Botany called plant science, plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist; the term "botany" comes from the Ancient Greek word βοτάνη meaning "pasture", "grass", or "fodder". Traditionally, botany has included the study of fungi and algae by mycologists and phycologists with the study of these three groups of organisms remaining within the sphere of interest of the International Botanical Congress. Nowadays, botanists study 410,000 species of land plants of which some 391,000 species are vascular plants, 20,000 are bryophytes. Botany originated in prehistory as herbalism with the efforts of early humans to identify – and cultivate – edible and poisonous plants, making it one of the oldest branches of science. Medieval physic gardens attached to monasteries, contained plants of medical importance, they were forerunners of the first botanical gardens attached to universities, founded from the 1540s onwards.
One of the earliest was the Padua botanical garden. These gardens facilitated the academic study of plants. Efforts to catalogue and describe their collections were the beginnings of plant taxonomy, led in 1753 to the binomial system of Carl Linnaeus that remains in use to this day. In the 19th and 20th centuries, new techniques were developed for the study of plants, including methods of optical microscopy and live cell imaging, electron microscopy, analysis of chromosome number, plant chemistry and the structure and function of enzymes and other proteins. In the last two decades of the 20th century, botanists exploited the techniques of molecular genetic analysis, including genomics and proteomics and DNA sequences to classify plants more accurately. Modern botany is a broad, multidisciplinary subject with inputs from most other areas of science and technology. Research topics include the study of plant structure and differentiation, reproduction and primary metabolism, chemical products, diseases, evolutionary relationships and plant taxonomy.
Dominant themes in 21st century plant science are molecular genetics and epigenetics, which are the mechanisms and control of gene expression during differentiation of plant cells and tissues. Botanical research has diverse applications in providing staple foods, materials such as timber, rubber and drugs, in modern horticulture and forestry, plant propagation and genetic modification, in the synthesis of chemicals and raw materials for construction and energy production, in environmental management, the maintenance of biodiversity. Botany originated as the study and use of plants for their medicinal properties. Many records of the Holocene period date early botanical knowledge as far back as 10,000 years ago; this early unrecorded knowledge of plants was discovered in ancient sites of human occupation within Tennessee, which make up much of the Cherokee land today. The early recorded history of botany includes many ancient writings and plant classifications. Examples of early botanical works have been found in ancient texts from India dating back to before 1100 BC, in archaic Avestan writings, in works from China before it was unified in 221 BC.
Modern botany traces its roots back to Ancient Greece to Theophrastus, a student of Aristotle who invented and described many of its principles and is regarded in the scientific community as the "Father of Botany". His major works, Enquiry into Plants and On the Causes of Plants, constitute the most important contributions to botanical science until the Middle Ages seventeen centuries later. Another work from Ancient Greece that made an early impact on botany is De Materia Medica, a five-volume encyclopedia about herbal medicine written in the middle of the first century by Greek physician and pharmacologist Pedanius Dioscorides. De Materia Medica was read for more than 1,500 years. Important contributions from the medieval Muslim world include Ibn Wahshiyya's Nabatean Agriculture, Abū Ḥanīfa Dīnawarī's the Book of Plants, Ibn Bassal's The Classification of Soils. In the early 13th century, Abu al-Abbas al-Nabati, Ibn al-Baitar wrote on botany in a systematic and scientific manner. In the mid-16th century, "botanical gardens" were founded in a number of Italian universities – the Padua botanical garden in 1545 is considered to be the first, still in its original location.
These gardens continued the practical value of earlier "physic gardens" associated with monasteries, in which plants were cultivated for medical use. They supported the growth of botany as an academic subject. Lectures were given about the plants grown in the gardens and their medical uses demonstrated. Botanical gardens came much to northern Europe. Throughout this period, botany remained subordinate to medicine. German physician Leonhart Fuchs was one of "the three German fathers of botany", along with theologian Otto Brunfels and physician Hieronymus Bock. Fuchs and Brunfels broke away from the tradition of copying earlier works to make original observations of their own. Bock created his own system of plant classification. Physician Valerius Cordus authored a botanically and pharmacologically important herbal Historia Plantarum in 1544 and a pharmacopoeia of lasting importance, the Dispensatorium
The Orchidaceae are a diverse and widespread family of flowering plants, with blooms that are colourful and fragrant known as the orchid family. Along with the Asteraceae, they are one of the two largest families of flowering plants; the Orchidaceae have about 28,000 accepted species, distributed in about 763 genera. The determination of which family is larger is still under debate, because verified data on the members of such enormous families are continually in flux. Regardless, the number of orchid species nearly equals the number of bony fishes and is more than twice the number of bird species, about four times the number of mammal species; the family encompasses about 6–11% of all seed plants. The largest genera are Bulbophyllum, Epidendrum and Pleurothallis, it includes Vanilla–the genus of the vanilla plant, the type genus Orchis, many cultivated plants such as Phalaenopsis and Cattleya. Moreover, since the introduction of tropical species into cultivation in the 19th century, horticulturists have produced more than 100,000 hybrids and cultivars.
Orchids are distinguished from other plants, as they share some evident, shared derived characteristics, or synapomorphies. Among these are: bilateral symmetry of the flower, many resupinate flowers, a nearly always modified petal, fused stamens and carpels, small seeds. All orchids are perennial herbs, they can grow according to two patterns: Monopodial: The stem grows from a single bud, leaves are added from the apex each year and the stem grows longer accordingly. The stem of orchids with a monopodial growth can reach several metres in length, as in Vanda and Vanilla. Sympodial: Sympodial orchids have a front and a back; the plant produces a series of adjacent shoots, which grow to a certain size and stop growing and are replaced. Sympodial orchids grow laterally following the surface of their support; the growth continues by development of new leads, with their own leaves and roots, sprouting from or next to those of the previous year, as in Cattleya. While a new lead is developing, the rhizome may start its growth again from a so-called'eye', an undeveloped bud, thereby branching.
Sympodial orchids may have visible pseudobulbs joined by a rhizome, which creeps along the top or just beneath the soil. Terrestrial orchids may form corms or tubers; the root caps of terrestrial orchids are white. Some sympodial terrestrial orchids, such as Orchis and Ophrys, have two subterranean tuberous roots. One is used as a food reserve for wintry periods, provides for the development of the other one, from which visible growth develops. In warm and humid climates, many terrestrial orchids do not need pseudobulbs. Epiphytic orchids, those that grow upon a support, have modified aerial roots that can sometimes be a few meters long. In the older parts of the roots, a modified spongy epidermis, called velamen, has the function of absorbing humidity, it can have a silvery-grey, white or brown appearance. In some orchids, the velamen includes spongy and fibrous bodies near the passage cells, called tilosomes; the cells of the root epidermis grow at a right angle to the axis of the root to allow them to get a firm grasp on their support.
Nutrients for epiphytic orchids come from mineral dust, organic detritus, animal droppings and other substances collecting among on their supporting surfaces. The base of the stem of sympodial epiphytes, or in some species the entire stem, may be thickened to form a pseudobulb that contains nutrients and water for drier periods; the pseudobulb has a smooth surface with lengthwise grooves, can have different shapes conical or oblong. Its size is variable; some Dendrobium species have long, canelike pseudobulbs with short, rounded leaves over the whole length. With ageing, the pseudobulb becomes dormant. At this stage, it is called a backbulb. Backbulbs still hold nutrition for the plant, but a pseudobulb takes over, exploiting the last reserves accumulated in the backbulb, which dies off, too. A pseudobulb lives for about five years. Orchids without noticeable pseudobulbs are said to have growths, an individual component of a sympodial plant. Like most monocots, orchids have simple leaves with parallel veins, although some Vanilloideae have reticulate venation.
Leaves may be ovate, lanceolate, or orbiculate, variable in size on the individual plant. Their characteristics are diagnostic, they are alternate on the stem folded lengthwise along the centre, have no stipules. Orchid leaves have siliceous bodies called stegmata in the vascular bundle sheaths and are fibrous; the structure of the leaves corresponds to the specific habitat of the plant. Species that bask in sunlight, or grow on sites which can be very dry, have thick, leathery leaves and the laminae are covered by a waxy cuticle to retain their necessary water supply. Shade-loving species, on the other hand, have thin leaves; the leaves of most orchids are perennial, that is, they live for several years, while others those with plicate leaves as in Catasetum, shed them annually and de
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
Bryophytes are an informal group consisting of three divisions of non-vascular land plants: the liverworts and mosses. They are characteristically limited in size and prefer moist habitats although they can survive in drier environments; the bryophytes consist of about 20,000 plant species. Bryophytes produce enclosed reproductive structures, they reproduce via spores. Bryophytes are considered to be a paraphyletic group and not a monophyletic group, although some studies have produced contrary results. Regardless of their status, the name is convenient and remains in use as an informal collective term; the term "bryophyte" comes from Greek βρύον, bryon "tree-moss, oyster-green" and φυτόν, phyton "plant". The defining features of bryophytes are: Their life cycles are dominated by the gametophyte stage Their sporophytes are unbranched They do not have a true vascular tissue containing lignin Bryophytes exist in a wide variety of habitats, they can be found growing in a range of temperatures and moisture.
Bryophytes can grow where vascularized plants cannot because they do not depend on roots for an uptake of nutrients from soil. Bryophytes can survive on bare soil. Like all land plants, bryophytes have life cycles with alternation of generations. In each cycle, a haploid gametophyte, each of whose cells contains a fixed number of unpaired chromosomes, alternates with a diploid sporophyte, whose cell contain two sets of paired chromosomes. Gametophytes produce haploid sperm and eggs which fuse to form diploid zygotes that grow into sporophytes. Sporophytes produce haploid spores by meiosis. Bryophytes are gametophyte dominant, meaning that the more prominent, longer-lived plant is the haploid gametophyte; the diploid sporophytes appear only and remain attached to and nutritionally dependent on the gametophyte. In bryophytes, the sporophytes produce a single sporangium. Liverworts and hornworts spend most of their lives as gametophytes. Gametangia and antheridia, are produced on the gametophytes, sometimes at the tips of shoots, in the axils of leaves or hidden under thalli.
Some bryophytes, such as the liverwort Marchantia, create elaborate structures to bear the gametangia that are called gametangiophores. Sperm are flagellated and must swim from the antheridia that produce them to archegonia which may be on a different plant. Arthropods can assist in transfer of sperm. Fertilized eggs become zygotes. Mature sporophytes remain attached to the gametophyte, they consist of a stalk called a single sporangium or capsule. Inside the sporangium, haploid spores are produced by meiosis; these are dispersed, most by wind, if they land in a suitable environment can develop into a new gametophyte. Thus bryophytes disperse by a combination of swimming sperm and spores, in a manner similar to lycophytes and other cryptogams; the arrangement of antheridia and archegonia on an individual bryophyte plant is constant within a species, although in some species it may depend on environmental conditions. The main division is between species in which the antheridia and archegonia occur on the same plant and those in which they occur on different plants.
The term monoicous may be used where antheridia and archegonia occur on the same gametophyte and the term dioicous where they occur on different gametophytes. In seed plants, "monoecious" is used where flowers with anthers and flowers with ovules occur on the same sporophyte and "dioecious" where they occur on different sporophytes; these terms may be used instead of "monoicous" and "dioicous" to describe bryophyte gametophytes. "Monoecious" and "monoicous" are both derived from the Greek for "one house", "dioecious" and "dioicous" from the Greek for two houses. The use of the "oicy" terminology is said to have the advantage of emphasizing the difference between the gametophyte sexuality of bryophytes and the sporophyte sexuality of seed plants. Monoicous plants are hermaphroditic, meaning that the same plant has both sexes; the exact arrangement of the antheridia and archegonia in monoicous plants varies. They may be borne on different shoots, on the same shoot but not together in a common structure, or together in a common "inflorescence".
Dioicous plants are unisexual. All four patterns occur in species of the moss genus Bryum. Traditionally, all living land plants without vascular tissues were classified in a single taxonomic group a division. More phylogenetic research has questioned whether the bryophytes form a monophyletic group and thus whether they should form a single taxon. Although a 2005 study supported the traditional view that the bryophytes form a monophyletic group, by 2010 a broad consensus had emerged among systematists that bryophytes as a whole are not a natural group, although each of the three extant groups is monophyletic; the three bryophyte clades are the Marchantiophyta and Anthocerotophyta. The vascular plants or tracheophytes form a fourth, unranked clade of land plants called the "Polysporangiophyta". In this analysis, hornworts are sister
Algae is an informal term for a large, diverse group of photosynthetic eukaryotic organisms that are not closely related, is thus polyphyletic. Including organisms ranging from unicellular microalgae genera, such as Chlorella and the diatoms, to multicellular forms, such as the giant kelp, a large brown alga which may grow up to 50 m in length. Most are aquatic and autotrophic and lack many of the distinct cell and tissue types, such as stomata and phloem, which are found in land plants; the largest and most complex marine algae are called seaweeds, while the most complex freshwater forms are the Charophyta, a division of green algae which includes, for example and the stoneworts. No definition of algae is accepted. One definition is that algae "have chlorophyll as their primary photosynthetic pigment and lack a sterile covering of cells around their reproductive cells". Although cyanobacteria are referred to as "blue-green algae", most authorities exclude all prokaryotes from the definition of algae.
Algae constitute a polyphyletic group since they do not include a common ancestor, although their plastids seem to have a single origin, from cyanobacteria, they were acquired in different ways. Green algae are examples of algae that have primary chloroplasts derived from endosymbiotic cyanobacteria. Diatoms and brown algae are examples of algae with secondary chloroplasts derived from an endosymbiotic red alga. Algae exhibit a wide range of reproductive strategies, from simple asexual cell division to complex forms of sexual reproduction. Algae lack the various structures that characterize land plants, such as the phyllids of bryophytes, rhizoids in nonvascular plants, the roots and other organs found in tracheophytes. Most are phototrophic, although some are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy; some unicellular species of green algae, many golden algae, euglenids and other algae have become heterotrophs, sometimes parasitic, relying on external energy sources and have limited or no photosynthetic apparatus.
Some other heterotrophic organisms, such as the apicomplexans, are derived from cells whose ancestors possessed plastids, but are not traditionally considered as algae. Algae have photosynthetic machinery derived from cyanobacteria that produce oxygen as a by-product of photosynthesis, unlike other photosynthetic bacteria such as purple and green sulfur bacteria. Fossilized filamentous algae from the Vindhya basin have been dated back to 1.6 to 1.7 billion years ago. The singular alga retains that meaning in English; the etymology is obscure. Although some speculate that it is related to Latin algēre, "be cold", no reason is known to associate seaweed with temperature. A more source is alliga, "binding, entwining"; the Ancient Greek word for seaweed was φῦκος, which could mean either the seaweed or a red dye derived from it. The Latinization, fūcus, meant the cosmetic rouge; the etymology is uncertain, but a strong candidate has long been some word related to the Biblical פוך, "paint", a cosmetic eye-shadow used by the ancient Egyptians and other inhabitants of the eastern Mediterranean.
It could be any color: black, green, or blue. Accordingly, the modern study of marine and freshwater algae is called either phycology or algology, depending on whether the Greek or Latin root is used; the name Fucus appears in a number of taxa. The algae contain chloroplasts. Chloroplasts contain circular DNA like that in cyanobacteria and are interpreted as representing reduced endosymbiotic cyanobacteria. However, the exact origin of the chloroplasts is different among separate lineages of algae, reflecting their acquisition during different endosymbiotic events; the table below describes the composition of the three major groups of algae. Their lineage relationships are shown in the figure in the upper right. Many of these groups contain some members; some retain plastids, but not chloroplasts. Phylogeny based on plastid not nucleocytoplasmic genealogy: Linnaeus, in Species Plantarum, the starting point for modern botanical nomenclature, recognized 14 genera of algae, of which only four are considered among algae.
In Systema Naturae, Linnaeus described the genera Volvox and Corallina, a species of Acetabularia, among the animals. In 1768, Samuel Gottlieb Gmelin published the Historia Fucorum, the first work dedicated to marine algae and the first book on marine biology to use the new binomial nomenclature of Linnaeus, it included elaborate illustrations of seaweed and marine algae on folded leaves. W. H. Harvey and Lamouroux were the first to divide macroscopic algae into four divisions based on their pigmentation; this is the first use of a biochemical criterion in plant systematics. Harvey's four divisions are: red algae, brown algae, green algae, Diatomaceae. At this time, microscopic algae were discovered and reported by a different group of workers studying the Infusoria. Unlike macroalgae, which were viewed as plants, microalgae were considered animals because they are motile; the nonmotile microalgae were sometimes seen as stages of the lifecycle of plants, macroalgae, or animals. Although used as a taxonomic category in some pre-D
A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough and sometimes rigid, it provides the cell with both structural support and protection, acts as a filtering mechanism. Cell walls are present in most prokaryotes, in algae and fungi but in other eukaryotes including animals. A major function is to act as pressure vessels, preventing over-expansion of the cell when water enters; the composition of cell walls varies between species and may depend on cell type and developmental stage. The primary cell wall of land plants is composed of the polysaccharides cellulose and pectin. Other polymers such as lignin, suberin or cutin are anchored to or embedded in plant cell walls. Algae possess cell walls made of glycoproteins and polysaccharides such as carrageenan and agar that are absent from land plants. In bacteria, the cell wall is composed of peptidoglycan; the cell walls of archaea have various compositions, may be formed of glycoprotein S-layers, pseudopeptidoglycan, or polysaccharides.
Fungi possess cell walls made of the N-acetylglucosamine polymer chitin. Unusually, diatoms have a cell wall composed of biogenic silica. A plant cell wall was first observed and named by Robert Hooke in 1665. However, "the dead excrusion product of the living protoplast" was forgotten, for three centuries, being the subject of scientific interest as a resource for industrial processing or in relation to animal or human health. In 1804, Karl Rudolphi and J. H. F. Link proved. Before, it had been thought that fluid passed between them this way; the mode of formation of the cell wall was controversial in the 19th century. Hugo von Mohl advocated the idea. Carl Nägeli believed that the growth of the wall in thickness and in area was due to a process termed intussusception; each theory was improved in the following decades: the apposition theory by Eduard Strasburger, the intussusception theory by Julius Wiesner. In 1930, Ernst Münch coined the term apoplast in order to separate the "living" symplast from the "dead" plant region, the latter of which included the cell wall.
By the 1980s, some authors suggested replacing the term "cell wall" as it was used for plants, with the more precise term "extracellular matrix", as used for animal cells, but others preferred the older term. Cell walls serve similar purposes in those organisms, they may give cells offering protection against mechanical stress. In multicellular organisms, they permit the organism to hold a definite shape. Cell walls limit the entry of large molecules that may be toxic to the cell, they further permit the creation of stable osmotic environments by preventing osmotic lysis and helping to retain water. Their composition and form may change during the cell cycle and depend on growth conditions. In most cells, the cell wall is flexible, meaning that it will bend rather than holding a fixed shape, but has considerable tensile strength; the apparent rigidity of primary plant tissues is enabled by cell walls, but is not due to the walls' stiffness. Hydraulic turgor pressure creates this rigidity, along with the wall structure.
The flexibility of the cell walls is seen when plants wilt, so that the stems and leaves begin to droop, or in seaweeds that bend in water currents. As John Howland explains Think of the cell wall as a wicker basket in which a balloon has been inflated so that it exerts pressure from the inside; such a basket is rigid and resistant to mechanical damage. Thus does the prokaryote cell gain strength from a flexible plasma membrane pressing against a rigid cell wall; the apparent rigidity of the cell wall thus results from inflation of the cell contained within. This inflation is a result of the passive uptake of water. In plants, a secondary cell wall is a thicker additional layer of cellulose which increases wall rigidity. Additional layers may be formed by suberin in cork cell walls; these compounds are rigid and waterproof. Both wood and bark cells of trees have secondary walls. Other parts of plants such as the leaf stalk may acquire similar reinforcement to resist the strain of physical forces.
The primary cell wall of most plant cells is permeable to small molecules including small proteins, with size exclusion estimated to be 30-60 kDa. The pH is an important factor governing the transport of molecules through cell walls. Cell walls evolved independently including within the photosynthetic eukaryotes. In these lineages, the cell wall is related to the evolution of multicellularity, terrestrialization and vascularization; the walls of plant cells must have sufficient tensile strength to withstand internal osmotic pressures of several times atmospheric pressure that result from the difference in solute concentration between the cell interior and external solutions. Plant cell walls vary from 0.1 to several µm in thickness. Up to three strata or layers may be found in plant cell walls: The primary cell wall a thin and extensible layer formed while the cell is growing; the secondary cell wall, a thick layer formed inside the primary cell wall after the cell is grown. It is not found in all cell types.
Some cells, such as the conducting cells in xylem, possess a secondary wall containing lignin, which strengthens and waterproofs the wall. The middle lamella, a layer rich in pectins; this outermost layer
Gynoecium is most used as a collective term for the parts of a flower that produce ovules and develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; the gynoecium is referred to as the "female" portion of the flower, although rather than directly producing female gametes, the gynoecium produces megaspores, each of which develops into a female gametophyte which produces egg cells. The term gynoecium is used by botanists to refer to a cluster of archegonia and any associated modified leaves or stems present on a gametophyte shoot in mosses and hornworts; the corresponding terms for the male parts of those plants are clusters of antheridia within the androecium. Flowers that bear a gynoecium but no stamens are called carpellate. Flowers lacking a gynoecium are called staminate; the gynoecium is referred to as female because it gives rise to female gametophytes. Gynoecium development and arrangement is important in systematic research and identification of angiosperms, but can be the most challenging of the floral parts to interpret.
The gynoecium may consist of one or more separate pistils. A pistil consists of an expanded basal portion called the ovary, an elongated section called a style and an apical structure that receives pollen called a stigma; the ovary, is the enlarged basal portion which contains placentas, ridges of tissue bearing one or more ovules. The placentas and/or ovule may be born on the gynoecial appendages or less on the floral apex; the chamber in which the ovules develop is called a locule. The style, is a pillar-like stalk; some flowers such as Tulipa do not have a distinct style, the stigma sits directly on the ovary. The style is a hollow tube in some plants such as lilies, or has transmitting tissue through which the pollen tubes grow; the stigma, is found at the tip of the style, the portion of the carpel that receives pollen. It is sticky or feathery to capture pollen; the word "pistil" comes from Latin pistillum meaning pestle. A sterile pistil in a male flower is referred to as a pistillode; the pistils of a flower are considered to be composed of carpels.
A carpel is the female reproductive part of the flower, interpreted as modified leaves bearing structures called ovules, inside which the egg cells form. A pistil may consist of one carpel, with its ovary and stigma, or several carpels may be joined together with a single ovary, the whole unit called a pistil; the gynoecium may consist of one multi-carpellate pistil. The number of carpels is described by terms such as tricarpellate. Carpels are thought to be phylogenetically derived from ovule-bearing leaves or leaf homologues, which evolved to form a closed structure containing the ovules; this structure is rolled and fused along the margin. Although many flowers satisfy the above definition of a carpel, there are flowers that do not have carpels according to this definition because in these flowers the ovule, although enclosed, are borne directly on the shoot apex, only become enclosed by the carpel. Different remedies have been suggested for this problem. An easy remedy that applies to most cases is to redefine the carpel as an appendage that encloses ovule and may or may not bear them.
If a gynoecium has a single carpel, it is called monocarpous. If a gynoecium has multiple, distinct carpels, it is apocarpous. If a gynoecium has multiple carpels "fused" into a single structure, it is syncarpous. A syncarpous gynoecium can sometimes appear much like a monocarpous gynoecium; the degree of connation in a syncarpous gynoecium can vary. The carpels retain separate styles and stigmas; the carpels may be "fused" except for retaining separate stigmas. Sometimes carpels possess distinct ovaries. In a syncarpous gynoecium, the "fused" ovaries of the constituent carpels may be referred to collectively as a single compound ovary, it can be a challenge to determine. If the styles and stigmas are distinct, they can be counted to determine the number of carpels. Within the compound ovary, the carpels may have distinct locules divided by walls called septa. If a syncarpous gynoecium has a single style and stigma and a single locule in the ovary, it may be necessary to examine how the ovules are attached.
Each carpel will have a distinct line of placentation where the ovules are attached. Pistils begin as small primordia on a floral apical meristem, forming than, closer to the apex than sepal and stamen primordia. Morphological and molecular studies of pistil ontogeny reveal that carpels are most homologous to leaves. A carpel has a similar function to a megasporophyll, but includes a stigma, is fused, with ovules enclosed in the enlarged lower portion, the ovary. In some basal angiosperm lineages and Winteraceae, a carpel begins as a shallow cup where the ovules de