Petals are modified leaves that surround the reproductive parts of flowers. They are brightly colored or unusually shaped to attract pollinators. Together, all of the petals of a flower are called a corolla. Petals are accompanied by another set of special leaves called sepals, that collectively form the calyx and lie just beneath the corolla; the calyx and the corolla together make up the perianth. 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 Tulipa. Conversely, genera such as Rosa and Phaseolus have well-distinguished petals; 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. Although petals are the most conspicuous parts of animal-pollinated flowers, wind-pollinated species, such as the grasses, either have small petals or lack them entirely.
The role of the corolla in plant evolution has been studied extensively since Charles Darwin postulated a theory of the origin of elongated corollae and corolla tubes. A corolla of separate tepals is apopetalous. If the petals are free from one another in the corolla, the plant is choripetalous. In the case of fused tepals, the term is syntepalous; the corolla in some plants forms a tube. Petals can differ in different species; the number of petals in a flower may hold clues to a plant's classification. For example, flowers on eudicots most have four or five petals while flowers on monocots have three or six petals, although there are many exceptions to this rule; the petal whorl or corolla may be bilaterally symmetrical. If all of the petals are identical in size and shape, the flower is said to be regular or actinomorphic. Many flowers are termed irregular or zygomorphic. In irregular flowers, other floral parts may be modified from the regular form, but the petals show the greatest deviation from radial symmetry.
Examples of zygomorphic flowers may be seen in members of the pea family. In many plants of the aster family such as the sunflower, Helianthus annuus, the circumference of the flower head is composed of ray florets; each ray floret is anatomically an individual flower with a single large petal. Florets in the centre of the disc have no or reduced petals. In some plants such as Narcissus the lower part of the petals or tepals are fused to form a floral cup above the ovary, from which the petals proper extend. Petal consists of two parts: the upper, broad part, similar to leaf blade called the blade and the lower part, similar to leaf petiole, called the claw, separated from each other at the limb. Claws are developed in petals of some flowers such as Erysimum cheiri; the inception and further development of petals shows a great variety of patterns. Petals of different species of plants vary in colour or colour pattern, both in visible light and in ultraviolet; such patterns function as guides to pollinators, are variously known as nectar guides, pollen guides, floral guides.
The genetics behind the formation of petals, in accordance with the ABC model of flower development, are that sepals, petals and carpels are modified versions of each other. It appears that the mechanisms to form petals evolved few times, rather than evolving from stamens. Pollination is an important step in the sexual reproduction of higher plants. Pollen is produced by the male organs of hermaphroditic flowers. Pollen does not move on its own and thus requires wind or animal pollinators to disperse the pollen to the stigma of the same or nearby flowers. However, pollinators are rather selective in determining the flowers; this develops competition between flowers and as a result flowers must provide incentives to appeal to pollinators. Petals play a major role in competing to attract pollinators. Henceforth pollination dispersal could occur and the survival of many species of flowers could prolong. Petals have various purposes depending on the type of plant. In general, petals operate to protect some parts of the flower and attract/repel specific pollinators.
This is where the positioning of the flower petals are located on the flower is the corolla e.g. the buttercup having shiny yellow flower petals which contain guidelines amongst the petals in aiding the pollinator towards the nectar. Pollinators have the ability to determine specific flowers. Using incentives flowers draw pollinators and set up a mutual relation between each other in which case the pollinators will remember to always guard and pollinate these flowers; the petals could produce different scents to allure desirable pollinators or repel undesirable pollinators. Some flowers will mimic the scents produced by materials such as decaying meat, to attract pollinators to them. Various colour traits are used by different petals that could attract pollinators that have poor smelling abilities, or that only come out at certain parts of the day; some flowers are able to change the colour
A sepal is a part of the flower of angiosperms. Green, sepals function as protection for the flower in bud, as support for the petals when in bloom; the term sepalum was coined by Noël Martin Joseph de Necker in 1790, derived from the Greek σκεπη, a covering. Collectively the sepals are called the outermost whorl of parts that form a flower; the word calyx was adopted from the Latin calyx, not to be confused with a cup or goblet. Calyx derived from the Greek κάλυξ, a bud, a calyx, a husk or wrapping, while calix derived from the Greek κυλιξ, a cup or goblet, the words have been used interchangeably in botanical Latin. After flowering, most plants have no more use for the calyx which becomes vestigial; some plants retain a thorny calyx, either dried or live, as protection for seeds. Examples include species of Acaena, some of the Solanaceae, the water caltrop, Trapa natans. In some species the calyx not only persists after flowering, but instead of withering, begins to grow until it forms a bladder-like enclosure around the fruit.
This is an effective protection against some kinds of birds and insects, for example in Hibiscus trionum and the Cape gooseberry. Morphologically, both sepals and petals are modified leaves; the calyx and the corolla are the outer sterile whorls of the flower, which together form what is known as the perianth. The term tepal is applied when the parts of the perianth are difficult to distinguish, e.g. the petals and sepals share the same color, or the petals are absent and the sepals are colorful. 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. Examples of plants in which the term tepal is appropriate include genera such as Tulipa. In contrast, genera such as Rosa and Phaseolus have well-distinguished petals; the number of sepals in a flower is its merosity. Flower merosity is indicative of a plant's classification.
The merosity of a eudicot flower is four or five. The merosity of a monocot or palaeodicot flower is a multiple of three; the development and form of the sepals vary among flowering plants. They may be fused together; the sepals are much reduced, appearing somewhat awn-like, or as scales, teeth, or ridges. Most such structures protrude until the fruit is mature and falls off. Examples of flowers with much reduced perianths are found among the grasses. In some flowers, the sepals are fused towards the base. In other flowers a hypanthium includes the bases of sepals and the attachment points of the stamens. Plant morphology
In botany, phyllotaxis or phyllotaxy is the arrangement of leaves on a plant stem. Phyllotactic spirals form a distinctive class of patterns in nature; the term was coined by Charles Bonnet to describe the arrangement of leaves on a plant. The basic arrangements of leaves on a stem are alternate. Leaves may be whorled if several leaves arise, or appear to arise, from the same level on a stem. With an opposite leaf arrangement, two leaves arise from the stem at the same level, on opposite sides of the stem. An opposite leaf pair can be thought of as a whorl of two leaves. With an alternate pattern, each leaf arises at a different point on the stem. Distichous phyllotaxis called "two-ranked leaf arrangement" is a special case of either opposite or alternate leaf arrangement where the leaves on a stem are arranged in two vertical columns on opposite sides of the stem. Examples include various bulbous plants such as Boophone, it occurs in other plant habits such as those of Gasteria or Aloe seedlings, in mature plants of related species such as Kumara plicatilis.
In an opposite pattern, if successive leaf pairs are 90 degrees apart, this habit is called decussate. It is common in members of the family Crassulaceae Decussate phyllotaxis occurs in the Aizoaceae. In genera of the Aizoaceae, such as Lithops and Conophytum, many species have just two developed leaves at a time, the older pair folding back and dying off to make room for the decussately oriented new pair as the plant grows; the whorled arrangement is unusual on plants except for those with short internodes. Examples of trees with whorled phyllotaxis are Brabejum stellatifolium and the related genus Macadamia. A whorl can occur as a basal structure where all the leaves are attached at the base of the shoot and the internodes are small or nonexistent. A basal whorl with a large number of leaves spread out in a circle is called a rosette; the rotational angle from leaf to leaf in a repeating spiral can be represented by a fraction of a full rotation around the stem. Alternate distichous leaves will have an angle of 1/2 of a full rotation.
In beech and hazel the angle is 1/3, in oak and apricot it is 2/5, in sunflowers and pear, it is 3/8, in willow and almond the angle is 5/13. The numerator and denominator consist of a Fibonacci number and its second successor; the number of leaves is sometimes called rank, in the case of simple Fibonacci ratios, because the leaves line up in vertical rows. With larger Fibonacci pairs, the pattern becomes non-repeating; this tends to occur with a basal configuration. Examples can be found in composite flowers and seed heads; the most famous example is the sunflower head. This phyllotactic pattern creates an optical effect of criss-crossing spirals. In the botanical literature, these designs are described by the number of counter-clockwise spirals and the number of clockwise spirals; these turn out to be Fibonacci numbers. In some cases, the numbers appear to be multiples of Fibonacci numbers because the spirals consist of whorls; the pattern of leaves on a plant is controlled by the local depletion of the plant hormone auxin in certain areas of the meristem.
Leaves become initiated in localized areas. When a leaf is initiated and begins development, auxin begins to flow towards it, thus depleting auxin from another area on the meristem where a new leaf is to be initiated; this gives rise to a self-propagating system, controlled by the ebb and flow of auxin in different regions of the meristematic topography. Insight into the mechanism had to wait until Wilhelm Hofmeister proposed a model in 1868. A primordium, the nascent leaf, forms at the least crowded part of the shoot meristem; the golden angle between successive leaves is the blind result of this jostling. Since three golden arcs add up to more than enough to wrap a circle, this guarantees that no two leaves follow the same radial line from center to edge; the generative spiral is a consequence of the same process that produces the clockwise and counter-clockwise spirals that emerge in densely packed plant structures, such as Protea flower disks or pinecone scales. In modern times, researchers such as Snow and Snow have continued these lines of inquiry.
Computer modeling and morphological studies have refined Hoffmeister's ideas. Questions remain about the details. Botanists are divided on whether the control of leaf migration depends on chemical gradients among the primordia or purely mechanical forces. Lucas rather than Fibonacci numbers have been observed in a few plants and the leaf positioning appears to be random. Physical models of phyllotaxis date back to Airy's experiment of packing hard spheres. Gerrit van Iterson diagrammed. Douady et al. showed that phyllotactic patterns emerge as self-organizing processes in dynamic systems. In 1991, Levitov proposed that lowest energy configurations of repulsive particles in cylindrical geometries reproduce the spirals of botanical phyllotaxis. More Nisoli et al. showed that to be true by constructing a "magnetic cactus" made of magnetic dipoles mounted on bearings stacked along a "stem". They demonstrated that these interacting particles can access novel dynamical phenomena beyond what botany yields: a "Dynamical Phyllotaxis" family of non local topological solitons emerge in the nonlinear regime of these systems, as well as purely classical rotons and maxons in the spectrum of linear excitations.
Close packing of spheres generates a dodecahedral tessellation with pentaprismic fac
Phytogeography or botanical geography is the branch of biogeography, concerned with the geographic distribution of plant species and their influence on the earth's surface. Phytogeography is concerned with all aspects of plant distribution, from the controls on the distribution of individual species ranges to the factors that govern the composition of entire communities and floras. Geobotany, by contrast, focuses on the geographic space's influence on plants. Phytogeography is part of a more general science known as biogeography. Phytogeographers are concerned with patterns and process in plant distribution. Most of the major questions and kinds of approaches taken to answer such questions are held in common between phyto- and zoogeographers. Phytogeography in wider sense encompasses four fields, according with the focused aspect, flora and origin, respectively: plant ecology. Historical plant geography Phytogeography is divided into two main branches: ecological phytogeography and historical phytogeography.
The former investigates the role of current day biotic and abiotic interactions in influencing plant distributions. The basic data elements of phytogeography are occurrence records with operational geographic units such as political units or geographical coordinates; these data are used to construct phytogeographic provinces and elements. The questions and approaches in phytogeography are shared with zoogeography, except zoogeography is concerned with animal distribution rather than plant distribution; the term phytogeography. How the term is applied by practicing scientists is apparent in the way periodicals use the term; the American Journal of Botany, a monthly primary research journal publishes a section titled "Systematics and Evolution." Topics covered in the American Journal of Botany's "Systematics and Phytogeography" section include phylogeography, distribution of genetic variation and, historical biogeography, general plant species distribution patterns. Biodiversity patterns are not covered.
Phytogeography has a long history. One of the subjects earliest proponents was Prussian naturalist Alexander von Humboldt, referred to as the "father of phytogeography". Von Humboldt advocated a quantitative approach to phytogeography that has characterized modern plant geography. Gross patterns of the distribution of plants became apparent early on in the study of plant geography. For example, Alfred Russel Wallace, co-discoverer of the principle of natural selection, discussed the Latitudinal gradients in species diversity, a pattern observed in other organisms as well. Much research effort in plant geography has since been devoted to understanding this pattern and describing it in more detail. In 1890, the United States Congress passed an act that appropriated funds to send expeditions to discover the geographic distributions of plants in the United States; the first of these was The Death Valley Expedition, including Frederick Vernon Coville, Frederick Funston, Clinton Hart Merriam, others.
Research in plant geography has been directed to understanding the patterns of adaptation of species to the environment. This is done chiefly by describing geographical patterns of trait/environment relationships; these patterns termed ecogeographical rules when applied to plants represent another area of phytogeography. A new field termed macroecology has developed, which focuses on broad-scale patterns and phenomena in ecology. Macroecology focuses as much on other organisms as plants. Floristics is a study of the flora of some area. Traditional phytogeography concerns itself with floristics and floristic classification, see floristic province. Biogeography Botany Geobotanical prospecting Macroecology Species distribution Zoogeography Association Brown, James H.. "Chapter 1". Biogeography. Sunderland, Massachusetts: Sinauer Associates. ISBN 0878930736. Humbodlt, Alexander von. Essai sur la geographie des plantes. Accompagné d'un tableau physique des régions équinoxiales fondé sur des mesures exécutées, depuis le dixiéme degré de latitude boréale jusqu'au dixiéme degré de latitude australe, pendant les années 1799, 1800, 1801, 1802 et 1803.
Paris: Schöll. Polunin, Nicholas. Introduction to Plant Geography and Some Related Sciences. McGraw-Hill. Wallace, Alfred R.. Tropical Nature, Other Essays. London: Macmillan. Clements, Frederic E.. "Plant Geography". Encyclopedia Americana. "Distribution of Plants". New International Encyclopedia. 1905
Vascular plants known as tracheophytes, form a large group of plants that are defined as those land plants that have lignified tissues for conducting water and minerals throughout the plant. They have a specialized non-lignified tissue to conduct products of photosynthesis. Vascular plants include the clubmosses, ferns and angiosperms. Scientific names for the group include Tracheophyta and Equisetopsida sensu lato; the term higher plants should be avoided as a synonym for vascular plants as it is a remnant of the abandoned concept of the great chain of being. Vascular plants are defined by three primary characteristics: Vascular plants have vascular tissues which distribute resources through the plant; this feature allows vascular plants to evolve to a larger size than non-vascular plants, which lack these specialized conducting tissues and are thereby restricted to small sizes. In vascular plants, the principal generation phase is the sporophyte, which produce spores and is diploid. By contrast, the principal generation phase in non-vascular plants is the gametophyte, which produces gametes and is haploid.
They have true roots and stems if one or more of these traits are secondarily lost in some groups. The formal definition of the division Tracheophyta encompasses both these characteristics in the Latin phrase "facies diploida xylem et phloem instructa". One possible mechanism for the presumed switch from emphasis on the haploid generation to emphasis on the diploid generation is the greater efficiency in spore dispersal with more complex diploid structures. In other words, elaboration of the spore stalk enabled the production of more spores, enabled the development of the ability to release them higher and to broadcast them farther; such developments may include more photosynthetic area for the spore-bearing structure, the ability to grow independent roots, woody structure for support, more branching. A proposed phylogeny of the vascular plants after Kenrick and Crane is as follows, with modification to the gymnosperms from Christenhusz et al. Pteridophyta from Smith et al. and lycophytes and ferns by Christenhusz et al.
This phylogeny is supported by several molecular studies. Other researchers state that taking fossils into account leads to different conclusions, for example that the ferns are not monophyletic. Water and nutrients in the form of inorganic solutes are drawn up from the soil by the roots and transported throughout the plant by the xylem. Organic compounds such as sucrose produced by photosynthesis in leaves are distributed by the phloem sieve tube elements; the xylem consists of vessels in flowering plants and tracheids in other vascular plants, which are dead hard-walled hollow cells arranged to form files of tubes that function in water transport. A tracheid cell wall contains the polymer lignin; the phloem however consists of living cells called sieve-tube members. Between the sieve-tube members are sieve plates, which have pores to allow molecules to pass through. Sieve-tube members lack such organs as nuclei or ribosomes, but cells next to them, the companion cells, function to keep the sieve-tube members alive.
The most abundant compound in all plants, as in all cellular organisms, is water which serves an important structural role and a vital role in plant metabolism. Transpiration is the main process of water movement within plant tissues. Water is transpired from the plant through its stomata to the atmosphere and replaced by soil water taken up by the roots; the movement of water out of the leaf stomata creates a transpiration pull or tension in the water column in the xylem vessels or tracheids. The pull is the result of water surface tension within the cell walls of the mesophyll cells, from the surfaces of which evaporation takes place when the stomata are open. Hydrogen bonds exist between water molecules; the draw of water upwards may be passive and can be assisted by the movement of water into the roots via osmosis. Transpiration requires little energy to be used by the plant. Transpiration assists the plant in absorbing nutrients from the soil as soluble salts. Living root cells passively absorb water in the absence of transpiration pull via osmosis creating root pressure.
It is possible for there to be no evapotranspiration and therefore no pull of water towards the shoots and leaves. This is due to high temperatures, high humidity, darkness or drought. Xylem and phloem tissues are involved in the conduction processes within plants. Sugars are conducted throughout the plant in the phloem and other nutrients through the xylem. Conduction occurs from a source to a sink for each separate nutrient. Sugars are produced in the leaves by photosynthesis and transported to the growing shoots and roots for use in growth, cellular respiration or storage. Minerals are transported to the shoots to allow cell division and growth. Fern allies Non-vascular plant “Higher plants” or “vascular plants”
Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the phloem; these two tissues transport fluid and nutrients internally. There are two meristems associated with vascular tissue: the vascular cambium and the cork cambium. All the vascular tissues within a particular plant together constitute the vascular tissue system of that plant; the cells in vascular tissue are long and slender. Since the xylem and phloem function in the conduction of water and nutrients throughout the plant, it is not surprising that their form should be similar to pipes; the individual cells of phloem are connected end-to-end. As the plant grows, new vascular tissue differentiates in the growing tips of the plant; the new tissue is aligned with existing vascular tissue, maintaining its connection throughout the plant. The vascular tissue in plants is arranged in discrete strands called vascular bundles; these bundles include both phloem, as well as supporting and protective cells.
In stems and roots, the xylem lies closer to the interior of the stem with phloem towards the exterior of the stem. In the stems of some Asterales dicots, there may be phloem located inwardly from the xylem as well. Between the xylem and phloem is a meristem called the vascular cambium; this tissue divides off cells that will become additional phloem. This growth increases the girth of the plant, rather than its length; as long as the vascular cambium continues to produce new cells, the plant will continue to grow more stout. In trees and other plants that develop wood, the vascular cambium allows the expansion of vascular tissue that produces woody growth; because this growth ruptures the epidermis of the stem, woody plants have a cork cambium that develops among the phloem. The cork cambium gives rise to thickened cork cells to protect the surface of the plant and reduce water loss. Both the production of wood and the production of cork are forms of secondary growth. In leaves, the vascular bundles are located among the spongy mesophyll.
The xylem is oriented toward the adaxial surface of the leaf, phloem is oriented toward the abaxial surface of the leaf. This is why aphids are found on the undersides of the leaves rather than on the top, since the phloem transports sugars manufactured by the plant and they are closer to the lower surface. Xylem Phloem Cork cambium Vascular cambium Vascular plant Stele Circulatory system Intro to Plant Structure Contains diagrams of the plant tissues, listed as an outline
Plant morphology or phytomorphology is the study of the physical form and external structure of plants. This is considered distinct from plant anatomy, the study of the internal structure of plants at the microscopic level. Plant morphology is useful in the visual identification of plants. Plant morphology "represents a study of the development and structure of plants, and, by implication, an attempt to interpret these on the basis of similarity of plan and origin". There are four major areas of investigation in plant morphology, each overlaps with another field of the biological sciences. First of all, morphology is comparative, meaning that the morphologist examines structures in many different plants of the same or different species draws comparisons and formulates ideas about similarities; when structures in different species are believed to exist and develop as a result of common, inherited genetic pathways, those structures are termed homologous. For example, the leaves of pine and cabbage all look different, but share certain basic structures and arrangement of parts.
The homology of leaves is an easy conclusion to make. The plant morphologist goes further, discovers that the spines of cactus share the same basic structure and development as leaves in other plants, therefore cactus spines are homologous to leaves as well; this aspect of plant morphology overlaps with the study of plant paleobotany. Secondly, plant morphology observes both the vegetative structures of plants, as well as the reproductive structures; the vegetative structures of vascular plants includes the study of the shoot system, composed of stems and leaves, as well as the root system. The reproductive structures are more varied, are specific to a particular group of plants, such as flowers and seeds, fern sori, moss capsules; the detailed study of reproductive structures in plants led to the discovery of the alternation of generations found in all plants and most algae. This area of plant morphology overlaps with the study of plant systematics. Thirdly, plant morphology studies plant structure at a range of scales.
At the smallest scales are ultrastructure, the general structural features of cells visible only with the aid of an electron microscope, cytology, the study of cells using optical microscopy. At this scale, plant morphology overlaps with plant anatomy as a field of study. At the largest scale is the study of plant growth habit, the overall architecture of a plant; the pattern of branching in a tree will vary from species to species, as will the appearance of a plant as a tree, herb, or grass. Fourthly, plant morphology examines the pattern of development, the process by which structures originate and mature as a plant grows. While animals produce all the body parts they will have from early in their life, plants produce new tissues and structures throughout their life. A living plant always has embryonic tissues; the way in which new structures mature as they are produced may be affected by the point in the plant's life when they begin to develop, as well as by the environment to which the structures are exposed.
A morphologist studies this process, the causes, its result. This area of plant morphology overlaps with plant ecology. A plant morphologist makes comparisons between structures in many different plants of the same or different species. Making such comparisons between similar structures in different plants tackles the question of why the structures are similar, it is quite that similar underlying causes of genetics, physiology, or response to the environment have led to this similarity in appearance. The result of scientific investigation into these causes can lead to one of two insights into the underlying biology: Homology - the structure is similar between the two species because of shared ancestry and common genetics. Convergence - the structure is similar between the two species because of independent adaptation to common environmental pressures. Understanding which characteristics and structures belong to each type is an important part of understanding plant evolution; the evolutionary biologist relies on the plant morphologist to interpret structures, in turn provides phylogenies of plant relationships that may lead to new morphological insights.
When structures in different species are believed to exist and develop as a result of common, inherited genetic pathways, those structures are termed homologous. For example, the leaves of pine and cabbage all look different, but share certain basic structures and arrangement of parts; the homology of leaves is an easy conclusion to make. The plant morphologist goes further, discovers that the spines of cactus share the same basic structure and development as leaves in other plants, therefore cactus spines are homologous to leaves as well; when structures in different species are believed to exist and develop as a result of common adaptive responses to environmental pressure, those structures are termed convergent. For example, the fronds of Bryopsis plumosa and stems of Asparagus setaceus both have the same feathery branching appearance though one is an alga and one is a flowering plant; the similarity in overall structure occurs independently as a result of convergence. The growth form of many cacti and species of Euphorbia is similar though they belong to distant families.
The similarity results from common solutions to the problem of surviving in a dry environment. Plant morphology treats both the vegetative structures of plants, as well as the reproductive structures; the vegetative structures of vascular plants include two major organ systems: a shoot system, composed o