Position Of Stamens Research Articles

Correlation between number and position of floral organs in Arabidopsis

The study of variation in number, position and type of floral organs may serve as a key to understanding the mechanisms underlying their variation, and will make it possible to improve the analysis of gene function in model plant species by means of a more accurate characterization of mutant phenotypes. The present analysis was carried out in order to understand the correlation between number and position of floral organs in Arabidopsis thaliana. An analysis of number and position of organs in flowers of wild type as well as in a series of mutations with floral organ position alterations was carried out, using light and electron microscopy. Variation common to different genotypes was analysed by means of individual diagrams, upon which generalized diagrams depicting variation in number and position of organs, were built by superimposition. It is shown that in the Arabidopsis flower a correlation exists between positions of petals and sepals, as well as between positions of stamens and carpels, whereas the position of carpels does not seem to depend on number and position of petals and stamens. This suggests that the position of organs in the basal (sepals) and apical (carpels) parts of the flower are determined before that in the intermediate zone. This assumption is consistent with the results of mathematical modelling and is supposed to be the consequence of stem-cell activity in the flower.

A note on stamen position and petal number in <I>Loranthaceae</I>

Stamen position in Loranthaceae is summarized in both the Old and New Worlds. In the former, stamens are inserted on petals at the same height in an individual flower, with very few exceptions that appear to be in basalmost genera only. In the Americas, much diversity exists in both the position and the within-flower shapes of stamens, phenomena that occur in many genera, Psittacanthus showing the greatest diversity. The dimorphic, or at least the biseriate condition is believed to be the plesiomorphic state. Some comments are added on petal numbers in the family.

Modification of flower architecture during early stages in the evolution of self-fertilization.

The evolution of selfing from outcrossing is characterized by a series of morphological changes to flowers culminating in the selfing syndrome. However, which morphological traits initiate increased self-pollination and which are accumulated after self-fertilization establishes is poorly understood. Because the expression of floral traits may depend on the conditions experienced by an individual during flower development, investigation of changes in mating system should also account for environmental and developmental factors. Here, early stages in the evolution of self-pollination are investigated by comparing floral traits among Brazilian populations of Eichhornia paniculata (Pontederiaceae), an annual aquatic that displays variation in selfing rates associated with the breakdown of tristyly to semi-homostyly. Thirty-one Brazilian populations under uniform glasshouse conditions were compared to investigate genetic and environmental influences on flower size and stigma-anther separation (herkogamy), two traits that commonly vary in association with transitions to selfing. Within-plant variation in herkogamy was also examined and plants grown under contrasting environmental conditions were compared to examine to what extent this trait exhibits phenotypic plasticity. In E. paniculata a reduction in herkogamy is the principal modification initiating the evolution of selfing. Significantly, reduced herkogamy was restricted to the mid-styled morph and occurred independently of flower size. Significant genetic variation for herkogamy was detected among populations and families, including genotypes exhibiting developmental instability of stamen position with bimodal distributions of herkogamy values. Cloned genets exposed to contrasting growth conditions demonstrated environmental control of herkogamy and genotypic differences in plasticity of this trait. The ability to modify herkogamy independently of other floral traits, genetic variation in the environmental sensitivity of herkogamy, and the production of modified and unmodified flowers within some individuals, reveal the potential for dynamic control of the mating system in a species that commonly confronts heterogeneous aquatic environments.

Morphological study of sex organs and pollen grain of chosen wild species from Solanaceae family in Iraq

In this study four species from Solanaceae family was conducted. These four species belong to four different genera (Solanum L. ? Physalis L. ?Withania Pauq. ? Lycium L.) The study included morphological characters of sex organs and their pollen grains for these Iraqi wild plants.The results showed that the position of epipetalous stamens , the shape of anther, their dimensions ,and the length of filaments are important taxonomical characters .On the others hand the shape of their ovaries and stigmas are also important characters in distinguish between these four species .Pollen grains are similar in their general shapes and polarities, they have three germinal furrows and germinal apertures, so they are minor in distinguish between these four species.

Morphological study of sex organs and pollen grain of chosen wild species from Solanaceae family in Iraq

In this study four species from Solanaceae family was conducted. These four species belong to four different genera (Solanum L. ? Physalis L. ?Withania Pauq. ? Lycium L.) The study included morphological characters of sex organs and their pollen grains for these Iraqi wild plants.The results showed that the position of epipetalous stamens , the shape of anther, their dimensions ,and the length of filaments are important taxonomical characters .On the others hand the shape of their ovaries and stigmas are also important characters in distinguish between these four species .Pollen grains are similar in their general shapes and polarities, they have three germinal furrows and germinal apertures, so they are minor in distinguish between these four species.

The effect of nectar production to the gathering behaviour of honeybees and to the foraging activity of wild bees at apple flowers

Intensity of bee visitation (honeybees and wild bees), foraging behaviour of honeybees and nectar parameters (nectar production, sugar concentration, sugar content in nectars) were inspected at 18 apple cultivars for three consecutive years. Honeybee visitation was calculated to be some 3.07 bee visits at a single apple flower a day but wild bee activity was very low, only some 0.11 wild bee visits per flower per day.
 The nectar production (nectar content) of apple flowers was fairly different according to the cultivars and the nectar production (nectar content) of flowers was negatively correlated with the sugar concentration in nectar. Interestingly, at the majority of the inspected 18 cultivars the nectar production has shown minor or no changes in the morning and at the afternoon. The nectar production (nectar content) of flowers clearly encouraged the total bee activity at the inspected cultivars (r = 0.54). Bees visited abundant nectars with greater sugar concentration most intensely than lees abundant nectars with smaller sugar concentration.
 Nectar parameters, however, affected the activity of honeybees with different types of gathering behaviour in different way. More intense activity by pollen gatherer and mixed behaviour honeybees was observed at cultivars producing abundant nectar (pollen gatherers: r = 0.65, mixed behaviour: r = 0.79). The activity of pollen gatherer honeybees and of mixed behaviour bees, on the other hand, was negatively correlated to the sugar concentration in nectar (pollen gatherers: r = -0.51, mixed behaviour: r = -0.73). This can be explained by the fact that their behaviour was much more affected by the amount of pollen than by any nectar parameters. Accordingly, "mixed behaviour honeybees" should probably rather be called as "pollen gatherers with nectar load" instead of "nectar gatherers with pollen load", as widely used in literature. The activity of ineffective side worker nectar gatherers was greatly encouraged by the sugar concentration in nectar (p = 0.63), similarly to the pure (top) nectar gatherer honeybees (r = 0.72). There was a negative relationship between the nectar production (nectar content) of flowers and the activity of these behaviour classes (nectar gatherers: r = -0.47, side workers: r = -0.36).
 Concluding the findings we can state that the activity of pollen gatherers and mixed behaviour honeybees is strongly encouraged by greater nectar production (greater nectar content) of apple flowers. Their activity, however, is mostly dependent firstly on the amount of pollen. This is the reason why the sugar concentration is in a negative relationship to the activity of pure pollen gatherers and mixed behaviour bee. On the other hand, pure nectar gatherers and side worker nectar gatherers are greatly encouraged by the sugar concentration of apple nectar the amount of nectar was not a definite influence on their activity.
 Side worker honeybees occurred at each cultivar inspected, however, their ratio varied widely among cultivars. So we can draw the conclusion that, in contradiction with earlier believes, side worker nectar gathering is a general phenomenon at apple flowers. The activity of side workers depends first of all on the relative position of stamens and petals; however, low sugar concentration of nectars can probably moderate their activity but probably do not affect pollen gatherers and mixed behaviour bees.
 Wild bee visitation was very low; the wild bee species observed (Osmia cornuta, Andrena flavipes, Anthophora acervorum, Bombus terrestris, Bombus lapidarius and Halictus simplex) comprised some 3.44 per cent of the total bee visitation at apple flowers only. Wild bee visitation was in a positive correlation with the nectar production (nectar amount) of flowers (r = 0,4) and with the sugar content of nectar (r = 0.46) but it was negatively correlated with the sugar concentration in nectar (r = -0,27).
 Our result calls the attention to the importance of nectar parameters in the effective honeybee pollination of apple plantations. Most effective pollinating activity of honeybees can be expected in plantations with cultivars of high nectar production because this feature seem so encourage the activity of those behaviour classes (pure pollen gatherers and mixed behaviour bees) that are the most effective pollinating agents among honeybees.

Early floral development and androecium organization in Fouquieriaceae (Ericales)

Early floral development with focus on the androecium was studied with the help of scanning electron microscopy and serial microtome sectioning in Fouquieria columnaris and F. splendens. Perianth organs appear in a spiral pattern on the floral apex. The spiral may be a clockwise or anti-clockwise. The androecium is best interpreted as two-whorled with all the stamens arranged in a single series. In F. splendens, two or more of the five epipetalous stamen positions are doubled, i.e. they are occupied by stamen pairs. Unusual features in the floral development of Fouquieriaceae include (1) a strong spiral component even in whorled organ categories and (2) a pronouncedly asymmetric floral apex during an early phase of floral development. From a phylogenetic point of view, it seems plausible that the common ancestor of Fouquieriaceae and its sister family Polemoniaceae was characterized by two alternating, pentamerous stamen-whorls.

Floral anatomy in Dypsis (Arecaceae–Areceae): a case of complex synorganization and stamen reduction

Male (staminate) flowers of Dypsis possess either six or three stamens and/or staminodes, in contrast to most other palms, in which the basic stamen number is six (although polyandry is also common in palms). Significant variation among the tristaminate forms, both in stamen morphology and stamen position with respect to the perianth parts, indicates that stamen reduction from six to three has occurred more than once, and possibly several times within Dypsis. A few species include teratological forms with zygomorphic flowers; for example, Dypsis lantzeana normally possesses three antesepalous stamens, but in some specimens only the median outer (abaxial) stamen is expressed, perhaps indicating incipient zygomorphy correlated with complex synorganization. Inclusion of earlier historic genera such as Neophloga and Chrysalidocarpus within a broadly circumscribed Dypsis appears to be justified, although the informal taxonomic groupings within Dypsis require review, in particular the taxonomic significance of the different types of anther morphology. The discovery here that adnation of staminodes to the pistillode (complex synorganization) occurs in species other than D. mirabilis opens further questions about the taxonomic utility of this character in Dypsis, in which stamen/staminode development and adnation are apparently unusually labile. Such androecial–gynoecial adnation is otherwise rare in palms, as also in other monocots, in which probably the best-known example occurs in orchids. Septal nectaries are present in some, but not all, staminate flowers in species of Dypsis. Dypsis bejofo is exceptional in that in staminate flowers the pistillode is distally bulbous and bears three prominent modified supralocular septal nectaries. Female (pistillate) flowers in Dypsis are syncarpous, normally pseudomonomerous (as in many other Arecoideae), and possess septal nectaries that effectively delimit the carpel margins and indicate insect pollination. There is a central solid transmitting tissue that extends from the placenta to three stylar canals. The stylar canals of the two sterile carpels are apparently functional, in addition to that of the fertile carpel. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 143, 115−133.

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.

The Ontogenetic Basis for Floral Diversity in the Baeckea Sub-Group (Myrtaceae)

Androecial morphology differs widely amongst flowers of the Australasian Myrtaceae. Differences occur in the number, position and arrangement of stamens. Mature flowers of the Baeckea sub-group genera are superficially similar at maturity, but are very diverse in terms of their androecial structure. Floral development of six taxa in the informal Baeckea sub-group is described, and three developmental factors are identified as major contributors to mature androecial pattern. These are: differences in (i) timing of primordia initiation, (ii) duration of primordia initiation, and (iii) enlargement of the hypanthium subsequent to stamen initiation. Late or early initiation of stamens affects where the first stamens are formed, and how many stamens are produced, primarily due to available space on the floral meristem. Total number of stamens produced is influenced by the duration of stamen production. How the hypanthium enlarges following stamen initiation determines the final arrangement of the stamens in the mature flower if the bud expands more in some areas than others, the stamens will be shifted into different positions around the flower. Minor changes in any of these developmental factors result in significantly different flower morphology. Understanding these potentially variable and reversible developmental processes is important for assessing mature flower characters for phylogenetic analysis, and investigating mechanisms of evolutionary change.

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

Abstract Floral development and anatomy of Moringa have been investigated in the context of the disputed view of a capparalean affinity. Flowers arise in terminal or axillary panicles. Sepals arise sequentially and petals simultaneously. Antepetalous stamens arise simultaneously and precede the antesepalous staminodes, which emerge sequentially. Within their respective whorls, the petals and stamens become twisted along different orientations. The gynoecium develops as a ring primordium on which three carpellary lobes become demarcated simultaneously. A saccate ovary bears numerous ovules on a parietal placentation and is topped by a hollow style. The interpretation of laminal placentation is denied. Monothecal anthers are formed by the failure of one half to initiate. The flowers present a peculiar form of zygomorphy running transversally from the petal between sepals 3 and 5 to sepal 4. The shape and position of petals and stamens is related to a pollen presentation mechanism with bowl-shaped anthers on different levels. The floral anatomy also reflects the zygomorphy of the flower. Although Moringa shares important morphological features with certain members of the Sapindales and Capparales, differences in ontogeny make a close relationship with either Capparales or certain Sapindales appear uncertain.

Early development of androecia in polystemonous Hydrangeaceae

Polystemonous androecia are diverse in both number and position of stamens. This investigation of polystemonous Hydrangeaceae uses developmental data to characterize (1) the range of developmental variations that account for the diverse androecial patterns and (2) how the expressions of polystemony among Hydrangeaceae compare to those found generally among other angiosperms and especially in their sister family, the Loasaceae, some of which have particularly complex androecia. All polystemonous Hydrangeaceae share the common element of stamen clusters in antesepalous positions. In each of these taxa, the first stamens are initiated opposite the medians of the sepals. Subsequently, stamens form laterally on the flanks of the initial antesepalous stamens, giving rise to the clusters designated as antesepalous triplets. The simplest elaborations based on those common initial developmental steps include (1) adding additional lateral flanking stamens and (2) adding a single stamen in each antepetalous position between adjacent antesepalous groups. More complex elaborations are characteristic of (1) Carpenteria and Philadelphus, which form common primordia at the beginning of androecial development and, subsequently, have stamen primordia form on them, and (2) Deinanthe, which has an elongate hypanthial region on which numerous whorls of stamens are initiated. Carpenteria is unique among Hydrangeaceae in having groups of stamens that are initiated centrifugally in antepetalous positions, and this is similar to complex elements found among some Loasaceae. Generally, the polystemony of Hydrangeaceae that is based in the formation of antesepalous triplets is very similar to that found to evolve in parallel among various clades of rosids and asterids.

A Study of Floral Morphological Diversity in Phytolacca (Phytolaccaceae) Based on Early Floral Ontogeny

The floral ontogeny of four species of Phytolacca (P. acinosa, P. clavigera, P. dodecandra, and P. americana) shows major differences in the number and position of stamens and carpels. Five sepals are always formed in a 2/5 sequence. The number of stamens is mostly eight, with a sequential initiation: six outer stamens are arranged in three pairs opposite sepals 1-3; single stamens stand opposite sepals 4-5, except for P. americana, where all antesepalous stamens are positioned in pairs (10 stamens rather than eight). The stamens of the first, second, and third pair arise simultaneously as independent entities. The stamens of the third pair occasionally arise sequentially and are displaced in relation to the third sepal. Stamens opposite sepals 4 and 5 follow sequentially. The delayed plastochron of the stamens opposite sepal 3 indicates that the pentamerous flower has been derived from a trimerous precursor. Phytolacca dodecandra has 10 stamens arising in a different sequence: the five inner stamens are alternisepalous and the five outer, antesepalous, thus resembling diplostemony. The alternisepalous stamens correspond positionally to the two pairs opposite sepals 1-2 in other species, plus one stamen between sepals 3 and 5. The outer antesepalous stamens appear later and correspond to single stamens opposite sepals 3-4-5 in the other species, with two extra stamens opposite sepals 1-2. In other species a variable number of outer stamens may arise centrifugally in alternate whorls. The number of carpels corresponds with the number of stamens in the inner androecial whorl. Each carpel consists of a free abaxial part and an adaxial, continuous ovule-bearing part. Our data of the androecial ontogeny refute the existence of diplostemony in the Phytolaccaceae, with P. dodecandra occupying a pivotal position. It is suggested that the paired arrangement of stamens in Phytolacca is a basic condition in the family and is not the result of dédoublement. The centrifugal initiation of outer stamens is believed to reflect a reversal in the direction of stamen initiation and is not linked with a secondary stamen multiplication.

Breeding Systems of Ardisia Sw. (Myrsinaceae)

Five species (A. escallonioides Schltdl. & Cham., A. hirtella Lundell, A. elliptica Thunb., A. sieboldii Miq., and A. wallichii A.DC.) from three subgenera in the genus Ardisia (Myrsinaceae) were examined for self-compatibility, agamospermy, and autogamy using hand-pollination and pollinator-exclusion experiments on both garden plants and wild populations. All five species are self-compatible but not agamospermous. Four of the five species exhibited autogramy. Autogamy was strongly associated with stamen position, anther dehiscence type, protogyny, and inflorescence type. Because self-compatibility is widespread across different subgenera, it may be a general characteristic of the genus Ardisia. The potential impact of self-compatibility on the mating system and population genetic structure is discussed.

Quantitative genetics of stamen fertility in Spergularia salina (Caryophyllaceae)

Heritability of stamen fertility was studied in Spergularia salina (Caryophyllaceae), a selfing annual that shows extensive phenotypic variation in stamen fertility. Variation within and among 70 maternal families, derived from plants representing two natural populations from Sweden, was used to estimate heritabilities of stamen fertility for each of the 10 stamen positions in the flower. The hierarchical design of the study allowed partitioning of variation among four levels of organization using nested analysis of variance. Heritabilities ranged from 0.27 to 0.65 for stamen positions in the antipetalous whorl of stamens and from 0.18 to 0.67 for positions in the antisepalous whorl. When stamen fertility was pooled across all stamen positions of a flower, the heritability was 0.73 in both populations. The nested ANOVA indicated that antipetalous stamen positions have comparatively higher proportions of among-family and among-population variation than the antisepalous stamen positions. Furthermore, highly significant genetic correlations exist between the two antisepalous stamen positions STA 2 and STA 8 and among the other eight positions but not so between these two groups. The relationship between tetraploidization and stamen number reductions in Caryophyllaceae is discussed. Key words: Spergularia salina, stamen fertility, stamen position, heritability, hierarchical analysis of variance, quantitative genetics.

Floral Development and Homeosis in Actaea rubra (Ranunculaceae)

Actaea rubra is a member of the Ranunculaceae in which the number and positions of petals are variable. To understand the process by which this variation arises, we used epi-illumination microscopy to study floral development in the species. We found that four sepal primordia initiate in two pairs, one outer and one inner. Then four primordia form in alternation with the sepal primordia, followed by the initiation of six primordia in opposition to the sepal primordia (one primordium opposite each outer sepal primordium, and two opposite each inner sepal primordium). These first 10 small, rounded primordia can develop into either petals or stamens, but they cannot be discerned in early stages because the primordia are very similar in size and shape. Subsequently, numerous primordia that usually develop into stamens initiate in alternation with previously formed primordia, and the floral apex terminates in a crescent-shaped gynoecial primordium. Petal and stamen primordia can be distinguished in later stages when petal primordia are small and flattened in appearance, whereas stamen primordia have anther sacs. At maturity petals are small, white, and spatulate-shaped, and stamens have long, slender filaments and oval anthers. Examination of these later stages showed that the number and positions of petals are not constant. We therefore mapped petal and stamen positions in more mature floral buds and found that petals most frequently occupied the positions that alternate with the sepals. However, a comparison of the positions that petals and stamens occupy in different flowers showed that petals could form in what were usually stamen positions, and stamens could form in what were usually petal positions. We interpret this as an example of homeosis occurring within and among plants of A. rubra. When the floral morphology of Actaea is compared with that of related taxa, various phylogenetic interpretations of homeosis can be hypothesized, depending on the putative outgroup condition.

Quantitative genetics of stamen number in the selfing Scleranthus annuus (Caryophyllaceae)

Heritability of stamen fertility—different scores were given to sterile stamens developed to different degrees as well as to fertile stamens with one or two pollen sacs—was studied in Scleranthus annuus (Caryophyllaceae), a selling annual that shows extensive phenotypic variation in stamen fertility. Variation within and among 172 maternal families, derived from plants representing 20 natural populations from southern Sweden, was used to estimate heritabilities of stamen fertility for stamens/staminoids at each of the ten stamen positions in the flower. The hierarchical design of the study allowed partitioning of variation at four levels of organization using nested analysis of variance. Heritabilities ranged from 0.631 to 0.714 for stamen positions in the outer whorl of stamens and from 0.235 to 0.555 for positions in the inner whorl. When stamen fertility was pooled across all stamen positions of a flower, the heritability was 0.807. The nested ANOVA indicated that stamen positions in the outer whorl have comparatively higher proportions of among‐family and among‐population variation than those in the inner whorl. Furthermore, highly significant genetic correlations exist among stamen positions within the inner whorl and among positions within the outer whorl, but not so between positions from each of the two whorls.

Quantitative Genetics of Stamen Number in the Selfing Scleranthus annuus (Caryophyllaceae)

Heritability of stamen fertility—different scores were given to sterile stamens developed to different degrees as well as to fertile stamens with one or two pollen sacs—was studied in Scleranthus annuus (Caryophyllaceae), a selling annual that shows extensive phenotypic variation in stamen fertility. Variation within and among 172 maternal families, derived from plants representing 20 natural populations from southern Sweden, was used to estimate heritabilities of stamen fertility for stamens/staminoids at each of the ten stamen positions in the flower. The hierarchical design of the study allowed partitioning of variation at four levels of organization using nested analysis of variance. Heritabilities ranged from 0.631 to 0.714 for stamen positions in the outer whorl of stamens and from 0.235 to 0.555 for positions in the inner whorl. When stamen fertility was pooled across all stamen positions of a flower, the heritability was 0.807. The nested ANOVA indicated that stamen positions in the outer whorl have comparatively higher proportions of among-family and among-population variation than those in the inner whorl. Furthermore, highly significant genetic correlations exist among stamen positions within the inner whorl and among positions within the outer whorl, but not so between positions from each of the two whorls.

Inheritance of mating-system modifier genes in Eichhornia paniculata (Pontederiaceae)

The evolutionary breakdown of tristyly to predominant self-fertilization in Eichhornia paniculata (Pontederiaceae) is associated with the spread and fixation of floral variants of the mid-styled morph (M) with modified short-level stamens. Reduced stigma–anther separation in the variants results in a high degree of self-fertilization. To investigate if the genetic basis of mating-system modification differs among floral variants from different parts of the geographical range of the species we performed controlled crosses on genotypes from six populations from N.E. Brazil and Jamaica. Measurements of floral traits in self and F1 crosses grown under uniform glasshouse conditions demonstrated that the gene(s) modifying stamen position in the M morph are largely recessive, have no apparent phenotypic effects on other floral characters and are only expressed in the M morph. Crosses between modified genotypes from northern and southern parts of N.E. Brazil resulted in F1 progeny with unmodified flowers, indicating that different recessive genes are responsible for stamen modification in the two regions. Crosses between modified genotypes from Jamaica and the two regions of N.E. Brazil indicated a more complex basis for stamen modification in Jamaica, and confirmed that the genetic basis of selfing differed between the two regions of Brazil. Our results provide evidence that the evolution of self-fertilization in E. paniculata has occurred by different genetic pathways. In addition, the data suggest that the sequence of events commences with the fixation of recessive alleles affecting only filament length, followed by evolution at modifier loci responsible for larger phenotypic changes to floral architecture.

Homeosis in floral development of Sanguinaria canadensis and S. canadensis ‘Multiplex’ (Papaveraceae)

Sanguinaria canadensis is a member of the Papaveraceae that normally has eight petals rather than four as is usual in the family. Using epi‐illumination microscopy to study floral development, we show that the four additional petal primordia are initiated in positions that correspond to the first four stamen positions in species of the Papaveraceae with four petals. Also, these additional petal primordia share early developmental features with stamen primordia: at inception they are circular in outline, and the relationship between organ length and width while very young is similar. The developmental pathway of the additional petals combines both stamen and petal features: initially stamenlike in appearance, they develop into typical petals. The additional petals of S. canadensis can therefore be interpreted as homeotic because petal features are expressed in stamen positions. Organogenesis in the ‘Multiplex’ cultivar is similar to that of its wild progenitor, but during development all primordia in the androecial region become petals. This cultivar, as well as variants within natural populations, show that replacement of stamens with petals occurs within the species.