Floral anatomy and systematics of Bretschneidera (Bretschneideraceae)

External morphology and anatomy of the flower and pollen of Bretschneidera sinensis Hemsl. are described to clarify the position of the family Bretschneideraceae relative to the Sapindales and the glucosinolate-producing families. Anatomical and micromorphological characters are investigated and sections are used to understand the structure of the flower. Observation of buds and sections reveal that the flower is obliquely monosymmetric, with the symmetry line running from one petal to a sepal. The upper petal shields the stamens and pistil and becomes positioned apically by the partial resupination of the pedicel. The octomerous androecium is characterized by variable empty positions which are related to the variable insertion of the three carpels. The loss of stamens is linked with a displacement of the remaining stamens. Floral anatomy demonstrates the presence of a nectary extending on the hypanthium from the base of the filaments to the base of the gynoecium. Details of floral anatomy are compared with members of Sapindaceae, Hippocastanaceae, Moringaceae, Akaniaceae, Tropaeolaceae and Capparaceae. Comparison with other characters supports a close relationship with Akaniaceae and Tropaeolaceae in an order Tropaeolales, in concordance with macromolecular results, either at the base of the glucosinolate clade, or in remote connection with the Sapindales. A number of floral anatomical characters with a strong phylogenetic signal are highlighted. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 139 , 29–45.     

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 floral development and floral anatomy ofChrysosplenium alternifolium, an unusal member of the Saxifragaceae

The floral development and anatomy ofChrysosplenium alternifolium were studied with the scanning electron microscope and light microscope to understand the initiation sequence of the floral organs and the morphology of the flower, and to find suitable floral characters to interpret the systematic position of the genus within the Saxifragaceae. The tetramerous flower shows a highly variable initiation sequence. The median sepals and first stamens arise in a paired sequence resembling a dimerous arrangement, but the first sepal and stamen arise on the side opposite to the bract. Transversal sepals and stamens emerge sequentially, as one side often precedes the other; sepals and stamens occasionally arise on common primordia. Initiation of the gynoecium is more constant with two median carpel primordia arising on a sunken floral apex. Several flowers were found to be pentamerous with a 2/5 initiation sequence. Flowers were invariably found to be apetalous without traces of petals in primordial stages; this condition is interpreted as an apomorphy. It is postulated that the development of a broad gynoecial nectary is responsible for the occurrence of an obdiplostemonous androecium. The gynoecium shows a number of anatomical particularities not observed in other Saxifragaceae. The presence and distribution of colleters is discussed.     

Floral ontogeny and anatomy inKoelreuteria with special emphasis on monosymmetry and septal cavities

The floral ontogeny and anatomy ofKoelreuteria paniculata have been investigated to understand the developmental basis for the occurring monosymmetry and the origin of the septal cavities. Petals arise sequentially and one petal is missing between sepals 3 and 5, or rarely between sepals 2 and 5. The eight stamens arise sequentially before petal initiation is completed. The last formed petal and one stamen arise on a common primordium. Two stamen positions are empty (opposite the petal between the sepals 2 and 5, and the petal between sepal 1 and 3); consequently two antesepalous stamens have become displaced. The derivation of octandry from a diplostemonous ancestry, and reduction of the petal are discussed. The triangular gynoecium has a strong impact in obliquely reorganizing the symmetry of the flower, loss of organs, and shifts of stamens. The so-called septal slits occurring within the style are a deepreaching non-nectariferous extension of the stigma. Alternating locular furrows are present which could play a role as pollen transmitting tissue and in the loculicid dehiscence of the capsule.     

Elucidating the unusual floral features of Swartzia dipetala (Fabaceae)

In this study, we evaluated the floral ontogeny of Swartzia dipetala, which has peculiar floral features compared with other legumes, such as an entire calyx in the floral bud, a corolla with one or two petals, a dimorphic and polyandrous androecium and a bicarpellate gynoecium. We provide new information on the function of pollen in both stamen morphs and whether both carpels of a flower are able to form fruit. Floral buds, flowers and fruits were processed for observation under light, scanning and transmission electron microscopy and for quantitative analyses. The entire calyx results from the initiation, elongation and fusion of three sepal primordia. A unique petal primordium (or rarely two) is produced on the adaxial side of a ring meristem, which is formed after the initiation of the calyx. The polyandrous and dimorphic androecium also originates from the activity of the ring meristem. It produces three larger stamen primordia on the abaxial side and numerous smaller stamen primordia on the adaxial side. These two types of stamens bear morphologically similar ripening pollen grains. However, prior to the dehiscence of thecae and presentation of pollen in the anther, only the pollen grains of the larger stamens contain amyloplasts. Two carpel primordia are initiated as distinct protuberances, alternating with the larger stamens, in a slightly inner position in the floral meristem, constituting the bicarpellate gynoecium. Both carpels are able to form fruit, although only one fruit is generally produced in a flower. The increase in gynoecium merism probably results in an increase in the surface deposition of pollen grains and consequently in the chance of pollination. This is the first study to thoroughly investigate organogenesis and the ability of the carpel to form fruit in a bicarpellate flower from a member of Fabaceae, in addition to the pollen ultrastructure in the heteromorphic stamens associated with the ‘division of labour’ sensu Darwin. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 303–320.     

Floral Development and Anatomy ofMoringa oleifera(Moringaceae): What is the Evidence for a Capparalean or Sapindalean Affinity?

Floral development and anatomy ofMoringahave been investigatedin the context of the disputed view of a capparalean affinity.Flowers arise in terminal or axillary panicles. Sepals arisesequentially and petals simultaneously. Antepetalous stamensarise simultaneously and precede the antesepalous staminodes,which emerge sequentially. Within their respective whorls, thepetals and stamens become twisted along different orientations.The gynoecium develops as a ring primordium on which three carpellarylobes become demarcated simultaneously. A saccate ovary bearsnumerous ovules on a parietal placentation and is topped bya hollow style. The interpretation of laminal placentation isdenied. Monothecal anthers are formed by the failure of onehalf to initiate. The flowers present a peculiar form of zygomorphyrunning transversally from the petal between sepals 3 and 5to sepal 4. The shape and position of petals and stamens isrelated to a pollen presentation mechanism with bowl-shapedanthers on different levels. The floral anatomy also reflectsthe zygomorphy of the flower. AlthoughMoringashares importantmorphological features with certain members of the Sapindalesand Capparales, differences in ontogeny make a close relationshipwith either Capparales or certain Sapindales appear uncertain.Copyright1998 Annals of Botany Company Moringa,Moringaceae, Capparales, Sapindales, floral ontogeny, floral anatomy.     

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.     

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.     

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.     

Trends in evolution of floral ontogeny in Cassia sensu stricto,Senna, and Chamaecrista (Leguminosae: Caesalpinioideae: Cassieae: Cassiinae); a study in convergence

Distinctions in floral ontogeny among three segregate genera (Cassia sensu stricto, Chamaecrista, and Senna) of Cassia L. support their separation. In all species studied, the order of floral organ initiation is: sepals, petals, antesepalous stamens plus carpel, and lastly antepetalous stamens. Sepal initiation is helical in all three genera, which however differ in whether the first sepal is initiated in median abaxial position (Senna), or abaxial and off-median (Cassia javanica), a rare character state among legumes. Order of petal initiation varies: helical in Senna vs. unidirectional in Cassia and Chamaecrista. Both stamen whorls are uniformly unidirectional. Intergeneric ontogenetic differences occur in phyllotaxy, inflorescence architecture, bracteole formation, overlap of initiation among organ whorls (calyx/corolla in Cassia; two stamen whorls in Chamaecrista), eccentric initiation on one side of a flower, anther attachment, anther pore structure, and precocious carpel initiation in Senna. The asymmetric corolla and androecium in Chamaecrista arise by precocious organ initiation on one side (left or right). The poricidal anther character can result from differing developmental pathways: lateral slits vs. sealing of lateral sutures; clasping hairs vs. sutural ridges; terminal pores (one or two) vs. none; and clamp layer formation internally that prevents lateral dehiscence. Genera differ in corolla aestivation patterns and in stigma type. Convergence is shown among the three genera, based on intergeneric dissimilarities in early floral ontogeny (floral position in the inflorescence, bracteole presence, position of the first sepal initiated, order of petal initiation, asymmetric initiation, overlap between whorls, anther morphology, and time of carpel initiation) resulting in similarities at anthesis (showy, mostly yellow salverform flowers, heteromorphic stamens, poricidal anther dehiscence, bee pollination, and chambered stigma).     

OVERLAPPING ORGAN INITIATION AND COMMON PRIMORDIA IN FLOWERS OF PISUM SATIVUM (LEGUMINOSAE: PAPILIONOIDEAE)

The floral ontogeny of Pisum sativum shows a vertical order of succession of sepals, petals plus carpel, antesepalous stamens, and antepetalous stamens. Within each whorl, unidirectional order is followed among the organs, beginning on the abaxial side of the flower, as in most papilionoids. Unusual features include the four common primordia which precede initiation of discrete petal and antesepalous stamen primordia, and the marked overlap of organ initiations between whorls which are usually separately initiated. The stamens arise in free condition, then become diadelphous by intercalary growth at the base of nine stamens, and finally become pseudomonadelphous by surface fusion between the vexillary stamen filament and the adjacent edges of the filament tube. The early initiation of the carpel is not unique among papilionoids, but is somewhat unusual.     

DEVELOPMENT AND VASCULATURE OF THE FLOWERS OF LOPHOTOCARPUS CALYCINUS AND SAGITTARIA LATIFOLIA (ALISMACEAE)

The development of the bisexual flower of Lophotocarpus calycinus and of the unisexual flowers of Sagittaria latifolia has been observed. In all eases floral organs arise in acropetal succession. In L. calycinus, after initiation of the perianth, the first whorl of stamens to form consists of six stamens and is ordinarily followed by two alternating whorls of six stamens each. The very numerous carpels arc initiated spirally. In the male flower of S. latifolia the androecium develops in spiral order. A few rudimentary carpels appear near the floral apex after initiation of the stamens. There are no staminodia. The female flower has a similar developmental pattern to that of Lophotocarpus except that a prominent residual floral apex is left bare of carpels. The vascular system in all flowers is semiopen, with vascular bundles passing to the floral organs in a pattern unrelated to the relative positions of those organs. The androecia of these two taxa are similar to those of some Butomaceae and relationships based on ontogeny and morphology are suggested. The gynoecia are meristically less specialized but morphologically more specialized than the gynoecia of Butomaceae.     

Floral development and systematics ofCistaceae

The floral development of representatives of six genera ofCistaceae has been studied. Calyx development involves the formation of a ring primordium in several taxa. Androecium development in species with intermediate or higher stamen numbers starts with the formation of a ring meristem on which the stamens are initiated in a centrifugal direction. In many taxa five alternipetalous leading stamen primordia can be observed. In the apetalous (cleistogamous) flowers ofTuberaria inconspicua androecium development appears to be unordered; this is probably due to the lack of petals. InLechea intermedia (also cleistogamous) the corolla is trimerous and three complex stamen primordia are produced, which give rise either to one or three stamens. Relationships withinCistaceae are discussed. Floral development inCistaceae is compared with that in otherMalvanae. Among the eight families ofMalvanae from which information on floral development is availableCochlospermaceae andBixaceae exhibit the greatest similarities toCistaceae. InCistaceae the leading stamen primordia are alternipetalous. InBixa the same condition seems to be present. InMalvales s. str. mostTiliaceae also show earliest stamen initiation in alternipetalous sectors, whereas the stamens of the innermost alternipetalous position are retarded early or even suppressed inSterculiaceae, Bombacaceae, andMalvaceae. WithinMalvales s. str. the diversity of androecial developmental patterns seems to decrease inBombacaceae andMalvaceae due to increasing synorganization in the mature androecium. The derivation of polyandry inMalvanae from diplo- or obdiplostemony is discussed by comparison with the sister clades ofMalvanae as shown in recentrbcL studies (i.e.Sapindales, Rutales, the glucosinolate producing clade, andMyrtales).     

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.     

Evolution of perianth and stamen characteristics with respect to floral symmetry in Ranunculales

BACKGROUND AND AIMS: Floral symmetry presents two main states in angiosperms, namely polysymmetry and monosymmetry. Monosymmetry is thought to have evolved several times independently from polysymmetry, possibly in co-adaptation with specialized pollinators. Monosymmetry commonly refers to the perianth, even though associated androecium modifications have been reported. The evolution of perianth symmetry is examined with respect to traits of flower architecture in the Ranunculales, the sister group to all other eudicots, which present a large diversity of floral forms. METHODS: Characters considered were perianth merism, calyx, corolla and androecium symmetry, number of stamens and spurs. Character evolution was optimized on a composite phylogenetic tree of Ranunculales using maximum parsimony. KEY RESULTS: The ancestral state for merism could not be inferred because the basalmost Eupteleaceae lack a perianth and have a variable number of stamens. The Papaveraceae are dimerous, and the five other families share a common trimerous ancestor. Shifts from trimery to dimery (or reverse) are observed. Pentamery evolved in Ranunculaceae. Ranunculales except Eupteleaceae, present a polysymmetric ancestral state. Monosymmetry evolved once within Papaveraceae, Ranunculaceae and Menispermaceae (female flowers only). Oligandry is the ancestral state for all Ranunculales, and polyandry evolved several times independently, in Papaveraceae, Menispermaceae, Berberidaceae and Ranunculaceae, with two reversions to oligandry in the latter. The ancestral state for androecium symmetry is ambiguous for the Ranunculales, while polysymmetry evolved immediately after the divergence of Eupteleaceae. A disymmetric androecium evolved in Papaveraceae. The ancestral state for spurs is none. Multiple spurs evolved in Papaveraceae, Berberidaceae and Ranunculaceae, and single spurs occur in Papaveraceae and Ranunculaceae. CONCLUSIONS: The evolution of symmetry appears disconnected from changes in merism and stamen number, although monosymmetry never evolved in the context of an open ground plan. In bisexual species, monosymmetry evolved coincidently with single spurs, allowing us to propose an evolutionary scenario for Papaveraceae.     

Floral Morphogenesis of Anemone rivularis Buch.-Ham. ex DC. var.flore-minore Maxim. (Ranunculaceae) with Special Emphasis on Androecium Developmental Sequence

The floral morphogenesis and androecium developmental sequence of Anemone rivularis Buch.-Ham. ex DC. var. flore-minore Maxim. were observed under a scanning electron microscope (SEM)and by means of histological methods in order to expand our knowledge of the morphogenesis and development of the floral organs of the Ranunculaceae. The initiation of the floral elements is a centripetal spiral and the direction of the spiral is clockwise or anti-clockwise. However, the development of the androecium is highly unusual: in a longitudinal series of four stamens, the second stamen develops first from the inner to outer, then the third one, the fourth one and the first one in turn. The microsporogenesis and anther maturation follows the same developmental sequence. The tepals are different from the bracts and the stamens in both shape and size in the early developmental stage, but there is no difference between the stamens and carpels in the early developmental stage. Therefore, we established a spatio-temporal process of the floral morphogenesis of4. rivularis var.flore-minore and offer another meaning of the floral diversity patterns attributed to the level of the genus.     

Androecium and floral nectaries ofHarungana madagascariensis (Clusiaceae)

The mature flower ofHarungana madagascariensis (Choisy)Poir. has an androecium of five antipetalous fascicles, consisting of four stamens each. The stamen fascicles alternate with five indented nectary scales. A SEM-study of the floral development, as well as a study of the floral anatomy was carried out to understand whether the nectariferous scales represent staminodia or are receptacular in nature and consequently whether or not the androecium ofHarungana, and theClusiaceae in general, is originally diplostemonous. The five petals originate by the splitting of petal-stamen complexes. Next the upper part of each complex differentiates basipetally in four stamens. The stamens remain fascicled and are lifted on a long stalk at maturity. Five carpel primordia are initiated united in a low ringwall. The five nectary scales appear after carpel inception and develop an external morphology reminiscent of anthers. The floral anatomy reveals an independent origin of sepal median traces and common sepal lateral traces, free petal traces, stamen fascicle traces and alternating vascular tissue which supplies the nectaries. The petal-stamen complexes are the result of a retardation in petal inception, linked with the absorption of petal tissue into the stamen primordia. The development of the stamen fascicles is discussed; it is suggested that they are of a secondary nature and do not appear as a reduction from a multistaminate androecium. The external morphology and vascular anatomy of the scales speaks in favour of a staminodial nature. The comparison with some other species of theClusiaceae gives evidence of a diplostemonous ancestry of the androecium.     

THE DEVELOPMENTAL BASIS OF TRISTYLY IN EICHHORNIA PANICULATA (PONTEDERIACEAE)

Eichhornia paniculata is a tristylous, self-compatible, emergent aquatic. A given plant produces flowers with either long, mid or short styles and two levels of stamens equal in length to the styles not found in that flower. Flowers of each morph have two whorls of three tepals, six stamens and three fused carpels. The six stamens differentiate into two sets of three stamens each. A relatively short set, having either short- or mid-level stamens, occurs on the upper side of the flower, while a relatively long set, having either mid- or long-level stamens, occurs on the lower side. Stamen level depends on differences among stamens in filament length and position of insertion on the floral tube. Floral parts arise in whorls of three, but the two stamen whorls do not form the two sets of stamens found in each mature flower. Instead, stamens from both whorls make up a given set. Floral differences among morphs are not present at flower origin or floral organ initiation. Morphological differences arise first among stamen sets. The two sets within a flower differ prior to meiosis in the size, number, and timing of comparable developmental events in the sporogenous cells. After these initial differences arise, anther size diverges. In later developmental stages differences in filament and floral tube length, cell size, and cell number, as well as differences in the length, cell size, and cell number of styles, develop among morphs. This sequence of developmental events suggests that the genes controlling development in different morphs do not control flower and floral organ initiation but are first morphologically visible in sporogenous cell differentiation.     

Studies in the Lauraceae: V. Comparative Morphology of The Flower

The morphological nature of the various parts of the lauraceousflower has been discussed on the basis of available evidencefrom floral anatomy and ontogeny. Evidence from floral anatomysupports the view that both whorls of perianth are homologousand that the inner whorl does not represent modified stamens.The perianth has not attained a level of differentiation intosepals and petals in a real sense. The lauraceous flower mighthave had staminal appendages in all the four whorls in the ancestralcondition. The living genera represent varying degrees of reduction.These appendages are regarded as modified stamens. The stamensin the family cannot be considered as reduced branch systems.The androecium is interpreted as consisting of stamen fascicles.The two-trace carpel is common in the family. Evidence fromontogeny and vascular anatomy makes it improbable that the gynoeciumconsists of more than one carpel. The carpel is essentiallyof the conduplicate type.     

Androecial Development in Six Polyandrous Genera Representing Five Major Groups of Palms

Floral organogensis is described for six polyandrous generarepresenting borassoid, caryotoid, ceroxyloid, inarteoid, andgeonomoid major groups of palms. In all, three sepals and threepetals arise from dome-shaped floral apices in alternate pseudo-whorls.After petal inception, the floral apex expands in a differentway in each major group. Different numbers and arrangementsof stamens develop in antesepalous (AS) and antepetalous (AP)positions Primary pnmordia are sometimes distinct, and stamenpnmordia vary in form In borassoid and caryotoid palms, AS whorlsalways consist of three stamens, but several stamens arise inthe lower, wider AP positions Ceroxylon is characterized bylarge primary primordia with two to three stamens developingopposite each petal and, in species with more than 12 stamens,two to three also opposite each sepal. Several stamens ariseon distinctive truncate, AS primordia in a definite patternthat is repeated in AP positions in inarteoid palms In polyandrousgeonomoid genera, stamens arise in AS and AP arcs on a flattrilobed floral apex. Previous work has shown similarities instamen inception in arecoid genera to that in borassoid andcaryotoid palms, and centrifugal initiation in all phytelephantoidpalms. All polyandrous taxa, except phytelephantoid palms, exhibita basic tnmery. The different patterns of apical expansion andstamen arrangement indicate that polyandry has arisen separatelyin each major group of palms. The mode of apical expansion andthe form of the primordia appear to depend on pressures imposedon the floral apices, suggesting that specialization of inflorescencebracts and perianth segments preceded the evolution of polyandry.Correlations of vasculature with developmental patterns areindicated. Lodoicea maldivica (Gmelin) Persoon, Caryota mitis Loureiro, Ceroxylon alpinum Bonpland ex DeCandolle, Socratea exorrhiza (Martius) H. Wendland, Wettima castanea Moore and Dransfield, Welfia georgii H. Wendland ex Burret, palms, androecium, stamen development