All flowering plants are heterosporous, producing two types of spores. Microspores are produced by meiosis inside anthers while megaspores are produced inside ovules, inside an ovary. In fact, anthers typically consist of four microsporangia and an ovule is an integumented megasporangium. Both types of spores develop into gametophytes inside sporangia. As with all heterosporous plants, the gametophytes also develop inside the spores (are endosporic). In the majority of species, individual flowers have both functional carpels and stamens. Botanists describe these flowers as being perfect or bisexual and the species as hermaphroditic.
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In a simple readings model, three gene activities interact in a combinatorial manner to determine the developmental identities of the organ primordia within the floral meristem. These gene functions are called a, b and C-gene functions. In the first floral whorl only a-genes are expressed, leading to the formation of sepals. In the second whorl both a- and B-genes are expressed, leading to the formation of petals. In the third whorl, b and C genes interact to form stamens and in the center of the flower C-genes alone give rise to carpels. The model is based upon studies of mutants in Arabidopsis thaliana and snapdragon, Antirrhinum majus. For example, when there is a loss of B-gene function, mutant flowers are produced with sepals in the first whorl as usual, but also in the second whorl instead of the normal petal formation. In the third whorl the lack of B function but presence of C-function mimics the fourth dissertation whorl, leading to the formation of carpels also in the third whorl. Most genes central in this model belong to the mads-box genes and are transcription factors that regulate the expression of the genes specific for each floral organ. Floral function see also: Plant reproductive morphology a "perfect flower this Crateva religiosa flower has both stamens (outer ring) and a pistil (center). The principal purpose of a flower is the reproduction of the individual and the species.
Florigen is produced in the leaves in reproductively favorable conditions and acts in buds and growing tips to induce a number of different physiological and morphological changes. 15 The first step of the transition is the transformation of the vegetative stem primordia into floral primordia. This occurs as biochemical changes take place to change cellular differentiation of leaf, bud and stem tissues into tissue that will grow into the reproductive organs. Growth of the central part of the stem tip stops or flattens out and the sides develop protuberances in a whorled or spiral fashion around the outside of the stem end. These protuberances develop into the sepals, petals, stamens, and carpels. Once this process begins, in most plants, it cannot be reversed and the stems develop flowers, even if the initial start of the flower formation event was essay dependent of some environmental cue. 16 Once the process begins, even if that cue is removed the stem will continue to develop a flower. Yvonne aitken has shown that flowering transition depends on a number of factors, and that plants flowering earliest under given conditions had the least dependence on climate whereas later-flowering varieties reacted strongly to the climate setup. Organ development main article: abc model of flower development The abc model of flower development The molecular control of floral organ identity determination appears to be fairly well understood in some species.
It has compressed internodes, bearing structures that in classical plant morphology are interpreted as highly modified leaves. 11 Detailed developmental studies, however, have shown that stamens are often initiated more or less like modified stems (caulomes) that in some cases may even resemble branchlets. 5 1 taking into account the whole diversity in the development of the androecium of flowering plants, we find a continuum between modified leaves (phyllomes modified stems (caulomes and modified branchlets (shoots). 12 13 Flowering transition The transition to report flowering is one of the major phase changes that a plant makes during its life cycle. The transition must take place at a time that is favorable for fertilization and the formation of seeds, hence ensuring maximal reproductive success. To meet these needs a plant is able to interpret important endogenous and environmental cues such as changes in levels of plant hormones and seasonable temperature and photoperiod changes. 14 Many perennial and most biennial plants require vernalization to flower. The molecular interpretation of these signals is through the transmission of a complex signal known as florigen, which involves a variety of genes, including constans, flowering locus c and flowering locus.
It can represent a taxon, usually giving ranges of the numbers of different organs, or particular species. Floral formulae have been developed in the early 19th century and their use has declined since. (2010) devised an extension of the existing model to broaden the descriptive capability of the formula. 6 The format of floral formulae differs in different parts of the world, yet they convey the same information. The structure of a flower can also be expressed by the means of floral diagrams. The use of schematic diagrams can replace long descriptions or complicated drawings as a tool for understanding both floral structure and evolution. Such diagrams may show important features of flowers, including the relative positions of the various organs, including the presence of fusion and symmetry, as well as structural details. 7 development A flower develops on a modified shoot or axis from a determinate apical meristem ( determinate meaning the axis grows to a set size).
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The stem or stalk subtending a flower is called a peduncle. If a peduncle supports more than one flower, the stems connecting each flower to the main axis are called pedicels. The apex of a flowering stem forms a terminal swelling which is called the torus or receptacle. Inflorescence The familiar calla lily is not a single flower. It is actually an inflorescence of tiny flowers pressed together on a central stalk that is surrounded by a large petal-like bract. Main article: Inflorescence In those species that have more than one flower on an axis, the collective cluster of flowers is termed an inflorescence.
Some inflorescences are composed of many small flowers arranged assam in a formation that resembles a single flower. The common example of this is most members of the very large composite (Asteraceae) group. A single daisy or sunflower, for example, is not a flower but a flower head —an inflorescence composed of numerous flowers (or florets). An inflorescence may include specialized stems and modified leaves known as bracts. Floral diagrams and floral formulae main articles: Floral formula and Floral diagram A floral formula is a way to represent the structure of a flower using specific letters, numbers and symbols, presenting substantial information about the flower in a compact form.
When petals are fused into a tube or ring that falls away as a single unit, they are sympetalous (also called gamopetalous ). Connate petals may have distinctive regions: the cylindrical base is the tube, the expanding region is the throat and the flaring outer region is the limb. A sympetalous flower, with bilateral symmetry with an upper and lower lip, is bilabiate. Flowers with connate petals or sepals may have various shaped corolla or calyx, including campanulate, funnelform, tubular, urceolate, salverform or rotate. Referring to "fusion as it is commonly done, appears questionable because at least some of the processes involved may be non-fusion processes. For example, the addition of intercalary growth at or below the base of the primordia of floral appendages such as sepals, petals, stamens and carpels may lead to a common base that is not the result of fusion.
3 4 5 Left: A normal zygomorphic Streptocarpus flower. Right: An aberrant peloric Streptocarpus flower. Both of these flowers appeared on the Streptocarpus hybrid 'Anderson's Crows' wings'. Many flowers have a symmetry. When the perianth is bisected through the central axis from any point and symmetrical halves are produced, the flower is said to be actinomorphic or regular,. This is an example of radial symmetry. When flowers are bisected and produce only one line that produces symmetrical halves, the flower is said to be irregular or zygomorphic,. Snapdragon or most orchids. Flowers may be directly attached to the plant at their base (sessile—the supporting stalk or stem is highly reduced or absent).
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1 These modifications have significance in brief the evolution of flowering plants and are used extensively by botanists to establish relationships among plant species. The four main parts of a flower are generally defined by their positions on the receptacle and not by their function. Many flowers lack some parts or parts may be modified into other functions and/or look like what is typically another part. In some families, like ranunculaceae, the petals are greatly reduced and in many species the sepals are colorful and petal-like. Other flowers have modified stamens lab that are petal-like; the double flowers of peonies and Roses are mostly petaloid stamens. 2 Flowers show great variation and plant scientists describe this variation in a systematic way to identify and distinguish species. Specific terminology is used to describe flowers and their parts. Many flower parts are fused together; fused parts originating from the same whorl are connate, while fused parts originating from different whorls are adnate ; parts that are not fused are free.
These give rise to egg cells. The gynoecium of a flower is also described using an alternative terminology wherein the orders structure one sees in the innermost whorl (consisting of an ovary, style and stigma) is called a pistil. A pistil may consist of a single carpel or a number of carpels fused together. The sticky tip of the pistil, the stigma, is the receptor of pollen. The supportive stalk, the style, becomes the pathway for pollen tubes to grow from pollen grains adhering to the stigma. The relationship to the gynoecium on the receptacle is described as hypogynous (beneath a superior ovary perigynous (surrounding a superior ovary or epigynous (above inferior ovary). Structure Although the arrangement described above is considered "typical plant species show a wide variation in floral structure.
Corolla (flower) Collectively the calyx and corolla form the perianth (see diagram). Calyx : the outermost whorl consisting of units called sepals ; these are typically green and enclose the rest of the flower in the bud stage, however, they can be absent or prominent and petal-like in some species. Corolla : the next whorl toward the apex, composed of units called petals, which are typically thin, soft and colored to attract animals that help the process of pollination. Reproductive main articles: Plant reproductive morphology, androecium, and Gynoecium Reproductive parts of Easter Lily ( Lilium longiflorum ). Petal Androecium (from Greek andros oikia : man's house the next whorl (sometimes multiplied into several whorls consisting of units called stamens. Stamens consist of two parts: a stalk called a filament, topped by an anther where pollen is produced by meiosis and eventually dispersed. Gynoecium (from Greek gynaikos oikia : woman's house the innermost whorl of a flower, consisting of one or more units called carpels. The carpel or multiple fused carpels form a hollow structure called an ovary, which produces ovules internally. Ovules are megasporangia and they in turn produce megaspores by meiosis which develop into female gametophytes.
Flowers contain sporangia and are the site where gametophytes develop. Many flowers have evolved to be attractive to animals, so as to cause them to be vectors for the transfer teresa of pollen. After fertilization, the ovary of the flower develops into fruit containing seeds. In addition to facilitating the reproduction of flowering plants, flowers have long been admired and used by humans to bring beauty to their environment, and also as objects of romance, ritual, religion, medicine and as a source of food. Contents, morphology, diagram of flower parts. The essential parts of a flower can be considered in two parts: the vegetative part, consisting of petals and associated structures in the perianth, and the reproductive or sexual parts. A stereotypical flower consists of four kinds of structures attached to the tip of a short stalk.
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For other uses, see, flower (disambiguation). For business other uses, see, floral (disambiguation). A poster with flowers or clusters of flowers produced by twelve species of flowering plants from different families. A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division, magnoliophyta, also called angiosperms). The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs. Flowers may facilitate outcrossing (fusion of sperm and eggs from different individuals in a population) or allow selfing (fusion of sperm and egg from the same flower). Some flowers produce diaspores without fertilization ( parthenocarpy ).