A tepal is one of the outer parts of a flower. The term is used when these parts cannot be classified as either sepals or petals; this may be because the parts of the perianth are undifferentiated, as in Magnolia, or because, although it is possible to distinguish an outer whorl of sepals from an inner whorl of petals, the sepals and petals have similar appearance to one another. The term was first proposed by Augustin Pyramus de Candolle in 1827 and was constructed by analogy with the terms "petal" and "sepal". Undifferentiated tepals are believed to be the ancestral condition in flowering plants. For example, thought to have separated earliest in the evolution of flowering plants, has flowers with undifferentiated tepals. Distinct petals and sepals would therefore have arisen by differentiation in response to animal pollination. In typical modern flowers, the outer or enclosing whorl of organs forms sepals, specialised for protection of the flower bud as it develops, while the inner whorl forms petals, which attract pollinators.
Tepals formed by similar sepals and petals are common in monocotyledons the "lilioid monocots". In tulips, for example, the first and second whorls both contain structures; these are fused at the base to form one large, six-parted structure. In lilies the organs in the first whorl are separate from the second, but all look similar, thus all the showy parts are called tepals. Where sepals and petals can in principle be distinguished, usage of the term "tepal" is not always consistent – some authors will refer to "sepals and petals" where others use "tepals" in the same context. In some plants the flowers have no petals, all the tepals are sepals modified to look like petals; these organs are described for example, the sepals of hellebores. When the undifferentiated tepals resemble petals, they are referred to as "petaloid", as in petaloid monocots, orders of monocots with brightly coloured tepals. Since they include Liliales, an alternative name is lilioid monocots. Terms used in the description of tepals include pubescent and puberulous.
Tepal shape is described in similar terms to those used for leaves. Flowers with tepals Glossary of plant morphology Plant reproductive morphology Botany: A Brief Introduction To Plant Biology - 5th ed. Thomas L. Rost. Plant Systematics - Jones.
Magnolia is a large genus of about 210 flowering plant species in the subfamily Magnolioideae of the family Magnoliaceae. It is named after French botanist Pierre Magnol. Magnolia is an ancient genus. Appearing before bees did, the flowers are theorized to have evolved to encourage pollination by beetles. To avoid damage from pollinating beetles, the carpels of Magnolia flowers are tough. Fossilized specimens of M. acuminata have been found dating to 20 million years ago, of plants identifiably belonging to the Magnoliaceae date to 95 million years ago. Another aspect of Magnolia considered to represent an ancestral state is that the flower bud is enclosed in a bract rather than in sepals. Magnolia shares the tepal characteristic with several other flowering plants near the base of the flowering plant lineage such as Amborella and Nymphaea; the natural range of Magnolia species is a disjunct distribution, with a main center in east and southeast Asia and a secondary center in eastern North America, Central America, the West Indies, some species in South America.
As with all Magnoliaceae, the perianth is undifferentiated, with 9–15 tepals in 3 or more whorls. The flowers are bisexual with numerous adnate carpels and stamens are arranged in a spiral fashion on the elongated receptacle; the fruit dehisces along the dorsal sutures of the carpels. The pollen is monocolpate, the embryo development is of the Polygonum type; the name Magnolia first appeared in 1703 in the Genera of Charles Plumier, for a flowering tree from the island of Martinique. English botanist William Sherard, who studied botany in Paris under Joseph Pitton de Tournefort, a pupil of Magnol, was most the first after Plumier to adopt the genus name Magnolia, he was at least responsible for the taxonomic part of Johann Jacob Dillenius's Hortus Elthamensis and of Mark Catesby's Natural History of Carolina and the Bahama Islands. These were the first works after Plumier's Genera that used the name Magnolia, this time for some species of flowering trees from temperate North America; the species that Plumier named Magnolia was described as Annona dodecapetala by Lamarck, has since been named Magnolia plumieri and Talauma plumieri but is now known as Magnolia dodecapetala.
Carl Linnaeus, familiar with Plumier's Genera, adopted the genus name Magnolia in 1735 in his first edition of Systema Naturae, without a description, but with a reference to Plumier's work. In 1753, he took up Plumier's Magnolia in the first edition of Species Plantarum. There he described a monotypic genus, with the sole species being Magnolia virginiana. Since Linnaeus never saw a herbarium specimen of Plumier's Magnolia and had only his description and a rather poor picture at hand, he must have taken it for the same plant, described by Catesby in his 1730 Natural History of Carolina, he placed it in the synonymy of Magnolia virginiana var. fœtida, the taxon now known as Magnolia grandiflora. Under Magnolia virginiana Linnaeus described five varieties. In the tenth edition of Systema Naturae, he merged grisea with glauca, raised the four remaining varieties to species status. By the end of the 18th century and plant hunters exploring Asia began to name and describe the Magnolia species from China and Japan.
The first Asiatic species to be described by western botanists were Magnolia denudata and Magnolia liliiflora, Magnolia coco and Magnolia figo. Soon after that, in 1794, Carl Peter Thunberg collected and described Magnolia obovata from Japan and at the same time Magnolia kobus was first collected. With the number of species increasing, the genus was divided into the two subgenera Magnolia and Yulania. Magnolia contains the American evergreen species M. grandiflora, of horticultural importance in the southeastern United States, M. virginiana, the type species. Yulania contains several deciduous Asiatic species, such as M. denudata and M. kobus, which have become horticulturally important in their own right and as parents in hybrids. Classified in Yulania, is the American deciduous M. acuminata, which has attained greater status as the parent responsible for the yellow flower colour in many new hybrids. Relations in the family Magnoliaceae have been puzzling taxonomists for a long time; because the family is quite old and has survived many geological events, its distribution has become scattered.
Some species or groups of species have been isolated for a long time, while others could stay in close contact. To create divisions in the family based upon morphological characters, has proven to be a nearly impossible task. By the end of the 20th century, DNA sequencing had become available as a method of large-scale research on phylogenetic relationships. Several studies, including studies on many species in the family Magnoliaceae, were carried out to investigate relationships. What these studies all revealed was that genus Michelia and Magnolia subgenus Yulania were far more allied to each other than either one of them was to Magnolia subgenus Magnolia; these phylogenetic studies were supported by morphological data. As nomenclature is supposed to reflect relationships, the situation with the species names in Michelia and Magnolia subgenus Yulania was undesirable. Taxonomically, three choices are available: 1 to join Michelia and Yulania species in a common genus, not being Magnolia (for
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
The pappus is the modified calyx, the part of an individual floret, that surrounds the base of the corolla tube in flower heads of the plant family Asteraceae. The term is sometimes used in other plant families such as Asclepiadaceae, whose seeds have a similar structure attached, although it is not related to the calyx of the flower; the Asteraceae pappus may be composed of bristles, scales, or may be absent. In some species, the pappus is too small to see without magnification. In species such as Dandelion or Eupatorium, feathery bristles of the pappus function as a "parachute" which enables the seed to be carried by the wind; the name derives from the Ancient Greek word pappos, Latin pappus, meaning "old man", so used for a plant having bristles and for the woolly, hairy seed of certain plants. Asteraceae morphology Composite flowers
Lilioid monocots is an informal name used for a grade of five monocot orders in which the majority of species have flowers with large, coloured tepals. This characteristic is similar to that found in lilies. Petaloid monocots refers to the flowers having tepals; the taxonomic terms Lilianae or Liliiflorae have been applied to this assemblage at various times. From the early nineteenth century many of the species in this group of plants were put into a broadly defined family, Liliaceae sensu lato or s.l.. These classification systems are still found in other sources. Within the monocots the Liliaceae s.l. were distinguished from the Glumaceae. The development of molecular phylogenetics, cladistic theory and phylogenetic methods in the 1990s resulted in a dismemberment of the Liliaceae and its subsequent redistribution across three lilioid orders. Subsequent work has shown that two other more recognized orders and Pandanales segregate with this group, resulting in the modern concept of five constituent orders within the lilioid monocot assemblage.
This has resulted in treating monocots as three informal groups, alismatid and commelinid monocots. The lilioids are paraphyletic in the sense; the descriptive term "petaloid lilioid monocot" relates to the conspicuous petal-like tepals which superficially resemble true lilies. Morphologically, the petaloid or lilioid monocots can be considered to possess five groups of three-fold whorls. Lilioid monocots all have flowers which can be considered to have been derived from a lily-like flower with six similar tepals, six stamens; the typical lilioid gynoecium has three carpels fused into a superior trilocular superior ovary, axile placentation, a single hollow style, several ovules with anatropous orientation in one or two rows per locule and nectaries at the base. However, floral synapomorphy is rare; this pattern is ancestral for the lilioid monocots. Structural monosymmetry is rare. Various trends are apparent among the lilioids, notably a change to an inferior ovary and a reduction of the number of stamens to three.
In some groups, the tepals have become differentiated, so that the flower has three coloured petals and three smaller green sepals. All lilioid monocots retain at least three petal-like tepals. Since some commelinids have petaloid flowers, the term'lilioid' is a more accurate one for the group which excludes them, since the term petaloid monocot is still used in describing commelinids; the morphological concept of petaloid monocots has been equated with "animal-attracting" as opposed to wind-pollinating plants that have evolved different floral structures. Pollen structure shows that of the two main tapetum types and plasmodial, the lilioid monocots are nearly all secretory. In the orders that branched off before the lilioid monocots, the Acorales and Alismatales, flowers differ in several ways. In some cases, like Acorus, they have become insignificant. In others, like Butomus, they have six coloured tepals, so could be called'petaloid', but stamens and carpels are more numerous than in the lilioid monocots.
The evolved commelinids have various kinds of flower, few of which are'lily-like'. In the order Poales, comprising grasses and sedges, flowers are either petal-less or have small, unshowy petals. Many Zingiberales species have brightly showy flowers. However, their apparent structure is misleading. For example, the six tepals of cannas are small and hidden under expanded and brightly coloured stamens or staminodes which resemble petals and may be mistaken for them. In one of the earliest monocot taxonomies, that of John Lindley, the grouping corresponding to the lilioid monocots was the "tribe" Petaloideae. In Lindley's system the monocots consisted of two tribes, the Petaloideae, the Glumaceae. Lindley divided the Petaloideae into 32 the Glumaceae into two further orders. Various successive taxonomies of the monocots emphasized the grouping of species with petaloid perianths, such as Bentham and Hooker's Coronarieæ and Hutchinson's Corolliferae. Hence the concept that there was a natural grouping of monocots whose flowers were predominantly petaloid, gave notion to the term "petaloid monocots".
The core group of petaloids were the Liliaceae, hence "lilioid monocots". The term "lilioid monocot" or lilioid" has had varying interpretations. One of the narrower applications is "lily-like" monocots, meaning the two orders Asparagales and Liliales, but the term has been applied to Takhtajan's superorder Lilianae, the whole of Liliales, or restricted to Cronquist's broadly defined Liliaceae. Although "petaloid" and "lilioid" have been used interchangeably, as Heywood points out, some usages of "petaloid monocot" in horticulture, are so broad as to be meaningless in that it had been used to refer to all species with conspicuous petals or perianth segments, which would cover a broad swathe of families (he estimated three dozen across many o
A meristem is the tissue in most plants containing undifferentiated cells, found in zones of the plant where growth can take place. Meristematic cells are responsible for growth. Differentiated plant cells cannot divide or produce cells of a different type. Meristematic cells are incompletely or not at all differentiated, are capable of continued cellular division. Therefore, cell division in the meristem is required to provide new cells for expansion and differentiation of tissues and initiation of new organs, providing the basic structure of the plant body. Furthermore, the cells are small and protoplasm fills the cell completely; the vacuoles are small. The cytoplasm does not contain differentiated plastids, although they are present in rudimentary form. Meristematic cells are packed together without intercellular cavities; the cell wall is a thin primary cell wall as well as some are thick in some plants. Maintenance of the cells requires a balance between two antagonistic processes: organ initiation and stem cell population renewal.
There are three types of meristematic tissues: apical and lateral. At the meristem summit, there is a small group of dividing cells, called the central zone. Cells of this zone are essential for meristem maintenance; the proliferation and growth rates at the meristem summit differ from those at the periphery. The term meristem was first used in 1858 by Carl Wilhelm von Nägeli in his book Beiträge zur Wissenschaftlichen Botanik, it is derived from the Greek word merizein, meaning to divide, in recognition of its inherent function. Apical meristems are the undifferentiated meristems in a plant; these differentiate into three kinds of primary meristems. The primary meristems in turn produce the two secondary meristem types; these secondary meristems are known as lateral meristems because they are involved in lateral growth. There are two types of apical meristem tissue: shoot apical meristem, which gives rise to organs like the leaves and flowers, root apical meristem, which provides the meristematic cells for future root growth.
SAM and RAM cells divide and are considered indeterminate, in that they do not possess any defined end status. In that sense, the meristematic cells are compared to the stem cells in animals, which have an analogous behavior and function; the number of layers varies according to plant type. In general the outermost layer is called the tunica. In monocots, the tunica determine the physical characteristics of the leaf margin. In dicots, layer two of the corpus determine the characteristics of the edge of the leaf; the corpus and tunica play a critical part of the plant physical appearance as all plant cells are formed from the meristems. Apical meristems are found in two locations: the stem; some Arctic plants have an apical meristem in the lower/middle parts of the plant. It is thought. Shoot apical meristems are the source such as leaves and flowers. Cells at the shoot apical meristem summit serve as stem cells to the surrounding peripheral region, where they proliferate and are incorporated into differentiating leaf or flower primordia.
The shoot apical meristem is the site of most of the embryogenesis in flowering plants. Primordia of leaves, petals and ovaries are initiated here at the rate of one every time interval, called a plastochron, it is. One of these indications might be the loss of apical dominance and the release of otherwise dormant cells to develop as auxiliary shoot meristems, in some species in axils of primordia as close as two or three away from the apical dome; the shoot apical meristem consists of 4 distinct cell groups: Stem cells The immediate daughter cells of the stem cells A subjacent organizing center Founder cells for organ initiation in surrounding regionsThe four distinct zones mentioned above are maintained by a complex signalling pathway. In Arabidopsis thaliana, 3 interacting CLAVATA genes are required to regulate the size of the stem cell reservoir in the shoot apical meristem by controlling the rate of cell division. CLV1 and CLV2 are predicted to form a receptor complex to. CLV3 shares some homology with the ESR proteins of maize, with a short 14 amino acid region being conserved between the proteins.
Proteins that contain these conserved regions have been grouped into the CLE family of proteins. CLV1 has been shown to interact with several cytoplasmic proteins that are most involved in downstream signalling. For example, the CLV complex has been found to be associated with Rho/Rac small GTPase-related proteins; these proteins may act as an intermediate between the CLV complex and a mitogen-activated protein kinase, involved in signalling cascades. KAPP is a kinase-associated protein phosphatase, shown to interact with CLV1. KAPP is thought to act as a negative regulator of CLV1 by dephosphorylating it. Another important gene in plant meristem maintenance is WUSCHEL, a target of CLV signaling in addition to positively regulating CLV, thus forming a feedback loop. WUS is expressed in the cells below the stem cells of the meristem and its presence prevents the differentiation of the stem c
Plants are multicellular, predominantly photosynthetic eukaryotes of the kingdom Plantae. Plants were treated as one of two kingdoms including all living things that were not animals, all algae and fungi were treated as plants. However, all current definitions of Plantae exclude the fungi and some algae, as well as the prokaryotes. By one definition, plants form the clade Viridiplantae, a group that includes the flowering plants and other gymnosperms and their allies, liverworts and the green algae, but excludes the red and brown algae. Green plants obtain most of their energy from sunlight via photosynthesis by primary chloroplasts that are derived from endosymbiosis with cyanobacteria, their chloroplasts contain b, which gives them their green color. Some plants are parasitic or mycotrophic and have lost the ability to produce normal amounts of chlorophyll or to photosynthesize. Plants are characterized by sexual reproduction and alternation of generations, although asexual reproduction is common.
There are about 320 thousand species of plants, of which the great majority, some 260–290 thousand, are seed plants. Green plants provide a substantial proportion of the world's molecular oxygen and are the basis of most of Earth's ecosystems on land. Plants that produce grain and vegetables form humankind's basic foods, have been domesticated for millennia. Plants have many cultural and other uses, as ornaments, building materials, writing material and, in great variety, they have been the source of medicines and psychoactive drugs; the scientific study of plants is known as a branch of biology. All living things were traditionally placed into one of two groups and animals; this classification may date from Aristotle, who made the distincton between plants, which do not move, animals, which are mobile to catch their food. Much when Linnaeus created the basis of the modern system of scientific classification, these two groups became the kingdoms Vegetabilia and Animalia. Since it has become clear that the plant kingdom as defined included several unrelated groups, the fungi and several groups of algae were removed to new kingdoms.
However, these organisms are still considered plants in popular contexts. The term "plant" implies the possession of the following traits multicellularity, possession of cell walls containing cellulose and the ability to carry out photosynthesis with primary chloroplasts; when the name Plantae or plant is applied to a specific group of organisms or taxon, it refers to one of four concepts. From least to most inclusive, these four groupings are: Another way of looking at the relationships between the different groups that have been called "plants" is through a cladogram, which shows their evolutionary relationships; these are not yet settled, but one accepted relationship between the three groups described above is shown below. Those which have been called "plants" are in bold; the way in which the groups of green algae are combined and named varies between authors. Algae comprise several different groups of organisms which produce food by photosynthesis and thus have traditionally been included in the plant kingdom.
The seaweeds range from large multicellular algae to single-celled organisms and are classified into three groups, the green algae, red algae and brown algae. There is good evidence that the brown algae evolved independently from the others, from non-photosynthetic ancestors that formed endosymbiotic relationships with red algae rather than from cyanobacteria, they are no longer classified as plants as defined here; the Viridiplantae, the green plants – green algae and land plants – form a clade, a group consisting of all the descendants of a common ancestor. With a few exceptions, the green plants have the following features in common, they undergo closed mitosis without centrioles, have mitochondria with flat cristae. The chloroplasts of green plants are surrounded by two membranes, suggesting they originated directly from endosymbiotic cyanobacteria. Two additional groups, the Rhodophyta and Glaucophyta have primary chloroplasts that appear to be derived directly from endosymbiotic cyanobacteria, although they differ from Viridiplantae in the pigments which are used in photosynthesis and so are different in colour.
These groups differ from green plants in that the storage polysaccharide is floridean starch and is stored in the cytoplasm rather than in the plastids. They appear to have had a common origin with Viridiplantae and the three groups form the clade Archaeplastida, whose name implies that their chloroplasts were derived from a single ancient endosymbiotic event; this is the broadest modern definition of the term'plant'. In contrast, most other algae not only have different pigments but have chloroplasts with three or four surrounding membranes, they are not close relatives of the Archaeplastida having acquired chloroplasts separately from ingested or symbiotic green and red algae. They are thus not included in the broadest modern definition of the plant kingdom, although they were in the past; the green plants or Viridiplantae were traditionally divided into the green algae (including