Chasmogamy

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Chasmogamous (a) and cleistogamous (b) flowers of Viola pubescens. Arrows point to structure. Chasmogamy.jpg
Chasmogamous (a) and cleistogamous (b) flowers of Viola pubescens. Arrows point to structure.

Chasmogamy is the type of plant reproduction in which the flowers open up, enabling cross-pollination. This is in contrast to cleistogamy, in which the flowers stay closed and self-pollinate.

Chasmogamous flowers are commonly showy with open petals encircling exposed reproductive parts. Chasmogamous stems from Greek for "open marriage", named after the open arrangement of floral structures. [1] Once chasmogamous flowers have reached maturity, they unfurl and their stamens or style are made available for pollination. Although some plant species possess self-fertilizing chasmogamous flowers, most chasmogamous flowers are cross-pollinated by biotic (e.g. insects) or abiotic (e.g. wind) agents. [2]

Chasmogamous flowers that are cross-pollinated have the advantage of sexual reproduction between two different parents, resulting in sexual recombination and genetically distinct seeds. These distinct seeds increase genetic diversity of the plant population and reduce inbreeding depression and deleterious alleles. [2] Seeds produced by chasmogamous flowers that are cross-pollinated may also exhibit hybrid vigor (heterosis) and increased fitness.

To promote cross-pollination, chasmogamous flowers often have strikingly colored petals and nectar guides or nectaries to attract and reward pollinators. However, these attractive floral organs can be disadvantageous as they are energetically costly to produce and require a surplus of resources. [2] [3] Pollination of chasmogamous flowers is also dependent upon the availability of pollinating agents. Thus, chasmogamous flowers generally develop when resources like light, water, nutrients, and pollinators are high. [4]

In contrast to chasmogamous flowers are minute, bud-like cleistogamous ("closed marriage") flowers, and pollination of cleistogamous flowers is cleistogamy. Unlike chasmogamous flowers, cleistogamous flowers remain mechanically sealed throughout the entirety of their development and reproduction. The closed morphology of cleistogamous flowers hinders them from exposing their reproductive organs and forces self-pollination. Without the need for pollinating agents, cleistogamous flowers lack nectar and elaborate petals, making them much less costly to produce than chasmogamous flowers and developmentally favored in suboptimal conditions. [1] [5]

In addition to chasmogamy and cleistogamy, many plant species possess a mixed breeding system that utilizes both chasmogamous and cleistogamous flowers. This breeding system has been referred to under multiple names including true cleistogamy, [4] dimorphic cleistogamy, [1] and the chasmogamous/cleistogamous mixed breeding system. [2] In this mixed breeding system, species produce both chasmogamous and cleistogamous flowers on the same plant. Chasmogamous and cleistogamous flowers may exhibit spatial separation and develop simultaneously at different morphological locations, or the two flowers may be temporally separated and develop at different times during the flowering season. [6] Rarely, the two flowers have also been documented as being both spatially and temporally separated. [6] The presence of both flower types allows mixed breeding system species to cross-pollinate and self-fertilize. This leads to increases in genetic diversity and assures reproductive success in variable environmental and pollinator conditions. [2] [7]

See also

Related Research Articles

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<span class="mw-page-title-main">Nymphaeaceae</span> Family of plants

Nymphaeaceae is a family of flowering plants, commonly called water lilies. They live as rhizomatous aquatic herbs in temperate and tropical climates around the world. The family contains five genera with about 70 known species. Water lilies are rooted in soil in bodies of water, with leaves and flowers floating on or emergent from the surface. Leaves are round, with a radial notch in Nymphaea and Nuphar, but fully circular in Victoria and Euryale.

<span class="mw-page-title-main">Pollination</span> Biological process occurring in plants

Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, for example beetles; birds, butterflies, and bats; water; wind; and even plants themselves. Pollinating animals travel from plant to plant carrying pollen on their bodies in a vital interaction that allows the transfer of genetic material critical to the reproductive system of most flowering plants. When self-pollination occurs within a closed flower. Pollination often occurs within a species. When pollination occurs between species, it can produce hybrid offspring in nature and in plant breeding work.

<span class="mw-page-title-main">Self-pollination</span> Form of pollination

Self-pollination is a form of pollination in which pollen from the same plant arrives at the stigma of a flower or at the ovule. There are two types of self-pollination: in autogamy, pollen is transferred to the stigma of the same flower; in geitonogamy, pollen is transferred from the anther of one flower to the stigma of another flower on the same flowering plant, or from microsporangium to ovule within a single (monoecious) gymnosperm. Some plants have mechanisms that ensure autogamy, such as flowers that do not open (cleistogamy), or stamens that move to come into contact with the stigma. The term selfing that is often used as a synonym, is not limited to self-pollination, but also applies to other type of self-fertilization.

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<span class="mw-page-title-main">Sequential hermaphroditism</span> Sex change as part of the normal life cycle of a species

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<i>Viola pubescens</i> Species of flowering plant in the family Violaceae

Viola pubescens, commonly called the downy yellow violet, is a plant species of the genus Viola and is classified within the subsection Nudicaules of section Chamaemelanium. It is a widespread North American violet found in rich, mesic woodlands, and sometimes in meadows, from Minnesota and Ontario east to Nova Scotia and south to Virginia. V. pubescens produces two different types of flowers during the season, including chasmogamous flowers in the early spring and cleistogamous flowers summer through fall.

<i>Impatiens capensis</i> Species of flowering plant

Impatiens capensis, the orange jewelweed, common jewelweed, spotted jewelweed, jewelweed, spotted touch-me-not, or orange balsam, is an annual plant in the family Balsaminaceae that is native to North America. It is common in bottomland soils, ditches, and along creeks, often growing side by side with its less common relative, yellow jewelweed.

Plant reproduction is the production of new offspring in plants, which can be accomplished by sexual or asexual reproduction. Sexual reproduction produces offspring by the fusion of gametes, resulting in offspring genetically different from either parent. Asexual reproduction produces new individuals without the fusion of gametes, resulting in clonal plants that are genetically identical to the parent plant and each other, unless mutations occur.

<span class="mw-page-title-main">Cleistogamy</span> Self-pollination of non-opening flowers

Cleistogamy is a type of automatic self-pollination of certain plants that can propagate by using non-opening, self-pollinating flowers. Especially well known in peanuts, peas, and pansies, this behavior is most widespread in the grass family. However, the largest genus of cleistogamous plants is Viola.

<span class="mw-page-title-main">Nectar robbing</span> Foraging behavior

Nectar robbing is a foraging behavior utilized by some organisms that feed on floral nectar, carried out by feeding from holes bitten in flowers, rather than by entering through the flowers' natural openings. "Nectar robbers" usually feed in this way, avoiding contact with the floral reproductive structures, and therefore do not facilitate plant reproduction via pollination. Because many species that act as pollinators also act as nectar robbers, nectar robbing is considered to be a form of exploitation of plant-pollinator mutualism. While there is variation in the dependency on nectar for robber species, most species rob facultatively.

<span class="mw-page-title-main">Monocotyledon reproduction</span> Flowering plant reproduction system

The monocots are one of the two major groups of flowering plants, the other being the dicots. In order to reproduce they utilize various strategies such as employing forms of asexual reproduction, restricting which individuals they are sexually compatible with, or influencing how they are pollinated. Nearly all reproductive strategies that evolved in the dicots have independently evolved in monocots as well. Despite these similarities and their close relatedness, monocots and dicots have distinct traits in their reproductive biologies.

Sexual selection is described as natural selection arising through preference by one sex for certain characteristics in individuals of the other sex. Sexual selection is a common concept in animal evolution but, with plants, it is oftentimes overlooked because many plants are hermaphrodites. Flowering plants show many characteristics that are often sexually selected for. For example, flower symmetry, nectar production, floral structure, and inflorescences are just a few of the many secondary sex characteristics acted upon by sexual selection. Sexual dimorphisms and reproductive organs can also be affected by sexual selection in flowering plants.

<span class="mw-page-title-main">Mixed mating systems</span> Plants which reproduce in multiple ways

A mixed mating system, also known as “variable inbreeding” a characteristic of many hermaphroditic seed plants, where more than one means of mating is used. Mixed mating usually refers to the production of a mixture of self-fertilized (selfed) and outbred (outcrossed) seeds. Plant mating systems influence the distribution of genetic variation within and among populations, by affecting the propensity of individuals to self-fertilize or cross-fertilize . Mixed mating systems are generally characterized by the frequency of selfing vs. outcrossing, but may include the production of asexual seeds through agamospermy. The trade offs for each strategy depend on ecological conditions, pollinator abundance and herbivory and parasite load. Mating systems are not permanent within species; they can vary with environmental factors, and through domestication when plants are bred for commercial agriculture.

Reproductive assurance occurs as plants have mechanisms to assure full seed set through selfing when outcross pollen is limiting. It is assumed that self-pollination is beneficial, in spite of potential fitness costs, when there is insufficient pollinator services or outcross pollen from other individuals to accomplish full seed set.. This phenomenon has been observed since the 19th century, when Darwin observed that self-pollination was common in some plants. Constant pollen limitation may cause the evolution of automatic selfing, also known as autogamy. This occurs in plants such as weeds, and is a form of reproductive assurance. As plants pursue reproductive assurance through self-fertilization, there is an increase in homozygosity, and inbreeding depression, due to genetic load, which results in reduced fitness of selfed offspring. Solely outcrossing plants may not be successful colonizers of new regions due to lack of other plants to outcross with, so colonizing species are expected to have mechanisms of reproductive assurance - an idea first proposed by Herbert G. Baker and referred to as Baker's "law" or "rule". Baker's law predicts that reproductive assurance affects establishment of plants in many contexts, including spread by weedy plants and following long-distance dispersal, such as occurs during island colonization. As plants evolve towards increase self-fertilization, energy is redirected to seed production rather than characteristics that increased outcrossing, such as floral attractants, which is a condition known as the selfing syndrome.

References

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  6. 1 2 Jasieniuk, M.; Lechowicz, M. J. (1987). "Spatial and temporal variation in chasmogamy and cleistogamy in Oxalis montana (Oxalidaceae)" (PDF). American Journal of Botany. 74 (11): 1672–1680. doi:10.2307/2444136. JSTOR   2444136. Archived from the original (PDF) on 2016-03-08. Retrieved 2015-11-23.
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