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PubMed2001

Photocontrol of flowering and stem extension of the intermediate-day plant Echinacea purpurea.

Intermediate-day plants (IDP) flower most rapidly and completely under intermediate photoperiods (e.g., 12-14 h of light), but few species have been identified and their flowering responses are not well understood. We identified Echinacea purpurea Moench as an IDP and, based on our results, propose a novel mechanism for flowering of IDP. Two genotypes of E. purpurea ('Bravado' and 'Magnus') flowered most completely (>/=79%) and rapidly and at the youngest physiological age under intermediate photoperiods of 13-15 h. Few (</=14%) plants flowered under 10- or 24-h photoperiods, indicating E. purpurea is a strongly quantitative IDP. Plants were also induced to flower when 15-h dark periods were interrupted with as few as 7.5 min of low-intensity lighting (night interruption, NI). Flowering was progressively earlier as the NI increased to 1 h, but was delayed when the NI was extended to 4 h. Stem length increased by >/=230% as the photoperiod or NI duration increased, until plants received a saturating duration (at 14 or 1 h, respectively). Flowering was inhibited when 16-h photoperiods were deficient in red (R, 600-700 nm) light, and was promoted when photoperiods were deficient in far-red (FR, 700-800 nm) light. Because of our results, we propose the flowering behavior of IDP such as E. purpurea is composed of two mechanisms: a light-dependent response operating through light-labile (type I) phytochrome in which flowering is inhibited by an LD, and a light-stable (type II) phytochrome (i.e., phyB, D and E) response in which flowering is promoted by a short-night.

Journal Article↗

PubMed2000

Development of Male Flowers in Zizania aquatica (North American Wild-Rice; Gramineae).

We investigated the histology and developmental morphology of flowers of wild-rice (Zizania aquatica), a member of grass subfamily Oryzoideae, to determine whether male flowers in this species develop in a manner similar to those in the subfamily Panicoideae, a group that includes many species with unisexual flowers. Zizania has evolved unisexual flowers from hermaphrodite ancestors and is only distantly related to the Panicoideae; the origins of unisexual flowers are independent in the two taxa. Ontogenetic evidence indicates that many species within the subfamily Panicoideae develop male flowers by a process similar to that already described for maize (Zea mays), a panicoid grass. Unisexual male flowers in maize initiate both the stamen (androecium) and the pistil (gynoecium), but the gynoecium aborts early in development through the death of the subepidermal cells. Cell death in gynoecia of maize is known to be controlled by the product of the gene tasselseed2 (ts2), and an orthologue of ts2 has been shown to have the same effect in the sister genus Tripsacum. It seems likely that ts2 orthologues mediate cell death throughout the Panicoideae, but the phylogenetic range of the cell death mechanism is not known. In this study we show that male flowers of Z. aquatica show neither the distinctive pattern of cell death nor the ontogenetic timing of abortion that are characteristic of male flower formation in studied species of Panicoideae. This indicates that these unisexual flowers may be produced by an entirely different mechanism from that employed by the Panicoideae. Either ts2 does not control sex expression in Zizania, or it is deployed at a different time, and possibly in different tissues, with a different histological result. Our results indicate that the independent origins of male flowers in Gramineae apparently do not have a common system of genetic control.

Journal Article↗

PubMed2001

Association of glutathione with flowering in Arabidopsis thaliana.

In order to study the relationship between GSH and flowering, wild-type and late-flowering mutant, fca-1, of Arabidopsis thaliana were treated with L-buthionine sulfoximine (BSO), a specific inhibitor of GSH biosynthesis, under long-day conditions. BSO treatment of the fca-1 mutant starting at 17 d after imbibition promoted flowering. However, when the treatment was started at 12 d after imbibition, BSO treatment at 10(-4) M resulted in an inhibition of flowering. This inhibitory effect of BSO on flowering was abolished by GSH treatment at 10(-4) M, although GSH treatment at an increased concentration of 10(-3) M clearly delayed flowering. In contrast, BSO treatment of wild-type plants starting at 12 d after imbibition promoted flowering, whose effect was abolished by GSH application. In the fca-1 mutant, whose endogenous GSH levels were high, chilling treatment lowered the GSH levels and promoted flowering, as was the case in the BSO treatment. An A. thaliana mutant, cad2-1, which has a defect in GSH biosynthesis also exhibited late flowering. The late-flowering phenotype of this mutant tended to be strengthened by BSO and abolished by GSH treatment. These results suggest that flowering is associated with the rate of GSH biosynthesis and/or the levels of GSH in A. thaliana.

Arabidopsis↗

PubMed2001

Genes encoding the vacuolar Na+/H+ exchanger and flower coloration.

Vacuolar pH plays an important role in flower coloration: an increase in the vacuolar pH causes blueing of flower color. In the Japanese morning glory (Ipomoea nil or Pharbitis nil), a shift from reddish-purple buds to blue open flowers correlates with an increase in the vacuolar pH. We describe details of the characterization of a mutant that carries a recessive mutation in the Purple (Pr) gene encoding a vacuolar Na+/H+ exchanger termed InNHX1. The genome of I. nil carries one copy of the Pr (or InNHX1) gene and its pseudogene, and it showed functional complementation to the yeast nhx1 mutation. The mutant of I. nil, called purple (pr), showed a partial increase in the vacuolar pH during flower-opening and its reddish-purple buds change into purple open flowers. The vacuolar pH in the purple open flowers of the mutant was significantly lower than that in the blue open flowers. The InNHX1 gene is most abundantly expressed in the petals at around 12 h before flower-opening, accompanying the increase in the vacuolar pH for the blue flower coloration. No such massive expression was observed in the petunia flowers. Since the NHX1 genes that promote the transport of Na+ into the vacuoles have been regarded to be involved in salt tolerance by accumulating Na+ in the vacuoles, we can add a new biological role for blue flower coloration in the Japanese morning glory by the vacuolar alkalization.

Biological Transport↗

PubMed2001

Induction of flowering in tropical trees by a 30-min reduction in photoperiod: evidence from field observations and herbarium specimens.

During the late rainy season in October 1997 we observed. over a range of >100 km, the highly synchronous emergence of flower buds in several deciduous tree species of the semi-deciduous tropical forest in Guanacaste, Costa Rica. Synchronous flowering soon after the rapid decline in day length around the September equinox and in the absence of any notable climatic cues suggested flower induction by declining photoperiod. By combining field observations and the analysis of flowering herbarium collections, we established highly synchronous flowering periods with low interannual and latitudinal variation predicted for photoperiodic flower induction for more than 25 tree species and a few herbs. We describe morphogenetic changes at the shoot apex of three species during flower induction and the suppression and induction of flowering in several herbaceous species by experimental daylight extension. The combined observations provide strong, mainly indirect evidence for photoperiodic induction of flowering in many tropical tree species. At low latitudes with annual variation in day length of 1 hour, flower induction must be caused by a decline in photoperiod of 30 min or less. This is the first report of photoperiodic control of flowering in trees.

Costa Rica↗

PubMed1999

The FLF MADS box gene: a repressor of flowering in Arabidopsis regulated by vernalization and methylation.

A MADS box gene, FLF (for FLOWERING LOCUS F ), isolated from a late-flowering, T-DNA-tagged Arabidopsis mutant, is a semidominant gene encoding a repressor of flowering. The FLF gene appears to integrate the vernalization-dependent and autonomous flowering pathways because its expression is regulated by genes in both pathways. The level of FLF mRNA is downregulated by vernalization and by a decrease in genomic DNA methylation, which is consistent with our previous suggestion that vernalization acts to induce flowering through changes in gene activity that are mediated through a reduction in DNA methylation. The flf-1 mutant requires a greater than normal amount of an exogenous gibberellin (GA3) to decrease flowering time compared with the wild type or with vernalization-responsive late-flowering mutants, suggesting that the FLF gene product may block the promotion of flowering by GAs. FLF maps to a region on chromosome 5 near the FLOWERING LOCUS C gene, which is a semidominant repressor of flowering in late-flowering ecotypes of Arabidopsis.

Arabidopsis↗

PubMed1997

Photo and hormonal control of meristem identity in the Arabidopsis flower mutants apetala2 and apetala1.

We have analyzed the contributions of phytochrome and gibberellin signal transduction to the control of flower meristem identity in the Arabidopsis mutants apetala1 (ap1) and apetala2 (ap2). ap1 flowers are partially defective for the establishment of flower meristem identity and are characterized by the production of ectopic secondary or axillary flowers and by branching. Axillary flower production is also induced in ap2-1 flowers by short-day photoperiod and is suppressed by hy1, a mutation blocking phytochrome activity. The production of axillary flower by ap2-1 is also suppressed by exogenous gibberellins and by spindly (spy), a mutation that activates basal gibberellin signal transduction in hormone-independent manner. Ectopic axillary flower production and floral branching by ap1 flowers are also suppressed by spy. We conclude that gibberellins promote flower meristem identity and that the inflorescence-like traits of ap2-1 and ap1-1 flowers are due in part to SPY gene activity.

Arabidopsis↗

PubMed2001

Perspective: Evolution of flower color in the desert annual Linanthus parryae: Wright revisited.

Linanthus parryae, a diminutive desert annual with white or blue flowers, has been the focus of a long-standing debate among evolutionary biologists. At issue is whether the flower color polymorphism in this species is the product of random genetic drift, as Sewall Wright argued, or of natural selection, as proposed by Carl Epling and his colleagues. Our long-term studies of three polymorphic populations in the Mojave Desert demonstrate that flower color is subject to selection that varies in both time and space in its direction and magnitude. For all sites taken together, blue-flowered plants produced more seeds than white-flowered plants in years of relatively low seed production, whereas white-flowered plants had higher fitness in years of high seed production. Evidence of selection on flower color was found in two of the three study sites. Differences in fitness between the color morphs were sometimes large, with selection coefficients as high as 0.60 in some years. Our longest period of observations was at Pearblossom site 1, where plants reached appreciable densities in seven of the 11 years of study. Here we found significant differences in the seed production of the color morphs in six years, with three years of blue advantage and three years of white advantage. For all sites taken together, total spring precipitation (March and April) was positively correlated with both absolute and relative seed production of the color morphs. At Pearblossom site 1, blue-flowered plants typically had a fitness advantage in years of low spring precipitation, whereas white-flowered plants had a fitness advantage in years of high spring precipitation. This temporal variation in selection may contribute to the maintenance of the flower-color polymorphism at Pearblossom site 1, whereas gene flow from neighboring populations is proposed as the principal factor maintaining the polymorphism at the other study sites. We found no significant differences between the color morphs in pollinator visitation rate or in their carbon isotope ratio, a measure of water-use efficiency. Although the mechanism of selection remains elusive, our results refute Wright's conclusion that the flower color polymorphism in L. parryae is an example of isolation by distance, a key component of his shifting balance theory of evolution.

Adaptation, Physiological↗

PubMed1997

LEAFY expression and flower initiation in Arabidopsis.

During the initial vegetative phase, the Arabidopsis shoot meristem produces leaves with associated lateral shoots at its flanks, while the later reproductive phase is characterized by the formation of flowers. The LEAFY gene is an important element of the transition from the vegetative to the reproductive phase, as LEAFY is both necessary and sufficient for the initiation of individual flowers. We have analyzed in detail the expression of LEAFY during the plant life cycle, and found that LEAFY is extensively expressed during the vegetative phase. In long days, Arabidopsis plants flower soon after germination, and this is paralleled by rapid upregulation of LEAFY. In short days, Arabidopsis plants flower several weeks later than in long days, but LEAFY expression increases gradually before flowering commences. Application of the plant hormone gibberellin, which hastens flowering in short days, enhances the gradual change in LEAFY expression observed in short days. Changes in LEAFY expression before the transition to flowering suggest that the time point of this transition is at least partly controlled by the levels of LEAFY activity that are prevalent at a given time of the life cycle. This assumption is borne out by the finding that increasing the copy number of endogenous LEAFY reduces the number of leaves produced before the first flower is formed. Thus, LEAFY combines properties of flowering-time and flower-meristem-identity genes, indicating that LEAFY is a direct link between the global process of floral induction and the regional events associated with the initiation of individual flowers.

Arabidopsis↗

PubMed2001

early bolting in short days: an Arabidopsis mutation that causes early flowering and partially suppresses the floral phenotype of leafy.

The time of flowering in Arabidopsis is controlled by multiple endogenous and environmental signals. Some of these signals promote the onset of flowering, whereas others repress it. We describe here the isolation and characterization of two allelic mutations that cause early flowering and define a new locus, EARLY BOLTING IN SHORT DAYS (EBS). Acceleration of flowering time in the ebs mutants is especially conspicuous under short-day photoperiods and results from a reduction of the adult vegetative phase of the plants. In addition to the early flowering phenotype, ebs mutants show a reduction in seed dormancy, plant size, and fertility. Double mutant analysis with gibberellin-deficient mutants indicates that both the early-flowering and the precocious-germination phenotypes require gibberellin biosynthesis. Analysis of the genetic interactions among ebs and several mutations causing late flowering shows that the ft mutant phenotype is epistatic over the early flowering of ebs mutants, suggesting that the precocious flowering of ebs requires the FT gene product. Finally, the ebs mutation causes an increase in the level of expression of the floral homeotic genes APETALA3 (AP3), PISTILLATA (PI), and AGAMOUS (AG) and partially rescues the mutant floral phenotype of leafy-6 (lfy-6) mutants. These results suggest that EBS participates as a negative regulator in developmental processes such as germination, flowering induction, and flower organ specification.

Arabidopsis↗

PubMed2004

Chrysanthemum stunt viroid disturbs the photoperiodic response for flowering of chrysanthemum plants.

Chrysanthemum ( Dendranthema grandiflorum Kitam.) is one of the qualitative short-day flowering plants. Therefore, the flowering of chrysanthemum can usually be controlled by photoperiod. However, it was noted that 'Piato' plants infected by the chrysanthemum stunt viroid (CSVd) flowered autonomously even under long-day conditions. In this study, CSVd-free and CSVd-infected plants were prepared by culturing different-sized dissected shoot apical meristems (SAMs) of 'Piato'. Using these CSVd-free and CSVd-infected plants, we clarified the relationship between CSVd infection and the autonomous flowering of 'Piato'. Under natural short-day conditions, the flowering of plants regenerated from SAMs containing leaf primordia (LPs) was 1 month earlier than plants regenerated from LP-free SAMs. CSVd was detected from these early flowering plants by reverse transcription-polymerase chain reaction. On the other hand, CSVd was not detected in plants regenerated from LP-free SAMs. CSVd-infected and CSVd-free plants were grown under long-day conditions simulated by night-break lighting at 22:00 p.m. to 2:00 a.m. All CSVd-infected plants flowered autonomously even under long-day conditions; on the other hand, CSVd-free chrysanthemum plants maintained their vegetative growth. When the CSVd-free plants were inoculated with CSVd by grafting them to CSVd-infected rootstocks, they flowered autonomously even under night-break lighting. In this study, the results suggest that CSVd may control the qualitative development process, flowering, i.e. CSVd can induce the autonomous flowering of chrysanthemum.

Chrysanthemum↗

PubMed2005

In situ expression of the GmNMH7 gene is photoperiod-dependent in a unique soybean (Glycine max [L.] Merr.) flowering reversion system.

Soybean is a short-day plant and its flowering process can be reversed when switching from short-day to long-day conditions. Flowering reversion provides a useful system to study the flowering process in both forward and backward directions. In this study, we optimized a soybean flowering reversion system using a photoperiod-sensitive cultivar Zigongdongdou. Three types of terminal structures were found during flowering reversion: reversed terminal raceme (RTR), short terminal raceme (STR), and vegetative terminal (VT). The relative frequency of these terminal structures during flowering reversion under long day was dependent on the duration of the prior short day (SD) pretreatment. This process is phytochrome dependent and young plants were more susceptible to flowering reversion. Leaf removal increased the minimal SD period needed for the induction of STR. To demonstrate the application of this system, we studied the patterns of in situ expression of the GmNMH7 gene during flowering development and reversion. NMH7 family members encode MADS-box proteins and are unique in legume families since their expression can be detected in both developing flowers and nodules. In situ hybridization experiments using plants grown under different photoperiod cycles provided several lines of evidence supporting a close relationship between GmNMH7 gene expression and floral development in soybean. Furthermore, it seems that GmNMH7 may participate in flower development at different stages. Interestingly, the expression pattern of GmNMH7 in root nodules was also found to be regulated by photoperiod. These results support the notion that the photoperiod sensitive GmNMH7 gene may play multiple roles in growth and development in soybean.

Amino Acid Sequence↗

PubMed2003

Nectarless flowers: ecological correlates and evolutionary stability.

In animal-pollinated flowers, the pollinators cannot detect the presence of nectar before entering flowers, and therefore flowers may cheat by not producing nectar. An earlier model suggested that a mixed strategy of producing nectarful and nectarless flowers would be evolutionarily stable. Here we compare nectarless flowers as a cheating strategy with three competing hypotheses namely "visit-more-flowers", "cross-pollination enhancement" and "better contact". We collected field data on 28 species of plants to test some of the differential predictions of the hypotheses. Nectarless flowers were detected in 24 out of 28 plant species. Correlations of percent nectarless flowers with floral and ecological variables support the cheater flower hypothesis. We further model the cost-benefits of cheating and show that an evolutionary stable ratio of nectarless to nectarful flowers can be reached. The equilibrium ratio is mainly decided by factors associated with pollinator density and pollinator learning.

Animals↗

PubMed2006

Nonadditive effects of flower damage and hummingbird pollination on the fecundity of Mimulus luteus.

Flower herbivory and pollination have been described as interactive processes that influence each other in their effects on plant reproductive success. Few studies, however, have so far examined their joint effects in natural populations. In this paper we evaluate the influence of flower damage and pollination by the hummingbird Oreotrochilus leucopleurus on the fecundity of the Andean monkey flower Mimulus luteus. We performed a 2x2 factorial experiment, with artificial clipping of lower petals and selective exclusion of the hummingbird as main factors. In spite of the relatively low proportion (27.5%) of the variance in seed production accounted for by the full factorial model, artificial damage and hummingbird exclusion, as well as their interaction, were highly significant, indicating nonadditive effects of factors on plant fecundity. In the presence of hummingbirds, undamaged flowers had a seed production that was 1.7-fold higher than for damaged flowers, suggesting that the effect of flower damage on female reproductive success occurs probably as a consequence of hummingbird discrimination against damaged corollas. This result indicates that the impact of flower herbivory on plant fecundity was contingent on the presence or absence of hummingbirds, suggesting that pollinators may indirectly select for undamaged and probably resistant flower phenotypes. A second interaction effect revealed that undamaged flowers produced 78.5% more seeds in the absence of rather than in the presence of O. leucopleurus, raising the question of the ecological mechanism involved. We suggest that the strong territorial behavior exhibited by the bee Centris nigerrima may confine the foraging activities of the remaining bee species to safe sites within exclosures. Overall, our results provide evidence that hummingbird pollination and flower herbivory have interdependent effects on M. luteus fecundity, which indicates that it will be difficult to predict their ecological and evolutionary consequences unless interactions are analyzed in an integrated form.

Animals↗

PubMed2002

Ability of honeybee, Apis mellifera, to detect and discriminate odors of varieties of canola (Brassica rapa and Brassica napus) and snapdragon flowers (Antirrhinum majus).

Honeybees (Apis mellifera) use odors to identify and discriminate among flowers during foraging. This series of experiments examined the ability of bees to detect and discriminate among the floral odors of different varieties of two species of canola (Brassica rapa and Brassica napus) and also among three varieties of snapdragons (Antirhinnum majus). Individual worker honeybees were trained using a proboscis extension assay. The ability of bees to distinguish a floral odor from an air stimulus during training increased as the number of flowers used during training increased. Bees conditioned to the odor of one variety of flower were asked to discriminate it from the odors of other flowers in two different training assays. Bees were unable to discriminate among flowers at the level of variety in a randomized presentation of a reinforced floral odor and an unreinforced floral odor. In the second type of assay, bees were trained with one floral variety for 40 trials without reinforcement and then tested with the same variety or with other varieties and species. If a bee had been trained with a variety of canola, it was unable to differentiate the odor of one canola flower from the odor of other canola flowers, but it could differentiate canola from the odor of a snapdragon flower. Bees trained with the odor of snapdragon flowers readily differentiated the odor of one variety of a snapdragon from the odor of other varieties of snapdragons and also canola flowers. Our study suggests that both intensity and odor quality affect the ability of honeybees to differentiate among floral perfumes.

Animals↗

PubMed2003

AGL24 acts as a promoter of flowering in Arabidopsis and is positively regulated by vernalization.

MADS-domain-containing transcription factors comprise a large family of regulators that have diverse roles in plant development, including the regulation of flowering time. AGAMOUS-LIKE 20/SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) and FRUITFUL act to promote flowering, whereas FLOWERING LOCUS C (FLC), FLOWERING LOCUS M/MADS AFFECTING FLOWERING1, and SHORT VEGETATIVE PHASE are inhibitors of flowering. Here we report that AGAMOUS-LIKE 24 (AGL24) also plays a role in the regulation of flowering time. agl24 mutants are late flowering and overexpression of AGL24 causes early flowering in wild-type and late-flowering-mutant backgrounds. The effect of AGL24 overexpression is most pronounced in autonomous-pathway-mutant and FRIGIDA-containing backgrounds. The behavior of AGL24 is most similar to that of SOC1. Like SOC1, AGL24 mRNA levels are upregulated by vernalization. Unlike SOC1, however, AGL24 mRNA levels are not affected by FLC, and therefore AGL24 may represent an FLC-independent target of the vernalization pathway. There is also evidence for cross-talk between AGL24 and SOC1. When overexpressed, SOC1 and AGL24 are able to upregulate each other's expression. Thus, AGL24 represents another component in a network of MADS-domain-containing transcription factors that regulate flowering time.

Arabidopsis↗

PubMed2006

Evolution of funnel-revolver flowers and ornithophily in nasa (loasaceae).

Floral morphology, distribution, and flower visitors for 60 taxa of Nasa are investigated and compared to molecular trees inferred both from a combined marker analysis (ITS1 and trnL (UAA)) and from a single marker (ITS1). Flowers conform to two different floral types: Firstly, "tilt-revolver flowers", with spreading to reflexed, white to yellow petals and small, brightly coloured floral scales contrasting with the petals and firmly enclosing the nectar (Saccatae and Carunculatae); secondly, "funnel-revolver flowers", with half-erect to erect, orange to red petals and floral scales not contrasting with the petals, or enclosed in the corolla, and nectar freely accessible by funnel-shaped floral scales ( Alatae, Grandiflorae, and N. venezuelensis species group). Phylogenetic analysis shows that "tilt-revolver flowers" represent the plesiomorphic condition by outgroup comparison. The two groups with tilt-revolver flowers in Nasa are not monophyletic ( Saccatae are paraphyletic, Carunculatae are polyphyletic). Most Saccatae fall into two monophyletic assemblages, the N. poissoniana species group and the N. triphylla species group. The remainder of Saccatae group either with Grandiflorae ( N. insignis species group) or with Alatae ( N. laxa species group). The clades retrieved in the molecular analysis contradict the traditional classification, but are congruent with vegetative morphology, details of the flower morphology, and biogeography. "Funnel-revolver flowers" represent the derived condition, but molecular data suggest a convergent development (at least twice independently), since the corresponding species do not constitute a monophyletic group. "Tilt-revolver flowers" are visited and pollinated by bees (especially Colletidae), whereas "funnel-revolver flowers" are mostly visited by hummingbirds. The transition from melittophily to ornithophily may have been the license for the colonization of, and the diversification in, both cloud forest and high Andean habitats.

Animals↗

PubMed2002

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.

Flowers↗