Pollen is a fine to coarse powdery substance comprising pollen grains which are male microgametophytes of seed plants, which produce male gametes. Pollen grains have a hard coat made of sporopollenin that protects the gametophytes during the process of their movement from the stamens to the pistil of flowering plants, or from the male cone to the female cone of coniferous plants. If pollen lands on a compatible pistil or female cone, it germinates, producing a pollen tube that transfers the sperm to the ovule containing the female gametophyte. Individual pollen grains are small enough to require magnification to see detail; the study of pollen is called palynology and is useful in paleoecology, paleontology and forensics. Pollen in plants is used for transferring haploid male genetic material from the anther of a single flower to the stigma of another in cross-pollination. In a case of self-pollination, this process takes place from the anther of a flower to the stigma of the same flower. Pollen is used as food and food supplement.
However, because of agricultural practices, it is contaminated by agricultural pesticides. Pollen itself is not the male gamete; each pollen grain contains a generative cell. In flowering plants the vegetative tube cell produces the pollen tube, the generative cell divides to form the two sperm cells. Pollen is produced in the microsporangia in the male cone of a conifer or other gymnosperm or in the anthers of an angiosperm flower. Pollen grains come in a wide variety of shapes and surface markings characteristic of the species. Pollen grains of pines and spruces are winged; the smallest pollen grain, that of the forget-me-not, is around 6 µm in diameter. Wind-borne pollen grains can be as large as about 90–100 µm. In angiosperms, during flower development the anther is composed of a mass of cells that appear undifferentiated, except for a differentiated dermis; as the flower develops, four groups of sporogenous cells form within the anther. The fertile sporogenous cells are surrounded by layers of sterile cells that grow into the wall of the pollen sac.
Some of the cells grow into nutritive cells that supply nutrition for the microspores that form by meiotic division from the sporogenous cells. In a process called microsporogenesis, four haploid microspores are produced from each diploid sporogenous cell, after meiotic division. After the formation of the four microspores, which are contained by callose walls, the development of the pollen grain walls begins; the callose wall is broken down by an enzyme called callase and the freed pollen grains grow in size and develop their characteristic shape and form a resistant outer wall called the exine and an inner wall called the intine. The exine is. Two basic types of microsporogenesis are recognised and successive. In simultaneous microsporogenesis meiotic steps I and II are completed prior to cytokinesis, whereas in successive microsporogenesis cytokinesis follows. While there may be a continuum with intermediate forms, the type of microsporogenesis has systematic significance; the predominant form amongst the monocots is successive.
During microgametogenesis, the unicellular microspores undergo mitosis and develop into mature microgametophytes containing the gametes. In some flowering plants, germination of the pollen grain may begin before it leaves the microsporangium, with the generative cell forming the two sperm cells. Except in the case of some submerged aquatic plants, the mature pollen grain has a double wall; the vegetative and generative cells are surrounded by a thin delicate wall of unaltered cellulose called the endospore or intine, a tough resistant outer cuticularized wall composed of sporopollenin called the exospore or exine. The exine bears spines or warts, or is variously sculptured, the character of the markings is of value for identifying genus, species, or cultivar or individual; the spines may be less than a micron in length referred to as spinulose, or longer than a micron referred to as echinate. Various terms describe the sculpturing such as reticulate, a net like appearance consisting of elements separated from each other by a lumen.
The pollen wall protects the sperm. The pollen grain surface is covered with waxes and proteins, which are held in place by structures called sculpture elements on the surface of the grain; the outer pollen wall, which prevents the pollen grain from shrinking and crushing the genetic material during desiccation, is composed of two layers. These two layers are the tectum and the foot layer, just above the intine; the tectum and foot layer are separated by a region called the columella, composed of strengthening rods. The outer wall is constructed with a resistant biopolymer called sporopollenin. Pollen apertures are regions of the pollen wall that may involve exine thinning or a significant reduction in exine thickness, they allow shrinking and swelling of the grain caused by changes in moisture content. Elongated apertures or furrows in the pollen grain are called sulci. Apertures that are more circular are called pores. Colpi and pores are major features in the identification of classes of pollen.
Pollen may be referre
In scientific nomenclature, a synonym is a scientific name that applies to a taxon that goes by a different scientific name, although the term is used somewhat differently in the zoological code of nomenclature. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies; this name is no longer in use: it is now a synonym of the current scientific name, Picea abies. Unlike synonyms in other contexts, in taxonomy a synonym is not interchangeable with the name of which it is a synonym. In taxonomy, synonyms have a different status. For any taxon with a particular circumscription and rank, only one scientific name is considered to be the correct one at any given time. A synonym cannot exist in isolation: it is always an alternative to a different scientific name. Given that the correct name of a taxon depends on the taxonomic viewpoint used a name, one taxonomist's synonym may be another taxonomist's correct name. Synonyms may arise whenever the same taxon is named more than once, independently.
They may arise when existing taxa are changed, as when two taxa are joined to become one, a species is moved to a different genus, a variety is moved to a different species, etc. Synonyms come about when the codes of nomenclature change, so that older names are no longer acceptable. To the general user of scientific names, in fields such as agriculture, ecology, general science, etc. A synonym is a name, used as the correct scientific name but, displaced by another scientific name, now regarded as correct, thus Oxford Dictionaries Online defines the term as "a taxonomic name which has the same application as another one, superseded and is no longer valid." In handbooks and general texts, it is useful to have synonyms mentioned as such after the current scientific name, so as to avoid confusion. For example, if the much advertised name change should go through and the scientific name of the fruit fly were changed to Sophophora melanogaster, it would be helpful if any mention of this name was accompanied by "".
Synonyms used in this way may not always meet the strict definitions of the term "synonym" in the formal rules of nomenclature which govern scientific names. Changes of scientific name have two causes: they may be taxonomic or nomenclatural. A name change may be caused by changes in the circumscription, position or rank of a taxon, representing a change in taxonomic, scientific insight. A name change may be due to purely nomenclatural reasons, that is, based on the rules of nomenclature. Speaking in general, name changes for nomenclatural reasons have become less frequent over time as the rules of nomenclature allow for names to be conserved, so as to promote stability of scientific names. In zoological nomenclature, codified in the International Code of Zoological Nomenclature, synonyms are different scientific names of the same taxonomic rank that pertain to that same taxon. For example, a particular species could, over time, have had two or more species-rank names published for it, while the same is applicable at higher ranks such as genera, orders, etc.
In each case, the earliest published name is called the senior synonym, while the name is the junior synonym. In the case where two names for the same taxon have been published the valid name is selected accorded to the principle of the first reviser such that, for example, of the names Strix scandiaca and Strix noctua, both published by Linnaeus in the same work at the same date for the taxon now determined to be the snowy owl, the epithet scandiaca has been selected as the valid name, with noctua becoming the junior synonym. One basic principle of zoological nomenclature is that the earliest published name, the senior synonym, by default takes precedence in naming rights and therefore, unless other restrictions interfere, must be used for the taxon. However, junior synonyms are still important to document, because if the earliest name cannot be used the next available junior synonym must be used for the taxon. For other purposes, if a researcher is interested in consulting or compiling all known information regarding a taxon, some of this may well have been published under names now regarded as outdated and so it is again useful to know a list of historic synonyms which may have been used for a given current taxon name.
Objective synonyms refer to taxa with same rank. This may be species-group taxa of the same rank with the same type specimen, genus-group taxa of the same rank with the same type species or if their type species are themselves objective synonyms, of family-group taxa with the same type genus, etc. In the case of subjective synonyms, there is no such shared type, so the synonymy is open to taxonomic judgement, meaning that th
Maxillarieae is a large and complex tribe of orchids native to South and Central America. Within the tribe there are eight subtribes one of, that of the genus Maxillaria. Tribe Maxillarieae contains 70 to 80 genera with about 1,000 species. Most show pseudobulbs. Blooms have four pollinia. Subtribe Corallorhizinae: all epiparasites. Genera: Aplectrum, Corallorrhiza Subtribe Zygopetalinae: about 150 species. Most exhibited hybrids are to be found in this subtribe. Alliance Warrea Genera: Otostylis, Warrea Alliance Zygopetalum Genera: Acacallis, Batemannia, Cheiradenia, Cochleanthes, Pabstia, Zygopetalum Alliance Bollea Genera: Bollea, Cochleanthes, Kefersteinia, Stenia Alliance Vargasiella Genera: Vargasiella Unallied Genera within Zygopetalinae Genera: Benzingia, Chaubardiella, Galeottia, Koellensteinia, Paradisanthus, Warreella, Zygosepalum Alliance Hybrids Genera: Aitkenara, Bollopetalum, Cochella, Cochlenia, Durutyara, Huntleanthes, Keferanthes, Otocolax, Palmerara, Zygocaste, Zygonisia, Zygostylis Subtribe Bifrenariinae: thin and pleated leaves.
Genera: Bifrenaria, Xylobium Subtribe Lycastinae: thin and pleated leaves. Genera: Anguloa, Lycaste, Rudolfiella, Sudamerlycaste Teuscheria, Xylobium Subtribe Stanhopeinae: Genera: Acineta, Braemia, Coryanthes, Gongora, Houlletia, Kegeliella, Lueddemannia, Polycycnis, Sievekingia, Stanhopea, Vasqueziella Subtribe Coeliopsidinae: Genera: Coeliopsis, Peristeria Subtribe Maxillariinae: largest subtribe with nearly half of the tribe species; the leathery leaves are conduplicate, i.e. folded together lengthwise. Genera: Chrysocycnis, Maxillaria, Pityphyllum, Sepalosaccus, Trigonidium Subtribe Dichaeinae Genera: Dichaea Subtribe Telipogoninae Genera: Telipogon, Trichoceros Subtribe Ornithocephalinae Genera: Ornithocephalus, Zygostates W. Mark Whitten, Norris H. Williams and Mark W. Chase. "Subtribal and generic relationships of Maxillarieae with emphasis on Stanhopeinae: combined molecular evidence". American Journal of Botany. American Journal of Botany, Vol. 87, No. 12. 87: 1842–1856. Doi:10.2307/2656837.
JSTOR 2656837. PMID 11118422. - on line here
A pollinium is a coherent mass of pollen grains in a plant that are the product of only one anther, but are transferred, during pollination, as a single unit. This is seen in plants such as orchids and many species of milkweeds. Usage of the term differs: in some orchids two masses of pollen are well attached to one another, but in other orchids there are two halves each of, sometimes referred to as a pollinium. Most orchids have waxy pollinia; these are connected to one or two elongate stipes, which in turn are attached to a sticky viscidium, a disc-shaped structure that sticks to a visiting insect. Some orchid genera have mealy pollinia; these are tapering into a caudicle, attached to the viscidium. They extend into the middle section of the column; the pollinarium is a collective term that means either the complete set of pollinia from all the anthers of a flower, as in Asclepiadoideae, in Asclepiadoideae, a pair of pollinia and the parts that connect them, or in orchids, a pair of pollinia with two viscidia and the other connecting parts
In botany, a stipe is a stalk that supports some other structure. The precise meaning is different depending on. In the case of ferns, the stipe is only the petiole from the rootstock to the beginning of the leaf tissue, or lamina; the continuation of the structure within the lamina is termed a rachis. In flowering plants, the term is used in reference to a stalk that sometimes supports a flower's ovary. In orchids, the stipe or caudicle is the stalk-like support of the pollinia, it is a non-viscid strap connecting the pollinia with the viscidium. A stipe is a structure found in organisms that are studied by botanists but that are no longer classified as plants, it may be the stem-like part of the thallus of a mushroom or a seaweed, is common among brown algae such as kelp. The stipe of a kelp contains a central region of cells that, like the phloem of vascular plants, serves to transport nutrients within the alga. Rachis Stipe, the stalk supporting the fruiting body of some fungi
The column, or technically the gynostemium, is a reproductive structure that can be found in several plant families: Aristolochiaceae and Stylidiaceae. It is derived from the fusion of both male and female parts into a single organ; this means that the style and stigma of the pistil, with the filaments and one or more anthers, are all united. The stigma is pointing downwards after resupination; this stigma has the form of a small bowl, the clinandrium, a viscous surface embedding the single anther. On top of it all is the anther cap. Sometimes there is a small extension or little beak to the median stigma lobe, called rostellum. Column wings may project laterally from the stigma; the column foot is formed by the attachment of the lip to the basal protruding part of the column. One speaks of a mentum if the lateral sepals are basally adnate; the column both releases pollen and receives it for fertilization. In the Orchidaceae family, unlike all other flowering plants, the single male anther at the tip of the column produces pollen, not free and powdery but held in waxy masses of two, four or six pellets called pollinia.
The transfer of pollinia from one flower to another, though efficient, is reliant upon one particular species of arthropods and it can be catastrophic for the population if its pollinator disappears from the community
The Vandeae is a large monophyletic tribe within the family of orchids. This tribe contains 1,700 - 2,000 species in more than 150 genera; the classification of taxa within this tribe is still based on floral morphology. Only a few attempts have been made to obtain a classification based on molecular evidence based on sequence data from several plastid-encoded DNA regions; these orchids are pantropical epiphytes and occur in tropical Asia, the Pacific Islands and Africa. Many of these orchids are horticulturally important Vanda and Phalaenopsis; this tribe is subdivided into four subtribes: Subtribe Aeridinae: largest subtribe with more than 1,000 species in 103 genera, including about 200 hybrid species. They are distinguished from the other subtribes by having an entire rostellum, a small spur formed by the lip, four pollinia. Subtribe Aerangidinae: about 300 species in 36 genera, they are distributed through tropical Madagascar. They are distinguished from the other subtribes by having an elongate rostellum, an elongate spur, two pollinia.
Subtribe Angraecinae: about 400 species in 19 genera. They occur in tropical Africa, the Mascarene and Comoros Islands and two genera in tropical America, they are distinguished from the other subtribes by having an apron-like rostellum, an elongate spur, two pollinia. Subtribe Polystachyinae: about 220 species in four genera: Hederorkis, Imerinaea and Polystachya They all show four pollinia; the lip has mealy hairs called pseudopollen on the upper surface. Taxonomy of the Orchidaceae Cameron et al. A Phylogenetic Analysis of the Orchidaceae: Evidence from rbcL Nucleotide Sequences, American Journal of Botany 86: 208-224 Barbara S. Carlsward, W. Mark Whitten, Norris H. Williams2and Benny Bytebier. "Molecular phylogenetics of Vandeae and the evolution of leaflessness". American Journal of Botany. 93: 770–786. Doi:10.3732/ajb.93.5.770. PMID 21642140. CS1 maint: Multiple names: authors list