Flies are insects with a pair of functional wings for flight and a pair of vestigial hindwings called halteres for balance. They are classified as an order called Diptera, that name being derived from the Greek δι- di- "two", πτερόν pteron "wings"; the order Diptera is divided with about 110 families divided between them. The earliest fly fossils found so far are from the Triassic, about 240 million years ago. Many insects, such as the butterfly, contain the word are not Dipterans; the word "fly" is sometimes used colloquially and non-scientifically as a name for any small flying insect: the term "true fly" is sometimes invoked to make clear the insect being referenced is a Dipteran. Flies have a mobile head, with a pair of large compound eyes, mouthparts designed for piercing and sucking, or for lapping and sucking in the other groups; the suborder Nematocera have long antennae. Flies have only a single pair of wings to fly; the hindwings evolved into advanced mechanosensory organs, which act as high-speed sensors of rotational movement and allow them to perform advanced aerobatics.
Claws and pads on their feet enable them to cling to smooth surfaces. The life cycle of flies consists of the eggs, larva and the adult. Flies undergo complete metamorphosis; the pupa in higher dipterans is a tough capsule. Flies have short lives: for example, the adult housefly lives about a month; the source of nutrition for adult flies is liquified food, including nectar. Flies are of human importance, they are important pollinators, second only to their Hymenopteran relatives. They may have been responsible for the first plant pollination in the Triassic. Mosquitoes are vectors for malaria, West Nile fever, yellow fever and other infectious diseases. Flies can be annoyances in some parts of the world where they can occur in large numbers and settling on the skin or eyes to bite or seek fluids. Larger flies such as tsetse flies and screwworms cause significant economic harm to cattle. Blowfly larvae, known as gentles, other dipteran larvae, known more as maggots, are used as fishing bait, as food for carnivorous animals, in medicine for debridement to clean wounds.
Fruit flies are used as model organisms in research. In culture, the subject of flies appears in religion, literature and music. Dipterans are insects that undergo radical metamorphosis, they belong to the Mecopterida, alongside the Mecoptera, Siphonaptera and Trichoptera. The possession of a single pair of wings distinguishes most true flies from other insects with "fly" in their names. However, some true flies such as Hippoboscidae have become secondarily wingless; the cladogram represents the current consensus view. The first true dipterans known are from the Middle Triassic around 240 million years ago, they became widespread during the Middle and Late Triassic. Phylogenetic analysis of times of divergence suggests that dipterans originated in the Permian, some 260 million years ago. Modern flowering plants did not appear until the Cretaceous, so the original dipterans must have had a different source of nutrition other than nectar. Based on the attraction of many modern fly groups to shiny droplets, it has been suggested that they may have fed on honeydew produced by sap-sucking bugs which were abundant at the time, dipteran mouthparts are well-adapted to softening and lapping up the crusted residues.
The basal clades in the Diptera include the enigmatic Nymphomyiidae. Three episodes of evolutionary radiation are thought to have occurred based on the fossil record. Many new species of lower Diptera developed in the Triassic, about 220 million years ago. Many lower Brachycera appeared in the Jurassic, some 180 million years ago. A third radiation took place among the Schizophora at the start of the Paleogene, 66 million years ago; the phylogenetic position of Diptera has been controversial. The monophyly of holometabolous insects has long been accepted, with the main orders being established as Lepidoptera, Coleoptera and Diptera, it is the relationships between these groups which has caused difficulties. Diptera is thought to be a member of Mecopterida, along with Lepidoptera, Siphonaptera and Strepsiptera. Diptera has been grouped with Siphonaptera and Mecoptera in the Antliophora, but this has not been confirmed by molecular studies. Diptera were traditionally broken down into two suborders and Brachycera, distinguished by the differences in antennae.
The Nematocera are recognized by their elongated bodies and many-segmented feathery antennae as represented by mosquitoes and crane flies. The Brachycera have rounder bodies and much sh
A cotyledon is a significant part of the embryo within the seed of a plant, is defined as "the embryonic leaf in seed-bearing plants, one or more of which are the first leaves to appear from a germinating seed." The number of cotyledons present is one characteristic used by botanists to classify the flowering plants. Species with one cotyledon are called monocotyledonous. Plants with two embryonic leaves are termed dicotyledonous. In the case of dicot seedlings whose cotyledons are photosynthetic, the cotyledons are functionally similar to leaves. However, true leaves and cotyledons are developmentally distinct. Cotyledons are formed during embryogenesis, along with the root and shoot meristems, are therefore present in the seed prior to germination. True leaves, are formed post-embryonically from the shoot apical meristem, responsible for generating subsequent aerial portions of the plant; the cotyledon of grasses and many other monocotyledons is a modified leaf composed of a scutellum and a coleoptile.
The scutellum is a tissue within the seed, specialized to absorb stored food from the adjacent endosperm. The coleoptile is a protective cap. Gymnosperm seedlings have cotyledons, these are variable in number, with from 2 to 24 cotyledons forming a whorl at the top of the hypocotyl surrounding the plumule. Within each species, there is still some variation in cotyledon numbers, e.g. Monterey pine seedlings have 5–9, Jeffrey pine 7–13, but other species are more fixed, with e.g. Mediterranean cypress always having just two cotyledons; the highest number reported is for big-cone pinyon, with 24. The cotyledons may be ephemeral, lasting only days after emergence, or persistent, enduring at least a year on the plant; the cotyledons contain the stored food reserves of the seed. As these reserves are used up, the cotyledons may turn green and begin photosynthesis, or may wither as the first true leaves take over food production for the seedling. Cotyledons may be either epigeal, expanding on the germination of the seed, throwing off the seed shell, rising above the ground, becoming photosynthetic.
The latter is the case where the cotyledons act as a storage organ, as in many nuts and acorns. Hypogeal plants have larger seeds than epigeal ones, they are capable of surviving if the seedling is clipped off, as meristem buds remain underground. The tradeoff is whether the plant should produce a large number of small seeds, or a smaller number of seeds which are more to survive. Related plants show a mixture of hypogeal and epigeal development within the same plant family. Groups which contain both hypogeal and epigeal species include, for example, the Araucariaceae family of Southern Hemisphere conifers, the Fabaceae, the genus Lilium; the garden grown common bean - Phaseolus vulgaris - is epigeal while the related runner bean - Phaseolus coccineus - is hypogeal. The term cotyledon was coined by Marcello Malpighi. John Ray was the first botanist to recognize that some plants have two and others only one, the first to recognize the immense importance of this fact to systematics, in Methodus plantarum.
Theophrastus and Albertus Magnus may have recognized the distinction between the dicotyledons and monocotyledons. Tiscali.reference - Cotyledon
Gnetophyta is a division of plants, grouped within the gymnosperms, that consists of some 70 species across the three relict genera: Gnetum and Ephedra. Fossilized pollen attributed to a close relative of Ephedra has been dated as far back as the Early Cretaceous. Though diverse and dominant in the Paleogene and the Neogene, only three families, each containing a single genus, are still alive today; the primary difference between gnetophytes and other gymnosperms is the presence of vessel elements, a system of conduits that transport water within the plant, similar to those found in flowering plants. Because of this, gnetophytes were once thought to be the closest gymnosperm relatives to flowering plants, but more recent molecular studies have brought this hypothesis into question. Though it is clear they are all related, the exact evolutionary inter-relationships between gnetophytes are unclear; some classifications hold that all three genera should be placed in a single order, while other classifications say they should be distributed among three separate orders, each containing a single family and genus.
Most morphological and molecular studies confirm that the genera Gnetum and Welwitschia diverged from each other more than they did from Ephedra. Unlike most biological groupings, it is difficult to find many common characteristics between all of the members of the gnetophytes; the two common characteristics most used are the presence of enveloping bracts around both the ovules and microsporangia as well as a micropylar projection of the outer membrane of the ovule that produces a pollination droplet, though these are specific compared to the similarities between most other plant divisions. L. M. Bowe refers to the gnetophyte genera as a "bizarre and enigmatic" trio because, the gnetophytes' specialization to their respective environments is so complete that they hardly resemble each other at all. Gnetum species are woody vines in tropical forests, though the best-known member of this group, Gnetum gnemon, is a tree native to western Malesia; the one remaining species of Welwitschia, Welwitschia mirabilis, native only to the dry deserts of Namibia and Angola, is a ground-hugging species with only two large strap-like leaves that grow continuously from the base throughout the plant's life.
Ephedra species, known as "jointfirs" in the United States, have long slender branches which bear tiny scale-like leaves at their nodes. Infusions from these plants have been traditionally used as a stimulant, but ephedrine is a controlled substance today in many places because of the risk of harmful or fatal overdosing. Knowledge of gnetophyte history through fossil discovery has increased since the 1980s. Gnetophyte fossils have been found that date from the Triassic. Fossils dating back to the Jurassic have been found, though whether or not they belong to the gnetophytes is uncertain. Overall, the fossil record is richest in the early Cretaceous, with fossils of plants and pollen have been found that can be assigned to the gnetophytes. With just three well-defined genera within an entire division, there still is understandable difficulty in establishing an unambiguous interrelationship among them. G. H. M. Lawrence referred to them as an order, but remarked that the three families were distinct enough to deserve recognition as separate orders.
Foster & Gifford accepted this principle, placed the three orders together in a common class for convenience, which they called Gnetopsida. In general the evolutionary relationships among the seed plants still are unresolved, the Gnetophyta have played an important role in the formation of phylogenetic hypotheses. Molecular phylogenies of extant gymnosperms have conflicted with morphological characters with regard to whether the gymnosperms as a whole comprise a monophyletic group or a paraphyletic one that gave rise to angiosperms. At issue is whether the Gnetophyta are the sister group of angiosperms, or whether they are sister to, or nested within, other extant gymnosperms. Numerous fossil gymnosperm clades once existed that are morphologically at least as distinctive as the four living gymnosperm groups, such as Bennettitales and the glossopterids; when these gymnosperm fossils are considered, the question of gnetophyte relationships to other seed plants becomes more complicated. Several hypotheses, illustrated below, have been presented to explain seed plant evolution.
Recent research by Lee EK, Cibrian-Jaramillo A, et al. suggests that the Gnetophyta are a sister group to the rest of the gymnosperms, contradicting the anthophyte hypothesis, which held that gnetophytes were sister to the flowering plants. From the early twentieth century, the anthophyte hypothesis was the prevailing explanation for seed plant evolution, based on shared morphological characters between the gnetophytes and angiosperms. In this hypothesis, the gnetophytes, along with the extinct order Bennettitales, are sister to the angiosperms, forming the "anthophytes"; some morphological characters that were suggested to unite the anthophytes include vessels in wood, net-veined leaves, lignin chemistry, the layering of cells in the apical meristem and megaspore features, short cambial initials, lignin syringal groups. However, most genetic studies, as well as more recent morphological analyses, have rejected the anthophyte hypothesis. Several of these studies have suggested that the gnet
Probergrothius angolensis, sometimes known as the Welwitschia bug, is a species of true bug found in the Namib desert and nearby regions. The species has been recognized under a misattributed name, Probergrothius sexpunctatus, for several decades, but sexpunctatus is a separate species that occurs farther to the north, they are best known for their association with the unusual plant Welwitschia mirabilis endemic to the area, but it is in doubt whether they serve a role in pollination or only drink Welwitschia sap. In addition, they may spread a fungus, Aspergillus niger, in the process, harmful to developing seeds, it is yellowish with four black markings on its wings, while P. sexpunctatus is more reddish, the anterior spots are separate, so the wings have six black markings. Encyclopedia of Life entry iNaturalist entry iSpot entry
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
A seed is an embryonic plant enclosed in a protective outer covering. The formation of the seed is part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosperm plants. Seeds are the product of the ripened ovule, after fertilization by pollen and some growth within the mother plant; the embryo is developed from the seed coat from the integuments of the ovule. Seeds have been an important development in the reproduction and success of gymnosperm and angiosperm plants, relative to more primitive plants such as ferns and liverworts, which do not have seeds and use water-dependent means to propagate themselves. Seed plants now dominate biological niches on land, from forests to grasslands both in hot and cold climates; the term "seed" has a general meaning that antedates the above – anything that can be sown, e.g. "seed" potatoes, "seeds" of corn or sunflower "seeds". In the case of sunflower and corn "seeds", what is sown is the seed enclosed in a shell or husk, whereas the potato is a tuber.
Many structures referred to as "seeds" are dry fruits. Plants producing berries are called baccate. Sunflower seeds are sometimes sold commercially while still enclosed within the hard wall of the fruit, which must be split open to reach the seed. Different groups of plants have other modifications, the so-called stone fruits have a hardened fruit layer fused to and surrounding the actual seed. Nuts are the one-seeded, hard-shelled fruit of some plants with an indehiscent seed, such as an acorn or hazelnut. Seeds are produced in several related groups of plants, their manner of production distinguishes the angiosperms from the gymnosperms. Angiosperm seeds are produced in a hard or fleshy structure called a fruit that encloses the seeds for protection in order to secure healthy growth; some fruits have layers of both fleshy material. In gymnosperms, no special structure develops to enclose the seeds, which begin their development "naked" on the bracts of cones. However, the seeds do become covered by the cone scales.
Seed production in natural plant populations varies from year to year in response to weather variables and diseases, internal cycles within the plants themselves. Over a 20-year period, for example, forests composed of loblolly pine and shortleaf pine produced from 0 to nearly 5 million sound pine seeds per hectare. Over this period, there were six bumper, five poor, nine good seed crops, when evaluated for production of adequate seedlings for natural forest reproduction. Angiosperm seeds consist of three genetically distinct constituents: the embryo formed from the zygote, the endosperm, triploid, the seed coat from tissue derived from the maternal tissue of the ovule. In angiosperms, the process of seed development begins with double fertilization, which involves the fusion of two male gametes with the egg cell and the central cell to form the primary endosperm and the zygote. Right after fertilization, the zygote is inactive, but the primary endosperm divides to form the endosperm tissue.
This tissue becomes the food the young plant will consume until the roots have developed after germination. After fertilization the ovules develop into the seeds; the ovule consists of a number of components: The funicle or seed stalk which attaches the ovule to the placenta and hence ovary or fruit wall, at the pericarp. The nucellus, the remnant of the megasporangium and main region of the ovule where the megagametophyte develops; the micropyle, a small pore or opening in the apex of the integument of the ovule where the pollen tube enters during the process of fertilization. The chalaza, the base of the ovule opposite the micropyle, where integument and nucellus are joined together; the shape of the ovules as they develop affects the final shape of the seeds. Plants produce ovules of four shapes: the most common shape is called anatropous, with a curved shape. Orthotropous ovules are straight with all the parts of the ovule lined up in a long row producing an uncurved seed. Campylotropous ovules have a curved megagametophyte giving the seed a tight "C" shape.
The last ovule shape is called amphitropous, where the ovule is inverted and turned back 90 degrees on its stalk. In the majority of flowering plants, the zygote's first division is transversely oriented in regards to the long axis, this establishes the polarity of the embryo; the upper or chalazal pole becomes the main area of growth of the embryo, while the lower or micropylar pole produces the stalk-like suspensor that attaches to the micropyle. The suspensor absorbs and manufactures nutrients from the endosperm that are used during the embryo's growth; the main components of the embryo are: The cotyledons, the seed leaves, attached to the embryonic axis. There may be two; the cotyledons are the source of nutrients in the non-endospermic dicotyledons, in which case they replace the endosperm, are thick and leathery. In endospermic seeds the cotyledons are papery. Dicotyledons have the point of attachment opposite one another on the axis; the epicotyl, the embryonic axis above the point of attachment of the cotyledon.
The plumule, the tip of the epicotyl, has a feathery appearance due to the presence of young leaf primordia at the apex, will become the shoot upon germination. The hypocotyl, the embryonic axis below the point of attachment of the cotyledon, connecting the epicotyl and the radicle, being the stem-root transition zone; the radicle, the basal tip of the hy
The flowering plants known as angiosperms, Angiospermae or Magnoliophyta, are the most diverse group of land plants, with 64 orders, 416 families 13,164 known genera and c. 369,000 known species. Like gymnosperms, angiosperms are seed-producing plants. However, they are distinguished from gymnosperms by characteristics including flowers, endosperm within the seeds, the production of fruits that contain the seeds. Etymologically, angiosperm means a plant; the term comes from the Greek words sperma. The ancestors of flowering plants diverged from gymnosperms in the Triassic Period, 245 to 202 million years ago, the first flowering plants are known from 160 mya, they diversified extensively during the Early Cretaceous, became widespread by 120 mya, replaced conifers as the dominant trees from 100 to 60 mya. Angiosperms differ from other seed plants in several ways, described in the table below; these distinguishing characteristics taken together have made the angiosperms the most diverse and numerous land plants and the most commercially important group to humans.
Angiosperm stems are made up of seven layers. The amount and complexity of tissue-formation in flowering plants exceeds that of gymnosperms; the vascular bundles of the stem are arranged such that the phloem form concentric rings. In the dicotyledons, the bundles in the young stem are arranged in an open ring, separating a central pith from an outer cortex. In each bundle, separating the xylem and phloem, is a layer of meristem or active formative tissue known as cambium. By the formation of a layer of cambium between the bundles, a complete ring is formed, a regular periodical increase in thickness results from the development of xylem on the inside and phloem on the outside; the soft phloem becomes crushed, but the hard wood persists and forms the bulk of the stem and branches of the woody perennial. Owing to differences in the character of the elements produced at the beginning and end of the season, the wood is marked out in transverse section into concentric rings, one for each season of growth, called annual rings.
Among the monocotyledons, the bundles are more numerous in the young stem and are scattered through the ground tissue. They once formed the stem increases in diameter only in exceptional cases; the characteristic feature of angiosperms is the flower. Flowers show remarkable variation in form and elaboration, provide the most trustworthy external characteristics for establishing relationships among angiosperm species; the function of the flower is to ensure fertilization of the ovule and development of fruit containing seeds. The floral apparatus may arise terminally from the axil of a leaf; as in violets, a flower arises singly in the axil of an ordinary foliage-leaf. More the flower-bearing portion of the plant is distinguished from the foliage-bearing or vegetative portion, forms a more or less elaborate branch-system called an inflorescence. There are two kinds of reproductive cells produced by flowers. Microspores, which will divide to become pollen grains, are the "male" cells and are borne in the stamens.
The "female" cells called megaspores, which will divide to become the egg cell, are contained in the ovule and enclosed in the carpel. The flower may consist only of these parts, as in willow, where each flower comprises only a few stamens or two carpels. Other structures are present and serve to protect the sporophylls and to form an envelope attractive to pollinators; the individual members of these surrounding structures are known as petals. The outer series is green and leaf-like, functions to protect the rest of the flower the bud; the inner series is, in general, white or brightly colored, is more delicate in structure. It functions to attract bird pollinators. Attraction is effected by color and nectar, which may be secreted in some part of the flower; the characteristics that attract pollinators account for the popularity of flowers and flowering plants among humans. While the majority of flowers are perfect or hermaphrodite, flowering plants have developed numerous morphological and physiological mechanisms to reduce or prevent self-fertilization.
Heteromorphic flowers have short carpels and long stamens, or vice versa, so animal pollinators cannot transfer pollen to the pistil. Homomorphic flowers may employ a biochemical mechanism called self-incompatibility to discriminate between self and non-self pollen grains. In other species, the male and female parts are morphologically separated, developing on different flowers; the botanical term "Angiosperm", from the Ancient Greek αγγείον, angeíon and σπέρμα, was coined in the form Angiospermae by Paul Hermann in 1690, as the name of one of his primary divisions of the plant kingdom. This included flowering plants possessing seeds enclosed in capsules, distinguished from his Gymnospermae, or flowering plants with achenial or schizo-carpic fruits, the whole fruit or each of its pieces being here regarded as a seed and naked; the term and its antonym were maintained by Carl Linnaeus with the same sense, but with restricted application, in the names of the orders of his class Didynamia. Its use with any