Pelorism is the term, said to be first used by Charles Darwin, for the formation of 'peloric flowers' [1] which botanically is the abnormal production of radially symmetrical (actinomorphic) flowers in a species that usually produces bilaterally symmetrical (zygomorphic) flowers. [2] These flowers are spontaneous floral symmetry mutants. The term epanody is also applied to this phenomenon. [3] Bilaterally symmetrical (zygomorphic) flowers are known to have evolved several times from radially symmetrical (actinomorphic) flowers, these changes being linked to increasing specialisation in pollinators. [4]
Pelorism has been of interest since a five-spurred variety of the common toad-flax ( Linaria vulgaris L.) was first discovered in 1742 by a young Uppsala botanist on an island in the Stockholm archipelago and then in 1744 described by Carl Linnaeus. The mutant, spreading vegetatively, had five spurs rather than the usual one; however, the rest of the plant was normal. Linnaeus found that this variety was contrary to his concept that genera and species had universally arisen through an act of "original creation and remained unchanged since then". Linnaeus called this type of mutant a 'Peloria', the Greek for 'monster' or 'prodigy', because of the huge implications for the then current belief that species were immutable. He wrote that "This is certainly no less remarkable than if a cow were to give birth to a calf with a wolf's head." The peloric plant fascinated Linnaeus to the extent that he grew it at his summer residence in Hammarby and his explanation for it was that a toad-flax had been pollinated by another species. [5] Charles Darwin, Charles Victor Naudin, Johann Wolfgang von Goethe and Hugo de Vries amongst others analysed and wrote about this significant mutation. [6]
The botanist Thomas Fairchild corresponded with Carl Linnæus. Fairchild scientifically produced an artificial hybrid, Dianthus caryophyllus x barbatus in 1717 that became known as 'Fairchild's Mule', a cross between a Sweet william and a Carnation. [7] The production of hybrids further undermined the belief that species as created by God were immutable.
It is notable in foxgloves that the terminal flower more frequently develops peloric features than lateral flowers and this has had been put down to terminal buds having a greater supply of sap. [8] Charles Darwin took a particular interest in peloric flowers, growing and cross-pollinating Antirrhinums himself, as he saw the phenomenon as suggestive of a partial reversion to a past or ancestral type. [9] Peloric forms quite commonly appear as random mutations in several orchid species in nature and this is genetically controlled, although the expression can be influenced by both environmental changes and by stresses. The occurrence is unstable and the same plant may exhibit normally on the next flowering. [10]
In more highly evolved flowers such as orchids the details of pelorism may appear more complex with characteristics such as the two lateral petals replaced by two additional labella, the labellum replaced by an additional lateral petals in semipeloria or pseudopeloria where the modified labellum is less distinctively altered, however it is still distinguishable from the lateral petals and this confers a degree of zygomorphy upon the petal whorl. [11]
Although the production of peloric flowers has been shown to generally follow standard Mendelian inheritance, this is not fixed and had been linked to the inability of a plant to produce normal internodes, this failure resulting in the fusion of flower buds giving in actinomorphic flowers. [12] Foxglove plants show the terminal peloric bud flowering first followed by the more normal buds flowering below, the reverse of the normal flowering pattern, the terminal flowers withering first. [13] The CYCLOIDEA (CYC) gene controls floral symmetry and peloric antirrhinums have been artificially induced by this gene being knocking out. [14]
Peloria derives from both new Latin and from the Greek word pelōros, meaning 'monstrous'. [15]
Pelorism is found in several orchid species, such as Phalaenopsis it is demonstrated by flowers with abnormal numbers of petals or lips as a genetic trait, the expression of which is environmentally influenced and may appear random. It is widely noted in the mint family and species such as Digitalis purpurea , gloxinia, Antirrhinum majus , Pelargonium , and auricula. [16] Because peloric flowers are larger and arguably more attractive than normal flowers plants such as cultivars of the gloxinia (Sinningia speciosa) have been deliberately bred to have peloric flowers.
Ophrys apifera, known in Europe as the bee orchid, is a perennial herbaceous plant of the genus Ophrys, in the family of Orchidaceae. It serves as an example of sexually deceptive pollination and floral mimicry, a highly selective and highly evolved plant–pollinator relationship, and an example of fungal symbiosis,
Petals are modified leaves that surround the reproductive parts of flowers. They are often brightly colored or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the corolla. Petals are usually accompanied by another set of modified leaves called sepals, that collectively form the calyx and lie just beneath the corolla. The calyx and the corolla together make up the perianth, the non-reproductive portion of a flower. When the petals and sepals of a flower are difficult to distinguish, they are collectively called tepals. Examples of plants in which the term tepal is appropriate include genera such as Aloe and Tulipa. Conversely, genera such as Rosa and Phaseolus have well-distinguished sepals and petals. When the undifferentiated tepals resemble petals, they are referred to as "petaloid", as in petaloid monocots, orders of monocots with brightly colored tepals. Since they include Liliales, an alternative name is lilioid monocots.
Geraniaceae is a family of flowering plants placed in the order Geraniales. The family name is derived from the genus Geranium. The family includes both the genus Geranium and the garden plants called geraniums, which modern botany classifies as genus Pelargonium, along with other related genera.
Floral symmetry describes whether, and how, a flower, in particular its perianth, can be divided into two or more identical or mirror-image parts.
Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria. External symmetry can be easily seen by just looking at an organism. For example, the face of a human being has a plane of symmetry down its centre, or a pine cone displays a clear symmetrical spiral pattern. Internal features can also show symmetry, for example the tubes in the human body which are cylindrical and have several planes of symmetry.
Thelymitra, commonly known as sun orchids, is a genus of more than 100 species of plants in the orchid family, Orchidaceae. Unlike most other orchids, sun orchids lack a highly modified labellum and all three petals are similar in size, shape and colour. The column is, however, highly modified and usually has prominent wings or glands which are helpful in identifying the species. Most sun orchids close their flowers at night, in cloudy or cool weather, giving rise to their common name. The scientific name means "woman's hood" and refers to the hooded column present in most, but not all species. Most species are endemic to Australia although some are found as far from there as the Philippines and Indonesia. The type species, Thelymitra longifolia, the first to be formally described, was collected in New Zealand.
Sabiaceae is a family of flowering plants that were placed in the order Proteales according to the APG IV system. It comprises three genera, Meliosma, Ophiocaryon and Sabia, with 66 known species, native to tropical to warm temperate regions of southern Asia and the Americas. The family has also been called Meliosmaceae Endl., 1841, nom. rej.
A flower, also known as a bloom or blossom, is the reproductive structure found in flowering plants. Flowers consist of a combination of vegetative organs – sepals that enclose and protect the developing flower, petals that attract pollinators, and reproductive organs that produce gametophytes, which in flowering plants produce gametes. The male gametophytes, which produce sperm, are enclosed within pollen grains produced in the anthers. The female gametophytes are contained within the ovules produced in the carpels.
Antirrhinum majus, the common snapdragon, is a species of flowering plant belonging to the genus Antirrhinum. The plant was placed in the family Plantaginaceae following a revision of its prior classical family, Scrophulariaceae.
Pollination syndromes are suites of flower traits that have evolved in response to natural selection imposed by different pollen vectors, which can be abiotic or biotic, such as birds, bees, flies, and so forth through a process called pollinator-mediated selection. These traits include flower shape, size, colour, odour, reward type and amount, nectar composition, timing of flowering, etc. For example, tubular red flowers with copious nectar often attract birds; foul smelling flowers attract carrion flies or beetles, etc.
This page provides a glossary of plant morphology. Botanists and other biologists who study plant morphology use a number of different terms to classify and identify plant organs and parts that can be observed using no more than a handheld magnifying lens. This page provides help in understanding the numerous other pages describing plants by their various taxa. The accompanying page—Plant morphology—provides an overview of the science of the external form of plants. There is also an alphabetical list: Glossary of botanical terms. In contrast, this page deals with botanical terms in a systematic manner, with some illustrations, and organized by plant anatomy and function in plant physiology.
Hammarbya paludosa is a small orchid commonly known as bog orchid, bog adder's-mouth or bog adder's-mouth orchid. It grows in bogs in temperate and subarctic regions of the Northern Hemisphere.
Resupination is derived from the Latin word resupinus, meaning "bent back with the face upward" or "on the back". "Resupination" is the noun form of the adjective "resupine" which means "being upside-down, supine or facing upward".
Das entdeckte Geheimnis der Natur im Bau und in der Befruchtung der Blumen by Christian Konrad Sprengel was published in 1793, but received little acclaim during the author's lifetime. Sprengel's ideas were rejected by other naturalists when it was published, but the importance of this work was duly appreciated by Charles Darwin some sixty years later. Darwin's use of Sprengel's ideas and reference to this book in the seminal work on the Fertilisation of Orchids established Sprengel's book as one of the most important works in the fields of floral biology and pollination ecology and its author as a founding father of these fields.
Papilionaceous flowers are flowers with the characteristic irregular and butterfly-like corolla found in many, though not all, plants of the species-rich Faboideae subfamily of legumes. Tournefort suggested that the term Flores papilionacei originated with Valerius Cordus, who applied it to the flowers of the bean.
Lapeirousia is a genus in the plant family Iridaceae. It is endemic to sub-Saharan Africa, about a third of the species occurring in fynbos.
Floral biology is an area of ecological research that studies the evolutionary factors that have moulded the structures, behaviour and physiological aspects involved in the flowering of plants. The field is broad and interdisciplinary and involves research requiring expertise from multiple disciplines that can include botany, ethology, biochemistry, and entomology. A slightly narrower area of research within floral biology is sometimes called pollination biology or anthecology.
A nectar spur is a hollow extension of a part of a flower. The spur may arise from various parts of the flower: the sepals, petals, or hypanthium, and often contain tissues that secrete nectar (nectaries). Nectar spurs are present in many clades across the angiosperms, and are often cited as an example of convergent evolution.
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 often 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.
In botany, floral morphology is the study of the diversity of forms and structures presented by the flower, which, by definition, is a branch of limited growth that bears the modified leaves responsible for reproduction and protection of the gametes, called floral pieces.
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