In vascular plants, the root is the organ of a plant that lies below the surface of the soil. Roots can be aerial or aerating, that is, growing up above the ground or above water. Furthermore, a stem occurring below ground is not exceptional either. Therefore, the root is best defined as the non-nodes bearing parts of the plant's body. However, important internal structural differences between stems and roots exist; the fossil record of roots—or rather, infilled voids where roots rotted after death—spans back to the late Silurian, about 430 million years ago. Their identification is difficult, because casts and molds of roots are so similar in appearance to animal burrows, they can be discriminated using a range of features. The first root that comes from a plant is called the radicle. A root's four major functions are: absorption of inorganic nutrients. In response to the concentration of nutrients, roots synthesise cytokinin, which acts as a signal as to how fast the shoots can grow. Roots function in storage of food and nutrients.
The roots of most vascular plant species enter into symbiosis with certain fungi to form mycorrhizae, a large range of other organisms including bacteria closely associate with roots. When dissected, the arrangement of the cells in a root is root hair, epiblem, endodermis, pericycle and, the vascular tissue in the centre of a root to transport the water absorbed by the root to other places of the plant; the most striking characteristic of roots is that, roots have an endogenous origin, i.e. it originates and develops from an inner layer of the mother axis. Whereas Stem-branching and leaves are exogenous, i.e. start to develop from the cortex, an outer layer. In its simplest form, the term root architecture refers to the spatial configuration of a plant’s root system; this system can be complex and is dependent upon multiple factors such as the species of the plant itself, the composition of the soil and the availability of nutrients. The configuration of root systems serves to structurally support the plant, compete with other plants and for uptake of nutrients from the soil.
Roots grow to specific conditions. For example, a root system that has developed in dry soil may not be as efficient in flooded soil, yet plants are able to adapt to other changes in the environment, such as seasonal changes. Root architecture plays the important role of providing a secure supply of nutrients and water as well as anchorage and support; the main terms used to classify the architecture of a root system are: Branch magnitude: the number of links. Topology: the pattern of branching, including:Herringbone: alternate lateral branching off a parent root Dichotomous: opposite, forked branches Radial: whorl of branches around a rootLink length: the distance between branches. Root angle: the radial angle of a lateral root’s base around the parent root’s circumference, the angle of a lateral root from its parent root, the angle an entire system spreads. Link radius: the diameter of a root. All components of the root architecture are regulated through a complex interaction between genetic responses and responses due to environmental stimuli.
These developmental stimuli are categorised as intrinsic, the genetic and nutritional influences, or extrinsic, the environmental influences and are interpreted by signal transduction pathways. The extrinsic factors that affect root architecture include gravity, light exposure and oxygen, as well as the availability or lack of nitrogen, sulphur and sodium chloride; the main hormones and respective pathways responsible for root architecture development include: Auxin – Auxin promotes root initiation, root emergence and primary root elongation. Cytokinins – Cytokinins regulate root apical meristem size and promote lateral root elongation. Gibberellins -- Together with ethylene they promote elongation. Together with auxin they promote root elongation. Gibberellins inhibit lateral root primordia initiation. Ethylene – Ethylene promotes crown root formation. Early root growth is one of the functions of the apical meristem located near the tip of the root; the meristem cells more or less continuously divide, producing more meristem, root cap cells, undifferentiated root cells.
The latter become the primary tissues of the root, first undergoing elongation, a process that pushes the root tip forward in the growing medium. These cells differentiate and mature into specialized cells of the root tissues. Growth from apical meristems is known as primary growth. Secondary growth encompasses all growth in diameter, a major component of woody plant tissues and many nonwoody plants. For example, storage roots of sweet potato are not woody. Secondary growth occurs at the lateral meristems, namely the vascular cork cambium; the former forms secondary phloem, while the latter forms the periderm. In plants with secondary growth, the vascular cambium, originating between the xylem and the phloem, forms a cylinder of tissue along the stem and root; the vascular cambium forms new cells on both the inside and outside of the cambium cylinder, with those on the inside forming secondary xylem cells, those on the outside forming secondary phloem cells. As
In botany, the petiole is the stalk that attaches the leaf blade to the stem. Outgrowths appearing on each side of the petiole in some species are called stipules. Leaves lacking a petiole are called epetiolate; the petiole is a stalk. In petiolate leaves, the leaf stalk may be long, as in the leaves of celery and rhubarb, short or absent, in which case the blade attaches directly to the stem and is said to be sessile. Subpetiolate leaves are nearly petiolate, or have an short petiole, may appear sessile; the broomrape family Orobanchaceae is an example of a family. In some other plant groups, such as the speedwell genus Veronica and sessile leaves may occur in different species. In the grasses the leaves are apetiolate, but the leaf blade may be narrowed at the junction with the leaf sheath to form a pseudopetiole, as in Pseudosasa japonica. In plants with compound leaves, the leaflets are attached to a continuation of the petiole called the rachis; each leaflet may be attached to the rachis by a short stalk called the petiolule.
There may be swollen regions at either end of the petiole known as pulvina that are composed of a flexible tissue that allows leaf movement. Pulvina are common in the prayer plant family Marantaceae. A pulvinus on a petiolule is called a pulvinulus. In some plants, the petioles are flattened and widened, to become phyllodes or phyllodia, or cladophylls and the true leaves may be reduced or absent. Thus, the phyllode comes to serve the functions of the leaf. Phyllodes are common in the genus Acacia the Australian species, at one time put in Acacia subgenus Phyllodineae. In Acacia koa, the phyllodes are leathery and thick, allowing the tree to survive stressful environments; the petiole allows submerged hydrophytes to have leaves floating at different depths, the petiole being between the node and the stem. In plants such as rhubarb, celery and cardoons the petioles are cultivated as edible crops; the petiole of rhubarb produces the leaf at its end. Botanically it is culinarily used as a fruit. Petiole comes from Latin petiolus, or peciolus "little foot", "stem", an alternative diminutive of pes "foot".
The regular diminutive pediculus is used for "foot stalk". Hyponastic response Pedicel "Petiole". Collier's New Encyclopedia. 1921
Phytochemistry is the study of phytochemicals, which are chemicals derived from plants. Those studying phytochemistry strive to describe the structures of the large number of secondary metabolic compounds found in plants, the functions of these compounds in human and plant biology, the biosynthesis of these compounds. Plants synthesize phytochemicals for many reasons, including to protect themselves against insect attacks and plant diseases. Phytochemicals in food plants are active in human biology, in many cases have health benefits; the compounds found in plants are of many kinds, but most are in four major biochemical classes, the alkaloids, glycosides and terpenes. Phytochemistry can be considered sub-fields of chemistry. Activities can be led in the wild with the aid of ethnobotany; the applications of the discipline can be for pharmacognosy, or the discovery of new drugs, or as an aid for plant physiology studies. Techniques used in the field of phytochemistry are extraction and structural elucidation of natural products, as well as various chromatography techniques.
The list of simple elements of which plants are constructed—carbon, hydrogen, phosphorus, etc.—is not different from similar lists for animals, fungi, or bacteria. The fundamental atomic components of plants are the same as for all life. Phytochemistry is used in the field of Chinese medicine in the field of herbal medicine. Phytochemical technique applies to the quality control of Chinese medicine, Ayurvedic medicine or herbal medicine of various chemical components, such as saponins, volatile oils and anthraquinones. In the development of rapid and reproducible analytical techniques, the combination of HPLC with different detectors, such as diode array detector, refractive index detector, evaporative light scattering detector and mass spectrometric detector, has been developed. In most cases, biologically active compounds in Chinese medicine, Ayurveda, or herbal medicine have not been determined. Therefore, it is important to use the phytochemical methods to screen and analyze bioactive components, not only for the quality control of crude drugs, but for the elucidation of their therapeutic mechanisms.
Modern pharmacological studies indicate that binding to receptors or ion channels on cell membranes is the first step of some drug actions. A new method in phytochemistry called biochromatography has been developed; this method combines human red cell membrane extraction and high performance liquid chromatography to screen potential active components in Chinese medicine. Many plants produce chemical compounds for defence against herbivores; these are useful as drugs, the content and known pharmacological activity of these substances in medicinal plants is the scientific basis for their use. The major classes of pharmacologically active phytochemicals are described below, with examples of medicinal plants that contain them. Human settlements are surrounded by weeds useful as medicines, such as nettle and chickweed. Many phytochemicals, including curcumin, epigallocatechin gallate and resveratrol are pan-assay interference compounds and are not useful in drug discovery. Alkaloids are bitter-tasting chemicals widespread in nature, toxic.
There are several classes with different modes of action as drugs, both recreational and pharmaceutical. Medicines of different classes include atropine and hyoscyamine, the traditional medicine berberine, cocaine, morphine, reserpine and quinine, vincristine. Anthraquinone glycosides are found in the laxatives senna and Aloe; the cardiac glycosides are powerful drugs from plants including lily of the valley. They include digoxin and digitoxin which support the beating of the heart, act as diuretics. Polyphenols of several classes are widespread in plants, they include the colourful anthocyanins, hormone-mimicking phytoestrogens, astringent tannins. In Ayurveda, the astringent rind of the pomegranate is used as a medicine, while polyphenol extracts from plant materials such as grape seeds are sold for their potential health benefits They have been continually studied in cell cultures for their different anti-cancer effects. Plants containing phytoestrogens have been used for centuries to treat gynaecological disorders such as fertility and menopausal problems.
Among these plants are Pueraria mirifica, angelica and anise. Terpenes and terpenoids of many kinds are found in resinous plants such as the conifers, they are aromatic and serve to repel herbivores. Their scent makes them useful in essential oils, whether for perfumes such as rose and lavender, or for aromatherapy; some have had medicinal uses: thymol is an antiseptic and was once used as a vermifuge. Tropical Botanical Garden and Research Institute UBC Botanical Garden and Centre for Plant Research
Opuntia called prickly pear, is a genus in the cactus family, Cactaceae. Prickly pears are known as tuna, nopal from the Nahuatl word nōpalli for the pads, or nostle, from the Nahuatl word nōchtli for the fruit; the genus is named for the Ancient Greek city of Opus, according to Theophrastus, an edible plant grew and could be propagated by rooting its leaves. The most common culinary species is the Indian fig opuntia. O. ficus-indica is a large trunk-forming segmented cactus which may grow to 5–7 metres with a crown of 3 metres in diameter and a trunk diameter of 1 metre. Cladodes may be spineless. Prickly pears grow with flat, rounded cladodes containing large, fixed spines and small, hairlike prickles called glochids that adhere to skin or hair detach from the plant; the flowers are large, solitary and epiperigynous, with a perianth consisting of distinct, spirally arranged tepals and a hypanthium. The stamens are numerous and in spiral or whorled clusters, the gynoecium has numerous inferior ovaries per carpel.
Placentation is parietal, the fruit is a berry with arillate seeds. Prickly pear species can vary in habit. O. ficus-indica thrives in regions with mild winters having a prolonged dry spell followed by hot summers with occasional rain and low humidity. A mean annual rainfall of 350–500 millimetres provides good growth rates. O. ficus-indica proliferates in various soils ranging from sub-acid to sub-alkaline, with clay content not exceeding 15-20% and the soil well-drained. The shallow root system enables the plant to grow in shallow, loose soils, such as on mountain slopes. Opuntia spreads into large clonal colonies, which contribute to its being considered a noxious weed in some places. Animals that eat Opuntia include Cyclura rock iguanas; the fruit are relished by many arid land animals, chiefly birds, which thus help distribute the seeds. Opuntia pathogens include the sac fungus Sammons' Opuntia virus; the ant Crematogaster opuntiae and the spider Theridion opuntia are named because of their association with prickly pear cacti.
Like most true cactus species, prickly pears are native only to the Americas. Through human actions, they have since been introduced to many other areas of the world. Prickly pear species are found in abundance in Mexico in the central and western regions, in the Caribbean islands. In the United States, prickly pears are native to many areas of the arid, semi-arid, drought-prone Western and South Central United States, including the lower elevations of the Rocky Mountains and southern Great Plains, where species such as Opuntia phaeacantha and Opuntia polyacantha become dominant, to the desert Southwest, where several types are endemic. Prickly pear cactus is native to sandy coastal beach scrub environments of the East Coast from Florida to southern Connecticut. Opuntia species are the most cold-tolerant of the lowland cacti, extending into western and southern Canada. Prickly pears produce a fruit eaten in Mexico and in the Mediterranean region, known as tuna; the fruit can be wine-red, green, or yellow-orange.
In the Galápagos Islands, six different species are found: O. echios, O. galapageia, O. helleri, O. insularis, O. saxicola, O. megasperma. These species are divided into 14 different varieties. For this reason, they have been described as "an excellent example of adaptive radiation". On the whole, islands with tall, trunked varieties have giant tortoises, islands lacking tortoises have low or prostrate forms of Opuntia. Prickly pears are a prime source of food for the common giant tortoises in the Galápagos islands so they are important in the food web. Charles Darwin was the first to note that these cacti have thigmotactic anthers: when the anthers are touched, they curl over, depositing their pollen; this movement can be seen by poking the anthers of an open Opuntia flower. The same trait has evolved convergently in other cacti; the first introduction of prickly pears into Australia is ascribed to Governor Philip and the earliest colonists in 1788. Brought from Brazil to Sydney, prickly pear grew in Sydney, New South Wales, where they were rediscovered in a farmer's garden in 1839.
They appear to have spread from New South Wales and caused great ecological damage in the eastern states. They are found in the Mediterranean region of Northern Africa in Tunisia, where they grow all over the countryside, in parts of southern Europe Spain, where they grow in the east, south-east and south of the country, in Malta, where they grow all over the islands, they can be found in enormous numbers in parts of South Africa, where they were introduced from South America. Prickly pears are considered an invasive species in Australia, South Africa, Hawaii, among other locations. Prickly pears were imported into Europe during the 1500s and Australia in the 18th century for gardens, were used as a natural agricultural fencing and in an attempt to establish a cochineal dye industry. They
Fouquieria is a genus of 11 species of desert plants, the sole genus in the family Fouquieriaceae. The genus includes the boojum tree or cirio, they have semisucculent stems with thinner spikes projecting from them, with leaves on the bases spikes. They do not look much like them; these plants are native to northern Mexico and the bordering US states of Arizona, southern California, New Mexico, parts of southwestern Texas, favoring low, arid hillsides. The Seri people identify three species of Fouquieria in their area of Mexico: jomjéeziz or xomjéeziz, jomjéeziz caacöl, cototaj; the genus is named after French physician Pierre Fouquier. The spines of Fouquieria develop in an unusual way, from a woody thickening on the outer side of the leaf petiole, which remains after the leaf blade and most of the petiole separate and fall from the plant. Fouquieria species do not have a close resemblance to any other sort of plants. Prior to this, they had been variously placed in their own order, Fouquieriales.
Fouquieria shrevei is endemic to the Cuatro Ciénegas basin in Mexico, is unusual in possessing vertical resinous wax bands on the stems, exhibits gypsophily, the ability to grow on soils with a high concentration of gypsum. It is presumed to be moth-pollinated. Other species in the genus with orange or red flowers are pollinated by hummingbirds or carpenter bees. Fouquieria diguetii is host to a peacock mite, Tuckerella eloisae. Moser, Mary B.. Comcáac quih yaza quih hant ihíip hac: Diccionario seri-español-inglés. Hermosillo, Sonora: Universidad de Sonora and Plaza y Valdés Editores; the Fouquieria Page at the National University of Mexico with photos of the species in the wild Fouquieriaceae in L. Watson and M. J. Dallwitz; the families of flowering plants
Phoenix is a genus of 14 species of palms, native to an area starting from the Canary Islands in the west, across northern and central Africa, to the extreme southeast of Europe, continuing throughout southern Asia from Turkey east to southern China and Malaysia. The diverse habitats they occupy include swamps and mangrove sea coasts. Most Phoenix species originate in semiarid regions, but occur near high groundwater levels, rivers, or springs; the genus is unusual among members of subfamily Coryphoideae in having pinnate, rather than palmate leaves. The palms were more widespread in the past than they are at present; some Phoenix palms have become naturalised in other parts of the world. The generic name derives from φοῖνιξ or φοίνικος, the Greek word for the date palm used by Theophrastus and Pliny the Elder, it most referred to either the Phoenicians. This genus is medium to robust in size, but includes a few dwarf species. Many of the trunked species do not form above-ground stems for several years.
The pinnate leaves, 1–6 m long, all share the common feature of metamorphosed lower-leaf segments into long, vicious spines. The leaves have short or absent petioles and possess the rare feature among pinnate palms of induplicate leaflets; the plants are dioecious, with male and female flowers on separate plants. The flowers are inconspicuous yellowish-brown and about 1 cm wide, but grouped on conspicuous large multibranched panicles 30–90 cm long; the inflorescence emerges from a boat-shaped, leathery bract, forming large, pendent clusters. Phoenix fruit develops from one carpel as a berry, 1–7 cm long, yellow to red-brown or dark purple when mature, with one elongated grooved seed. A majority of the forest palms grow under the shade of dominating forests trees along fragile hill slopes and stream courses in warm, humid conditions; the palms are found growing on a wide variety of soils extending to degraded forest margins in grasslands. In the tropics, most are found below 1250 m altitude. Branching of the aerial trunk is rare and is induced by injury to the terminal growing bud.
Flowering and fruit are annual. The reproduction is by vegetative multiplication. Many species of Phoenix produce vegetative offshoots called bulbils from basal portions of their stems which, on rooting, develop new saplings. Close relationship among the 14 species is illustrated by the ease of hybridisation and cross-pollination. Several natural hybrids were hence obtained: P. dactylifera × P. sylvestris, P. dactylifera × P. canariensis, P. dactylifera × P. reclinata. Phoenix species are used as food plants by the larvae of some Lepidoptera species, including Paysandisia archon and the Batrachedra species B. amydraula, B. arenosella and B. isochtha. The fruit of P. dactylifera, the date of commerce, is large with a thick layer of fruit pulp, edible sweet and rich in sugar. The central soft part of the stem of P. rupicola, P. acaulis, P. humilis is a rich source of starch. Palms are felled to extract this central ‘pith’, dried, powdered and used for preparation of bread by Indian natives; the P. canariensis sap is cooked to a thick syrup.
P. sylvestris Roxb. is used in India as a source of sugar. The sugary sap from some African palms yields country liquor on fermentation. While P. dactylifera is grown for its edible dates, the Canary Island date palm and pygmy date palm are grown as ornamental plants, but their dates are used as food for livestock and poultry. The Canary Island date palm differs from the date palm in having a stouter trunk, more leaves to the crown, more spaced leaflets, deep green rather than grey-green leaves; the fruit of P. canariensis is edible, but eaten by humans because of their small size and thin flesh. The different species of the genus hybridise where they grow in proximity; this can be a problem when planting P. canariensis as an ornamental plant, as the hybrid palms are aesthetically inferior and do not match the pure-bred plants when planted in avenues, etc. Phoenix acaulis Roxb. – dwarf date palm – Himalayas Phoenix andamanensis S. C. Barrow – Andaman Islands Phoenix atlantica A. Chev. Cape Verde palm, endemic to the Cape Verde Islands, erroneously characterized as a feral P. dactylifera Phoenix caespitosa Chiov.
– Djibouti, Saudi Arabia, Oman Phoenix canariensis Chabaud – Canary Island date palm – native to Canary Islands, naturalized in Spain, Australia, Bermuda Phoenix dactylifera L. – date palm – native to southwestern Asia, naturalized in Spain, Madeira and western Africa, Mauritius, Réunion, India, Fiji, New Caledonia, Baja California, Sonora, El Salvador, Caribbean Phoenix loureiroi Kunth – China, Himalayas, Philippines Phoenix paludosa Roxb. – mangrove date palm – Indian Subcontinent, Sumatra, Andaman & Nicobar Islands Phoenix pusilla Gaertn. – Ceylon date palm – Ind
A cactus is a member of the plant family Cactaceae, a family comprising about 127 genera with some 1750 known species of the order Caryophyllales. The word "cactus" derives, through Latin, from the Ancient Greek κάκτος, kaktos, a name used by Theophrastus for a spiny plant whose identity is not certain. Cacti occur in a wide range of sizes. Most cacti live in habitats subject to at least some drought. Many live in dry environments being found in the Atacama Desert, one of the driest places on earth. Cacti show many adaptations to conserve water. All cacti are succulents, meaning they have thickened, fleshy parts adapted to store water. Unlike many other succulents, the stem is the only part of most cacti where this vital process takes place. Most species of cacti have lost true leaves, retaining only spines, which are modified leaves; as well as defending against herbivores, spines help prevent water loss by reducing air flow close to the cactus and providing some shade. In the absence of leaves, enlarged stems carry out photosynthesis.
Cacti are native to the Americas, ranging from Patagonia in the south to parts of western Canada in the north—except for Rhipsalis baccifera, which grows in Africa and Sri Lanka. Cactus spines are produced from specialized structures called areoles, a kind of reduced branch. Areoles are an identifying feature of cacti; as well as spines, areoles give rise to flowers, which are tubular and multipetaled. Many cacti have short growing seasons and long dormancies, are able to react to any rainfall, helped by an extensive but shallow root system that absorbs any water reaching the ground surface. Cactus stems are ribbed or fluted, which allows them to expand and contract for quick water absorption after rain, followed by long drought periods. Like other succulent plants, most cacti employ a special mechanism called "crassulacean acid metabolism" as part of photosynthesis. Transpiration, during which carbon dioxide enters the plant and water escapes, does not take place during the day at the same time as photosynthesis, but instead occurs at night.
The plant stores the carbon dioxide it takes in as malic acid, retaining it until daylight returns, only using it in photosynthesis. Because transpiration takes place during the cooler, more humid night hours, water loss is reduced. Many smaller cacti have globe-shaped stems, combining the highest possible volume for water storage, with the lowest possible surface area for water loss from transpiration; the tallest free-standing cactus is Pachycereus pringlei, with a maximum recorded height of 19.2 m, the smallest is Blossfeldia liliputiana, only about 1 cm in diameter at maturity. A grown saguaro is said to be able to absorb as much as 200 U. S. gallons of water during a rainstorm. A few species differ in appearance from most of the family. At least superficially, plants of the genus Pereskia resemble other trees and shrubs growing around them, they have persistent leaves, when older, bark-covered stems. Their areoles identify them as cacti, in spite of their appearance, too, have many adaptations for water conservation.
Pereskia is considered close to the ancestral species from. In tropical regions, other cacti grow as forest epiphytes, their stems are flattened leaf-like in appearance, with fewer or no spines, such as the well-known Christmas cactus or Thanksgiving cactus. Cacti have a variety of uses: many species are used as ornamental plants, others are grown for fodder or forage, others for food. Cochineal is the product of an insect. Many succulent plants in both the Old and New World – such as some Euphorbiaceae – bear a striking resemblance to cacti, may incorrectly be called "cactus" in common usage; the 1,500 to 1,800 species of cacti fall into one of two groups of "core cacti": opuntias and "cactoids". Most members of these two groups are recognizable as cacti, they have fleshy succulent stems. They have small, or transient leaves, they have flowers with ovaries that lie below the sepals and petals deeply sunken into a fleshy receptacle. All cacti have areoles—highly specialized short shoots with short internodes that produce spines, normal shoots, flowers.
The remaining cacti fall into only two genera and Maihuenia, are rather different, which means any description of cacti as a whole must make exceptions for them. Pereskia species superficially resemble other tropical forest trees; when mature, they have woody stems that may be covered with bark and long-lasting leaves that provide the main means of photosynthesis. Their flowers may have superior ovaries, areoles that produce further leaves; the two species of Maihuenia have globe-shaped bodies with prominent leaves at the top. Cacti show a wide variety of growth habits, which are difficult to divide into clear, simple categories. Arborescent cactiThey can be tree-like, meaning they have a single more-or-less woody trunk topped by several to many branches. In the genus Pereskia, the branches are covered with leaves, so the species of this genus may not be recognized as cacti. In most other cacti, the branches are more cactus-like, bare of leaves and bark, cov