers of P. squamiferum and P. pedatum are believed to be a case of homeosis where carpels have been replaced by sterile stamens on the same whorl. A quantitative analysis indicates that in both species, on average, one staminode replaces one carpel.     

Ontogenetic origins of floral bilateral symmetry in Moringaceae (Brassicales)

Floral morphology of the 13 species of Moringa ranges from actinomorphic flowers with little hypanthium to highly zygomorphic flowers with well-developed hypanthia. Scanning electron and light microscopy were used to identify ontogenetic differences among two actinomorphic and eight zygomorphic species. All species show traces of zygomorphy between petal organogenesis and anther differentiation. At late organogenesis, zygomorphy is manifest by one petal being larger than the others, slight unidirectional maturation of the anthers, and in many species, some staminodes may be missing. At organ differentiation and beyond, the actinomorphic species show a trend toward increasing actinomorphy, whereas the zygomorphic features of early ontogeny are progressively accentuated throughout the ontogeny of the zygomorphic species. Because of the early traces of zygomorphy throughout the family, ontogeny in Moringa does not resemble that known from the sister taxon Caricaceae, which has flowers that are actinomorphic throughout ontogeny. Great intraspecific variation was found in floral plan in the actinomorphic-flowered species in contrast to the zygomorphic species. Each of the main clades in the family is distinguished by at least one feature of floral ontogeny. In general, ontogenetic differences that are congruent with deeper phylogenetic splits tend to occur earlier in ontogeny than those congruent with more recent divergences.     

Floral ontogeny and vasculature in Xyridaceae,with particular reference to staminodes and stylar appendages

We provide a detailed comparative study of floral ontogeny and vasculature in Xyridaceae, including Xyris, Abolboda and Orectanthe. We evaluate these data in the context of a recent well-resolved phylogenetic analysis of Poales to compare floral structures within the xyrid clade (Xyridaceae and Eriocaulaceae). Xyrids are relatively diverse in both flower structure and anatomy; many species incorporate diverse and unusual floral structures such as staminodes and stylar appendages. Xyridaceae possess three generally epipetalous stamens in a single whorl; the “missing” stamen whorl is either entirely absent or transformed into staminodes. Fertile stamens each receive a single vascular bundle diverged from the median petal bundle. In Xyris, the stamen bundle diverges at the flower base, but it diverges at upper flower levels in both Abolboda and Orectanthe. In species of Abolboda that possess staminodes, staminode vasculature is closely associated with the lateral vasculature of each petal. Despite the likely sister-group relationship between Eriocaulaceae and Xyridaceae, our character optimization indicates that the stylar appendages that characterize some Xyridaceae (except Xyris and Achlyphila) are non-homologous with those of some Eriocaulaceae. On the other hand, it remains equivocal whether the loss of a fertile outer androecial whorl occurred more than once during the evolutionary history of the xyrid clade; this transition occurred either once followed by a reversal to fertile stamens in Eriocauloideae and staminodes in some Xyridaceae, or twice independently within both Xyridaceae and Eriocaulaceae.     

Floral development of dioecious species and trends of floral evolution in Piper sensu lato

The initiation of the floral parts (mainly stamens and carpels) is described for the four dioecious species of Piper: Piper polysyphorum C. DC, P. bavinum C. DC., P. pedicellatum C. DC., P. pubicatulum C. DC. The initiation order resembles that in the perfect flowers of some species, such as P. amalago. The carpels are initiated simultaneously, in most cases, as three primordia. In P. polysyphorum , carpel tips split into two lobes, so that finally a four- or five-lobed stigma will be formed when the ovary is fully developed. The staminodes (exactly, staminodial primordia) in the female flowers are initiated in the same order as the stamens in the male flowers and remain until the ovaries are enclosed. The unisexual flowers have stamens reduced to three or two. The reduction of stamen or staminode (staminodial primordium) number is accompanied by the change of their positions from opposite the carpels to alternate. After the initiation of the staminodes, or, exactly staminodial primordia, in the female flowers, the central part of the floral apex forms a ring meristem which is triangular. The carpel primordia (often three) are initiated on the three points of the ring meristem. The evolutionary trends of the flowers of Piper sensu lato are discussed.     

Floral ontogeny, pattern formation, and evolution in Hibbertia and Adrastaea (Dilleniaceae)

Floral development was compared with scanning electron microscopy in 12 Australian species of Hibbertia representing most of its morphological variation, and in the related Adrastaea (Dilleniaceae). Calyx and corolla arise in quincuncial helices in radially symmetrical species, while the petals initiate unidirectionally from one side in zygomorphic species. Stamen number (3-200+) proliferates by centrifugal addition of individual primordia or by innovations of common primordia and ring meristems. Common primordia arise in single-stamen positions alternately with petals, and each produces one to several stamens centrifugally that remain attached to a shared base and form a stamen fascicle. A ring meristem in Adrastaea initiates a whorl of five stamens, alternate with the first stamens but outside their whorl. In radially symmetrical species of Hibbertia, a first ring of stamens is supplemented centrifugally by additional stamens on a meristem ring. The first stamens in zygomorphic species of Hibbertia initiate as a terminal ridge on the floral apex, with subsequent stamens added centrifugally on one side and two carpels initiated on the opposite side. The carpels arise as a simultaneous ring in radially symmetrical flowers, or as a simultaneous pair in zygomorphic species. Staminodial presence is viewed as of minor significance. Four pollinator syndromes are proposed for Hibbertia, related to differing floral architecture.     

Reevaluation of the perianth and androecium in Caryophyllales: implications for flower evolution

The Caryophyllales have the highest diversity in androecial patterns among flowering plants with stamen numbers ranging from 1 up to 4,000. Thanks to the recent progress in reconstructing the phylogeny of core Caryophyllales, questions of floral evolution, such as the origin and diversification of the androecium, can be readdressed. Caryophyllales are unique among core eudicots in sharing an androecial ring meristem or platform with centrifugal development of stamens and petals. Stamens are basically arranged in two whorls and evolution within the clade depends on the shift of either the antesepalous or the alternisepalous whorls to an upper position on the ring meristem and the reduction of the other. Four main developmental phenomena are responsible for the high diversity in androecial patterns: (1) the sterilisation of the outermost stamens through a division of common primordia; (2) the secondary addition of stamens by a centrifugal initiation of supernumerary stamens superimposed on a lower stamen number; (3) the pairwise displacement of alternisepalous stamens to the middle of the outer sepals and their potential fusion, or as part of a pluristaminate androecium; (4) the inversed sequence, reduction and loss of antesepalous stamens. Shifts in stamen numbers depend on pressures of the calyx and carpels and changes in the number of the latter. These patterns are expressed differently in the three main evolutionary lines of core Caryophyllales and are systematically relevant: (1) A basal grade of Caryophyllales, culminating with Caryophyllaceae, Amaranthaceae, Stegnosperma and Limeum, has the antesepalous stamens initiated in upper position on the ring meristem, and alternisepalous stamens are preferentially reduced. Among the antesepalous whorl there is a progressive loss of stamens following a sequence inversed to sepal initiation. Petaloid staminodes are formed by the radial division of outer stamens. (2) The raphide-clade and Molluginaceae are characterized by alternisepalous stamens in upper position on the ring meristem, with a trend to secondary stamen multiplication, and loss of antesepalous stamens. (3) The Portulacineae share the pattern of the raphide clade, but some taxa show shifts to an upper position on the ring meristem of either antesepalous or alternisepalous stamens, linked with secondary multiplications and reduction of either whorl. Different floral characters are plotted on a recent cladogram of Caryophyllales. The data show a consistent correlation between shifting carpel and stamen numbers independent of perianth evolution. Comparative data suggest that the basic androecium of Caryophyllales consists of two whorls of five stamens, linked with an absence of petals, and the evolution of the androecium is a combination of reductions and secondary multiplications of stamens with a highly predictive systematic value.     

The Classification and Functional Significance of Staminodes in Angiosperms

All staminodes in an androecium fail to produce viable pollen grains and cannot contribute directly to male fitness. Staminodes are identified in the flowers of approximately 54% of known genera representing >32% of all angiosperm families. The functional morphology and biochemistry of staminodes differs significantly from stamens with fertile anthers. In the absence of sperm production, some staminodes evolved novel adaptations contributing to the reproductive success of their flowers. We subdivided these staminodes into eight functional types: 1) Staminodes offering visual/olfactory cues; 2) Staminodes offering edible/inedible rewards; 3) Staminodes that deceive pollinators with false rewards; 4) Staminodes facilitating or directing the movements of pollinators in flowers;5) Stami nodes that facilitate stigma movement; 6) Staminodes functioning as secondary pollen presenters; 7) Staminodes that protect other floral organs; 8) Staminodes that prevent mechanical self pollination (autogamy). As a component within a flower, the majority of staminodes function as promoters of reproductive success by interacting directly with the pollinator to increase pollination efficiency (both pollen dispersal and deposition). Therefore, it is not surprising that one staminode may have more than one function over the flower′s lifespan and is closely associated with the size, abundance, behavior and taxonomic diversity of pollinators, floral predators and thieves. To correctly evaluate the function of staminodes, multi disciplinary approach using a range of protocols, equipment and materials is suggested. This approach allows us to compare the roles different staminodes play in the reproductive success of both closely and distantly related angiosperms, then uncover their evolutionary significance in angiosperm diversification.     

Evolution of flower shape in <Emphasis Type="Italic">Plantago lanceolata</Emphasis>

Plantago lanceolata produces small actinomorphic (radially symmetric), wind-pollinated flowers that have evolved from a zygomorphic, biotically pollinated ancestral state. To understand the developmental mechanisms that might underlie this change in flower shape, and associated change in pollination syndrome, we analyzed the role of CYC-like genes in P. lanceolata. Related zygomorphic species have two CYC-like genes that are expressed asymmetrically in the dorsal region of young floral meristems and in developing flowers, where they affect the rate of development of dorsal petals and stamens. Plantago has a single CYC-like gene (PlCYC) that is not expressed in early floral meristems and there is no apparent asymmetry in the pattern of PlCYC expression during later flower development. Thus, the evolution of actinomorphy in Plantago correlates with loss of dorsal-specific CYC-like gene function. PlCYC is expressed in the inflorescence stem, in pedicels, and relatively late in stamen development, suggesting a novel role for PlCYC in compacting the inflorescence and retarding stamen elongation in this wind pollinated species.     

Vestigial organs as opportunities for functional innovation: the example of the Penstemon staminode

Vestigial organs arise commonly during morphological evolution, but they need not be destined for elimination. Instead, vestigial organs may facilitate functional innovation because their freedom from functional constraints allows them to assume novel roles that their functional progenitor could not perform. We illustrate this vestigial transition between functions with an experimental study of the staminode of Penstemon flowers. Previous phylogenetic and developmental studies indicate that this staminode represents a stamen that was lost phenotypically, but not genetically, and then reappeared in the tribe Cheloneae, to which Penstemon belongs. To assess whether the Penstemon staminode has adopted a novel function(s), we compared pollination of flowers with and without staminodes for two bee-pollinated species, P. ellipticus and P. palmeri, and two hummingbird-pollinated species, P. centranthifolius and P. rostriflorus. The staminode acts differently in the two bee-pollinated species. For P. ellipticus, which represents the basal Penstemon lineage, the staminode hinders pollinator access to nectar, which increases visit duration and pollinator contact with sexual organs, thereby increasing pollen receipt by stigmas and controlling pollen removal from anthers. In contrast, in P. palmeri, the staminode acts as a lever that enhances stigma contact with the pollinator, so that staminode removal reduced pollen receipt, but did not affect pollinator attraction, visit duration, or pollen removal. Unlike in bee-pollinated species. staminode removal from hummingbird-pollinated species did not affect any measured aspect of pollination, indicating that the staminode serves no function in this derived pollination system. These results illustrate several features of vestigial organs: loss of function can be temporary; loss of function facilitates the evolution of novel roles; and functional reinvention will often involve only a single role, thus increasing the chance of both secondary loss of function (bird-pollinated penstemons) and functional switches (P. palmeri).     

大戟科麻疯树属三种植物花器官发生

利用扫描电子显微镜观察了大戟科Euphorbiaceae麻疯树属Jatropha麻疯树J. curcas L.、佛肚树J. podagrica Hook.和棉叶麻疯树J. gossypifolia L.花器官发生。结果表明: 麻疯树、佛肚树和棉叶麻疯树花萼原基均为2/5型螺旋发生。在同一个种不同的花蕾中, 花萼的发生有两种顺序: 逆时针方向和顺时针方向。远轴面非正中位的1枚先发生。5枚花瓣原基几乎同时发生。雄花中雄蕊两轮, 外轮对瓣, 内轮对萼。研究的3种麻疯树属植物雄蕊发生方式有两种类型: 麻疯树亚属麻疯树的5枚外轮雄蕊先同时发生, 5枚内轮雄蕊后同时发生, 佛肚树亚属佛肚树和棉叶麻疯树雄蕊8-9枚, 排成两轮, 内外轮雄蕊同时发生。雌花的3枚心皮原基为同时发生。麻疯树属单性花, 雌花的子房膨大而雄蕊退化, 雄花的雄蕊正常发育, 子房缺失。根据雄蕊发生方式, 支持将麻疯树属分为麻疯树亚属subgen. Jatropha和佛肚树亚属subgen. Curcas。     

Additional notes on the floral biology of neotropical Lecythidaceae

Observations on the floral biology of seven species of New World Lecythidaceae, including the first report of bat pollination for neotropical members of the family, are presented. The shift from actinomorphic flowers with many stamens to zygomorphic flowers with fewer stamens and the concomitant change from pollen to nectar as the pollinator reward are discussed and related to the respective pollinators. Several mechanisms which operate to reduce competition for pollinators between sympatric species of the family are suggested.     

Floral development and phyllotactic variation in Ceratophyllum demersum (Ceratophyllaceae)

The floral development of staminate and pistillate flowers of Ceratophyllum demersum was observed, with particular focus on the phyllotactic variation in staminate flowers, using scanning electronic microscopy (SEM). We discerned patterns of development of some important new morphological features, e.g., the difference and discontinuity between the organ initiation in stamens and that in bracts (or tepals) and the initial presence of a mucilaginous appendage on each pistil. Female flowers are considered to be very specialized through reduction. In male flowers stamen initiation changes between early and late floral development. The four or five stamens in the outermost whorl initiate first on the abaxial and lateral sides of the floral apex and only later on the adaxial side (unidirectional). Later the inner stamens initiate spirally, and this is the main pattern in the stamen initiation. Members of each whorl differ among themselves in time of initiation and in ultimate size. The phyllotactic variation in staminate flowers of Ceratophyllum, suggested by previous studies, is derived from the variation in stamen number and the difference of stamen initiation between the early and later stages. The development in Ceratophyllum has some similarities to those of ANITA plants except for Nymphaeales.     

Notes on the Evolution of Androecial Organisation in the Magnoliophytina (Angiosperms)

This paper aims to summarize briefly and to update our ideas about androecial architecture formulated in earlier publications. Ontogenetic evidence of stamen development, viz. the initiation, arrangement and relationship of stamens to other floral morphomes, can be translated into a semophyletic scheme reflecting the phylogeny of the androecium. The ancestral androecium is discussed in the light of recent theoriesabout angiosperm phylogeny. Two divergent androecial processes are proposed for the angiosperms starting from a spiral androecium with a moderate number of stamens. However, transitions exist between spiral polyandry, numerous stamens in whorls, and chaotic polyandry. From an androecium with several alternating whorls of paired and single stamens, outer stamen pairs are retained following the successive loss of inner stamen whorls. Single stamens instead of pairs occur at the very end of this line and represent a more advanced condition. This line is mostly present in tri- and dimerous flowers. From the same starting point diplostemony (with two alternating whorls of single stamens) originated, again giving rise to various states usually present in pentamerous or tetramerous flowers.     

Flower development and anatomy of Clusia valerioi,a Central American species of Clusiaceae offering floral resin

The present paper is part of a study dealing with various aspects of reproduction of two Costa Rican Clusia species offering resin as a floral reward. It provides data on the floral development and flower (especially stamen and staminode) anatomy of one of the species, Clusia valerioi. In the early stages, both male and female flowers develop in the same manner. The bracts are distinguished by a decussate arrangement from the five sepals and five petals, which emerge in a spiral manner. In the male flowers the apical meristem forms five meristematic mounds (common stamen primordia) that are pentagonally arranged around the apical meristem in epipetalous position. From these mounds, the primordia of the proper stamina emerge in 3–5 whorls. Direction is centrifugal. In the centre, five hemispherical bulges arise which develop into carpel primordia. These, however, cease growth, stay rudimentary and are hidden by the stamens in the mature male flower. The adult stamens consist mainly of a thick angular filament column, while the two anthers situated at the flattened top are very small. One anther is annular and surrounds a second, hemispherical one right in the centre. At the periphery, these two pollen sacs (provided with a distinct wall of customary anatomy) are surrounded by a ring-like protuberance of the filament. The resin canals are situated at the periphery of the filament. Their schizogenous development is documented in cross sections. At anthesis, the resin is released from the ring-like filament protuberance by burst of the single-layered epidermis. In the female flower, the five meristematic mounds produce two whorls of staminode primordia. The development of the staminodes does not essentially differ from that of the fertile stamens, but some staminodes lack the central pollen sac and the other tissues do not develop into pollen grains. An attempt is made to derive the peculiar stamen morphology of Clusia valerioi and similar species from conventional stamens. Three hypotheses are proposed and discussed.