Plant sexuality covers the wide variety of sexual reproduction systems found across the plant kingdom. This article describes morphological aspects of sexual reproduction of plants.
Among all living organisms, flowers, which are the reproductive structures of angiosperms, are the most varied physically and show the greatest diversity in methods of reproduction of all biological systems. Carolus Linnaeus (1735 and 1753) proposed a system of classification of flowering plants based on plant structures, since plants employ many different morphological adaptations involving sexual reproduction, flowers played an important role in that classification system. Later on Christian Konrad Sprengel (1793) studied plant sexuality and called it the "revealed secret of nature" and for the first time it was understood that the pollination process involved both biotic and abiotic interactions (Charles Darwin's theories of natural selection utilized this work to promote his idea of evolution). Plants that are not flowering plants (green alga, mosses, liverworts, hornworts, ferns and gymnosperms such as conifers) also have complex interplays between morphological adaptation and environmental factors in their sexual reproduction. The breeding system, or how the sperm from one plant fertilizes the ovum of another, is the single most important determinant of the mating structure of nonclonal plant populations. The mating structure or morphology of the flower parts and their arrangement on the plant in turn controls the amount and distribution of genetic variation, a central element in the evolutionary process.
Terminology
The flowers of angiosperms are determinate shoots that have sporophylls. The parts of flowers are named by scientists and show great variation in shape, these flower parts include sepals, petals, stamens and carpels. As a group the sepals form the calyx and as a group the petals form the corolla, together the corolla and the calyx is called the perianth. The stamens collectively are called the androecuim and the carpels collectively are called the gynoecium.
The complexity of the systems and devices used by plants to achieve sexual reproduction has resulted in botanists and evolutionary biologists using numerous terms to describe physical structures and functional strategies. Dellaporta and Calderon-Urrea (1993) list and define a variety of terms used to describe the modes of sexuality at different levels in flowering plants. This list is reproduced here, generalized to fit more than just plants that have flowers, and expanded to include other terms and more complete definitions.
Individual reproductive unit (a flower in angiosperms)
- Bisexual - or perfect flowers have both male (androecium) and female (gynoecium) reproductive structures, including stamens, carpels, and an ovary. Flowers that contain both androecium and gynoecium are called androgynous or hermaphroditic. Examples of plants with perfect or bisexual flowers include the lily, rose, and most plants with large showy flowers, though a perfect flower does not have to have petals or sepals. Other terms widely used are hermaphrodite , monoclinous , and synoecious . A complete flower is a perfect flower with petals and sepals.
- Unisexual - Reproductive structure that is either functionally male or functionally female. In angiosperms this condition is also called diclinous , imperfect or incomplete .
Individual plant sexuality
Many plants have complete flowers that have both male and female parts, others only have male or female parts and still other plants have flowers on the same plant that are a mix of male and female flowers. Some plants even have mixes that include all three types of flowers, where some flowers are only male, some are only female and some are both male and female. A distinction needs to be made between arrangements of sexual parts and the expression of sexuality in single plants versus the larger plant population. Some plants also undergo what is called Sex-switching , like Arisaema triphyllum which express sexual differences at different stages of growth. In some arums smaller plants produce all or mostly male flowers and as plants grow larger over the years the male flowers are replaced by more female flowers on the same plant. Arisaema triphyllum thus covers a multitude of sexual conditions in its life time; from nonsexual juvenile plants to young plants that are all male, as plants grow larger they have a mix of both male and female flowers, to large plants that have mostly female flowers. Other plant populations have plants that produce more male flowers early in the year and as plants bloom later in the growing season they produce more female flowers. In plants like Thalictrum dioicum all the plants in the species are either male or female.
Specific terms are used to describe the sexual expression of individual plants within a population.
- Hermaphrodite - A plant that has only bisexual reproductive units (flowers, conifer cones, or functionally equivalent structures). In angiosperm terminology a synonym is monoclinous from the Greek "one bed".
- Monoecious - an individual that has both male and female reproductive units (flowers, conifer cones, or functionally equivalent structures) on the same plant; from Greek for "one household". Individuals bearing separate flowers of both sexes at the same time are called simultaneously or synchronously monoecious. Individuals that bear flowers of one sex at one time are called consecutively monoecious; plants may first have single sexed flowers and then later have flowers of the other sex. Protoandrous describes individuals that function first as males and then change to females; protogynous describes individuals that function first as females and then change to males.
- Dioecious - refers to a plant population having separate male and female plants. That is, no individual plant of the population produces both microgametophytes (pollen) and megagametophytes (ovules); individual plants are either male or female. From Greek for "two households".
- Androecious - plants producing male flowers only, produce pollen but no seeds, the male plants of a dioecious population.
- Gynoecious - plants producing female flowers only, produces seeds but no pollen, the female of a dioecious population. In some plant populations, all individuals are gynoecious with non sexual reproduction used to produce the next generation.
- Subdioecious , a tendency in some dioecious populations to produce monoecious plants. The population produces normally male or female plants but some are hermaphroditic, with female plants producing some male or hermaphroditic flowers or vice versa. The condition is thought to represent a transition between hermaphroditism and dioecy..
- Gynomonoecious - has both hermaphrodite and female structures.
- Andromonoecious - has both hermaphrodite and male structures.
- Subandroecious - plant has mostly male flowers, with a few female or hermaphrodite flowers.
- Subgynoecious - plant has mostly female flowers, with a few male or hermaphrodite flowers.
- Polygamy - Plants with male, female and perfect (hermaphrodite) flowers on the same plant, called trimonoecious or polygamomonoecious plants, (see next section for use for plant populations). A polygamous inflorescence has both unisexual and bisexual flowers.
- Trimonoecious (polygamous) - male, female, and hermaphrodite floral morphs all appear on the same plant.
- Diclinous ("two beds"), an angiosperm term, includes all species with unisexual flowers, although particularly those with only unisexual flowers, i.e. the monoecious and dioecious species.
Plant population
Most often plants show uniform strategies across the species or in populations in their sexual expression and specific terms are used to describe the sexual expression of the population.
- Hermaphrodite - only hermaphrodite plants with flowers that have both male and female parts.
- Monoecious - only monoecious plants, that is plants have separate male and female flowers on the same plant. A plant population where the male and female organs are found in different flowers on the same plant. These plants are often wind pollinated. Examples of monoecious plants include corn, birch and pine trees, and most fig species.
- Dioecious - only dioecious plants, all plants are either female or male. The American Holly ( Ilex opaca ) is a famous example.
- Androdioecious - both male and h
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The Parts of A Perfect Flower
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Flower diagram
A COMPLETE ANGIOSPERM FLOWER FLOWER PARTS OCCUR IN WHORLS IN THE FOLLOWING ORDER- SEPALS, PETALS, STAMENS, PISTILS PEDICEL - flower stem RECEPTACLE - base of flower where other ...
Definition of complete flower
Definition as written by htop: A complete flower is a flower that has all four parts of the flower (sepals, petals, pistil, stamen) present.
complete flower - definition of complete flower by the Free Online ...
complete flower. A flower having all four floral parts: sepals, petals, stamens, and carpels. Compare incomplete flower. See also perfect flower.
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Flower Parts and Functions KS 2/3 T he parts of a simple flower. Complete the labels from the words below. W ithout plants all other living things could not exist.
complete flower definition of complete flower in the Free Online ...
complete flower [kəm′plēt ′flau̇·ər] (botany) A flower having all four floral parts, that is, having sepals, petals, stamens, and carpels.
The parts of a flower
The complete flower . A flower carries the sexual parts of plants. A complete flower has both male and female parts.
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complete flower ... of any other part that renders it incomplete (see photograph). A flower that lacks stamens is... in angiosperm (plant): General features) A complete ...