Hawkweed
Hawkweed     Hawkweed (Hieracium spp.) often forms dense colonies in areas of the lawn where the soil is infertile and acidic. A hardy perennial found throughout North America, hawkweed holds its rosettes of wildly hairy leaves close to the soil surface, safe from mower blades. Orange hawkweed (Hieracium aurantiacum) and meadow hawkweed (Hieracium pratens) are invasive forms that send up orange or yellow, respectively, dandelion-like flowers on 12-inch-tall leafless stalks. Established plants send out shallow bud-bearing stolons, which form new plants. Dig colonies in spring, and promptly repair the spot with seed or sod. Apply lime if the soil's pH is below 5.5. Sites infested with hawkweed benefit from organic fertilizers, which help the turf grass grow stronger and crowd out the hawkweed.   Weed Control Techniques   Digging. Weeds that regrow from persistent roots must be dug. Use a spade or digging fork to dig spreading perennials, such as bindweed, Canada thistle, and quackgrass. Start digging a foot away from the plant's center to loosen the soil. Then lift the weed from beneath, which reduces how many root pieces are likely to break off and regrow. Dandelion, dock, and other weeds that grow from persistent taproots can be dug the same way, or you can use a special fork-like tool called a dandelion weeder to pry them up. Dig very large taproots that are difficult to pry loose. In lawns and other places where digging dandelions is not practical, use a sharp knife to slice off the leaves and the top inch or two of taproot at a diagonal angle. Some weeds that are easily pulled when the soil is moist must be dug from dry soil.   Crowding plants. When plants grow so close together that the ground between them is shaded, sun-seeking weeds, such as pigweed and purslane, don't have a chance. Use double rows rather than single ones whenever possible in your vegetable garden. In flower beds, place flowers in closely spaced groups. As plants need more room to grow, thin them gradually so weeds get only a fleeting chance at good light. Plants with broad leaves, such as squash and cabbage, do a good job of crowding out weeds. Vigorous lawn grasses that form a tight turf naturally crowd out weeds. To keep turf tight, apply a slow-release organic fertilizer during your lawn's most active season of new growth. The recommended cutting height varies with different species of grass, but with any type of grass it's a good weed-preventive strategy to mow high and often. Long blades of grass often do a good job of shading out germinating weed seeds.           منبع: مرکز مقالات کشاورزی AKE( بزرگترین وبلاگ کشاورزی ایران )         Henbit     Henbit (Lamium amplexicaule) is a mint cousin that's common in gardens in the eastern half of the United States. In the north it is a spring annual. In the south, henbit sprouts in fall and blooms in early spring. The pretty pink flowers are attractive, but the spreading plants will take over a lawn or garden. Mulch discourages this weed, which needs sun to sprout and grow. Henbit is easily controlled by pulling. When cultivating soil infested with henbit, rake out the plants to keep them from rerooting.   Weed Control Techniques   Mulching. Mulch that's more than 2 inches thick can deprive most weed seeds of the light they need to germinate and grow. In vegetable and flower gardens, you can mulch with wheat straw (which has fewer weed seeds than hay), chopped leaves, grass clippings, or many other organic materials. Where weeds are numerous, try covering the soil with four to six sheets of newspaper. Then cover the newspapers with 2 to 3 inches of organic mulch. Pieces of scrap carpeting make a good weed-suppressing mulch to use in pathways between rows. When mulching beneath shrubs and trees, place a sheet of landscape fabric over the soil, then cover it with 3 inches of organic mulch. An edging (a 4- to 6-inch-wide strip of rot-proof material driven into the ground vertically) of brick, stone, or metal will help the mulch stay put, halt invasion by creeping weeds, and make the bed look neat and well groomed.   Pulling. Most young weeds can be pulled from the soil. They will slide out most easily if you pull them when the soil is wet. Getting the root up is crucial, so think of the main stem as the root's handle, and grasp it as close to the soil line as you can. If you find that the weeds are breaking off at the crown as you pull, slip a kitchen fork, dandelion weeder, or similar tool under the weed, and pry and twist as you pull it up. Weeds that have taproots, such as dandelion and plantain, usually must be pried out. A flexible pair of waterproof gloves will keep your hands comfortable as you weed, and it's good to have a nice sitting pad, too. Let pulled weeds bake in the sun for a day or so before composting them. If pulled weeds are holding mature seeds, compost them separately in a hot, moist pile before using this compost in the garden.     Cultivating. Slicing and dicing weeds with a hoe works best when the soil is relatively dry, and the same goes for cultivating with a tiller. With their tops mangled and roots cut, most young weeds will quickly shrivel up and die. Be careful to cultivate only the top inch or two of soil or you may injure nearby garden plant roots and drag new weed seeds to the surface. A sharp hoe works much better than a dull one, so refresh the edge on your hoe with a steel file between weeding sessions. After using either a hoe or tiller to cultivate weeds, go back the next day to nip out any survivors. When battling perennial weeds, you can weaken the plants by chopping them down with a sharp hoe, but it's best to combine hoeing with digging to achieve good control. Never use a tiller in soil that is infested with bindweed, quackgrass, or other weeds that regrow from small pieces of root; they are easily spread by rototilling.           منبع: مرکز مقالات کشاورزی AKE( بزرگترین وبلاگ کشاورزی ایران )         Hop Clover   Hop clover (Trifolium dubium) seeds that find their way into dormant warm-season lawns quietly grow into sturdy rosettes during the winter months. In spring, stems studded with classic three-leaf clovers (and the occasional four-leaf version) lengthen and produce small yellow flower clusters. Use a sharp knife to cut plants off at the soil line to reduce reseeding. The root system left behind will not grow, but will add to the soil's supply of nitrogen as it decomposes. In mild winter climates, pull seedlings when you see them in the lawn during the winter months.   Weed Control Techniques   Reducing reseeding. Most weeds reproduce primarily from seeds, and the seeds of some weeds can remain viable when buried in the soil for decades. So it's essential to keep weeds from shedding seeds in the garden. Garden weeds that are neglected until they reach seed-bearing age can be lopped off near the soil line with pruning shears, a stout knife, or a string trimmer with a blade attachment. Cutting back perennial weeds again and again not only reduces reseeding, it also forces the plants to use up food reserves stored in their roots. In a garden that has gone hopelessly weedy, mowing it down promptly, raking out the seed-bearing debris, and starting over next year is a big step in the right direction. Mowing regularly helps keep weeds under control in lawns. When mowing lawns where seed-bearing weeds are present, collect the clippings in a bagger and dispose of them in a shady place. Pulling. Most young weeds can be pulled from the soil. They will slide out most easily if you pull them when the soil is wet. Getting the root up is crucial, so think of the main stem as the root's handle, and grasp it as close to the soil line as you can. If you find that the weeds are breaking off at the crown as you pull, slip a kitchen fork, dandelion weeder, or similar tool under the weed, and pry and twist as you pull it up. Weeds that have taproots, such as dandelion and plantain, usually must be pried out. A flexible pair of waterproof gloves will keep your hands comfortable as you weed, and it's good to have a nice sitting pad, too. Let pulled weeds bake in the sun for a day or so before composting them. If pulled weeds are holding mature seeds, compost them separately in a hot, moist pile before using this compost in the garden.         منبع: مرکز مقالات کشاورزی AKE( بزرگترین وبلاگ کشاورزی ایران )           منبع: مرکز مقالات کشاورزی AKE( بزرگترین وبلاگ کشاورزی ایران )         Rosa multiflora   osa multiflora (Multiflora Rose, Baby Rose, Rambler Rose) is a species of rose native to eastern Asia, in China, Japan and Korea.   It is a scrambling shrub climbing other plants to a height of 3-5 m, with stout stems with recurved thorns (sometimes absent). The leaves are 5-10 cm long, compound, with 5-9 leaflets and feathered stipules. The flowers are produced in large corymbs, each flower small, 1.5-4 cm diameter, white or pink, borne in early summer. The hips are reddish to purple, 6-8 mm diameter.   Two varieties are accepted by the Flora of China:   * Rosa multiflora var. multiflora. Flowers white, 1.5-2 cm diameter. * Rosa multiflora var. cathayensis Rehder & E.H.Wilson. Flowers pink, to 4 cm diameter.       Rosa multiflora is grown as an ornamental plant, and also used as a rootstock for grafted ornamental rose cultivars.   In eastern North America, Multiflora Rose is now generally considered an invasive species, though it was originally planted as a soil conservation measure and to attract wildlife. It is readily distinguished from American native roses by its large inflorescences, which bear multiple flowers and hips, often more than a dozen, while the American species bear only one or a few on a branch.   Some places classify Multiflora rose as a "noxious weed" . In grazing areas, this rose is generally considered to be a serious pest, though it is considered excellent fodder for goats.           منبع: مرکز مقالات کشاورزی AKE( بزرگترین وبلاگ کشاورزی ایران )         Rosa gallica     Rosa gallica, (Gallic Rose, French Rose, or Rose of Provence) is a species of rose native to southern and central Europe eastwards to Turkey and the Caucasus. The rosa gallica officinalis is also called Apothecary's Rose.   It is a deciduous shrub forming large patches of shrubbery, the stems with prickles and glandular bristles. The leaves are pinnate, with three to seven bluish-green leaflets. The flowers are clustered one to four together, single with five petals, fragrant, deep pink. The hips are globose to ovoid, 10-13 mm diameter, orange to brownish.   Cultivation   The species is easily cultivated on well drained soil in full sun to semishade; it can survive temperatures down to −25 °C. It is one of the earliest cultivated species of roses, being cultivated by the Greek and Romans and it was commonly used in Mediaeval gardens. In the 19th century it was the most important species of rose to be cultivated, and most modern European rose cultivars have at least a small contribution from R. gallica in their ancestry.   Cultivars of the species R. gallica and hybrids close in appearance are best referred to a Cultivar Group as the Gallica Group roses. The ancestry is usually unknown and the influence of other species can not be ruled out.   The Gallica Group roses share the vegetative characters of the species, forming low suckering shrubs. The flowers can be single, but most commonly double or semidouble. The colours range from white (rare) to pink and deep purple. All Gallica Group roses are once flowering. They are easily cultivated.   The semidouble cultivar 'Officinalis', the "Red Rose of Lancaster", is the county flower of Lancashire.   In 2004, a cultivar of the Gallica Group named 'Cardinal de Richelieu' was genetically engineered to produce the first blue rose.           منبع: مرکز مقالات کشاورزی AKE( بزرگترین وبلاگ کشاورزی ایران )         Rosa canina   Rosa canina (lit. Dog Rose, often called incorrectly Rosehip) is a variable scrambling rose species native to Europe, northwest Africa and western Asia.   It is a deciduous shrub normally ranging in height from 1-5 m, though sometimes it can scramble higher into the crowns of taller trees. Its stems are covered with small, sharp, hooked spines, which aid it in climbing. The leaves are pinnate, with 5-7 leaflets. The flowers are usually pale pink, but can vary between a deep pink and white. They are 4-6 cm diameter with five petals, and mature into an oval 1.5-2 cm red-orange fruit, or hip.     Cultivation and uses   The plant is high in certain antioxidants. The fruit is noted for its high vitamin C level and is used to make syrup, tea and marmalade. It has been grown or encouraged in the wild for the production of vitamin C, from its fruit (often as rose-hip syrup), especially during conditions of scarcity or during wartime. The species has also been introduced to other temperate latitudes. During World War II in the United States Rosa canina was planted in victory gardens, and can still be found growing throughout the United States, including roadsides, and in wet, sandy areas up and down coastlines.   During the Vietnam War, for soldiers fighting with the North, Rosa canina was dried and then smoked with tobacco to produce mild hallucinogenic effects and abnormal dreams.[citation needed]   Forms of this plant are sometimes used as stocks for the grafting or budding of cultivated varieties.   The wild plant is planted as a nurse or cover crop, or stabilising plant in land reclamation and specialised landscaping schemes.   Numerous cultivars have been named, though few are common in cultivation. The cultivar Rosa canina 'Assisiensis' is the only dog rose without thorns.   The hips are used as a flavouring in the Slovenian soft drink Cockta.   The dog rose was the stylized rose of Medieval European heraldry, and is still used today.[citation needed]   The dog rose is the flower of Hampshire.   Etymology   The name 'dog' has a disparaging meaning in this context, indicating 'worthless' (by comparison with cultivated garden roses) (Vedel & Lange 1960).   Howard (1987) states that it was used in the eighteenth and nineteenth centuries to treat the bite of rabid dogs, hence the name "dog rose" arose.   Other old folk names include rose briar (also spelt brier), briar rose, dogberry, herb patience, sweet briar, wild briar, witches' briar, and briar hip.   In Turkish, its name is kuşburnu, which translates as "bird nose."   In Swedish, its name is nypon, which doesn't really translate.   In Azeri, its name is itburunu, which translates as "dog nose."             منبع: مرکز مقالات کشاورزی AKE( بزرگترین وبلاگ کشاورزی ایران )         Rosa dumalis   Rosa dumalis (Glaucous Dog Rose) is a species of rose native to Europe and southwest Asia. Not all authorities accept it as distinct, with the Flora Europaea treating it as a synonym of Rosa canina.   It is a shrub that grows 1-2 m high. It has long, bent thorns. It bears dark or light pink flowers in June and July. The hips are oval and quite soft. It may be confused with R. canina, but when flowering they are easy to tell apart since R. canina has white or light pink flowers. CASSIATORA Jun-12-------------------------------------------------------------------, 19:23 Rosa gigantea   Rosa gigantea is a species of rose native to northeast India, northern Myanmar and southwest China (Yunnan) in the foothills of the Himalaya at 1000-1500 m altitude. As its name suggests, it is the largest species of rose, climbing 20 m or more into the crowns of other trees by means of its stout, hooked thorns, and with a trunk up to 50 cm diameter. The leaves are semi-evergreen, 15-25 cm long, pinnate, with usually 7 leaflets, each leaflet 4-8 cm long. The flowers are white, creamy or yellow, the largest of any wild rose, 10-14 cm diameter. The hips are yellow or orange, 2.5-3.5 cm diameter, hard, and often lasting through the winter into the following spring, often still present at the same time as the next years' flowers. Another rose, described from Manipur in 1888 as R. macrocarpa and R. xanthocarpa by Sir George Watt, an authority on Indian roses, is now generally considered to be the same species as R. gigantea. The distinct characteristics claimed for R. macrocarpa (deeper yellow flowers, larger foliage with 4 to 7 leaflets and large yellow fruits) are not consistent.           منبع: مرکز مقالات کشاورزی AKE( بزرگترین وبلاگ کشاورزی ایران )         Rosa glauca       Rosa glauca (Red-leaved Rose or Redleaf Rose; syn. R. rubrifolia) is a species of rose native to the mountains of central and southern Europe, from Spanish Pyrenees east to Bulgaria and north to Germany and Poland.   It is a deciduous arching shrub of sparsely bristled and thorny cinnamon-coloured arching canes 1.5-3 m tall. The most distinctive feature is its leaves, which are glaucous blue-green to coppery or purplish, and covered with a waxy bloom; they are 5-10 cm long and have 5-9 leaflets. The fragile, clear pink flowers are 2.5-4 cm diameter, and are produced in clusters of two to five. The fruit is a dark red globose hip 10-15 mm diameter. Cultivation and uses   This rose was not widely grown in gardens until the end of the 19th century, when its refined wildness and beauty out of the flowering season first began to be appreciated. The flower petals fall off easily in the spray from watering hoses, as well as from wind and rain. The species is naturalised in northern Europe north of its native range, particularly in Scandinavia.   A hybrid with Rosa rugosa has been given the cultivar name 'Carmenetta'.           منبع: مرکز مقالات کشاورزی AKE( بزرگترین وبلاگ کشاورزی ایران )         Rosa laevigata     Rosa laevigata (Cherokee Rose) is a rose native to southern China and Taiwan south to Laos and Vietnam.   It is an evergreen climbing shrub, scrambling over other shrubs and small trees to heights of up to 5-10 m. The leaves are 3-10 cm long, with usually three leaflets, sometimes five leaflets, bright glossy green and glabrous. The flowers are 6-10 cm diameter, fragrant, with pure white petals and yellow stamens, and are followed by bright red and bristly hips 2-4 cm diameter. The flower stem is also very bristly.   Cultivation and symbolism   The species was introduced to the southeastern United States in about 1780, where it soon became naturalized, and where it gained its English name. It is the state flower of Georgia. The flower is forever linked to the Trail of Tears and its petals represent the women's tears shed during the period of great hardship and grief throughout the historical trek from the Cherokees' home to U.S. Forts such as Gilmer among others. The flower has a gold center, symbolizing the gold taken from the Cherokee tribe.           منبع: مرکز مقالات کشاورزی AKE( بزرگترین وبلاگ کشاورزی ایران )         Rosa rubiginosa     osa rubiginosa (Sweet briar or Eglantine Rose; syn. R. eglanteria) is a species of rose native to Europe and western Asia, from France and the British Isles north to southern Scandinavia and east to western Russia and Turkey.   It is a dense deciduous shrub 2-3 m high and across, with the stems bearing numerous hooked prickles. The foliage has a strong apple-like fragrance. The leaves are pinnate, 5-9 cm long, with 5-9 rounded to oval leaflets with a serrated margin, and numerous glandular hairs. The flowers are 1.8-3 cm diameter, the five petals being pink with a white base, and the numerous stamens yellow; the flowers are produced in clusters of 2-7 together, from late spring to mid summer. The fruit is a globose to oblong red hip 1-2 cm diameter.   Etymology   The name 'eglantine' derives from Latin aculeatus (thorny), by way of old French aiglant. 'Sweet' refers to the apple fragrance of the foliage, while 'briar' (also sometimes 'brier') is an old Anglo-Saxon word for any thorny shrub (Vedel & Lange 1960).   Cultivation and uses   In addition to its pink flowers, it is valued for its scent, and the hips that form after the flowers and persist well into the winter. Graham Thomas recommends that it should be planted on the south or west side of the garden so that the fragrance will be brought into the garden on warm, moist winds.   In New Zealand it is an invasive species, classed as a Regional Plant Pest. In southeast Australia it is also invasive.   It is also listed as a Category 1 Declared Weed in South Africa. These plants may no longer be planted or propagated, and all trade in their seeds, cuttings or other propagative material is prohibited.v           منبع: مرکز مقالات کشاورزی AKE( بزرگترین وبلاگ کشاورزی ایران )         Rosa rugosa     Rosa rugosa (Rugosa Rose, Japanese Rose, or Ramanas Rose) is a species of rose native to eastern Asia, in northeastern China, Japan, Korea and southeastern Siberia, where it grows on the coast, often on sand dunes. The Japanese name is (ハマナス(hamanasu)), meaning "shore pear".     It is a suckering shrub which develops new plants from the roots and forms dense thickets 1–1.50 m tall with stems densely covered in numerous short, straight thorns 3-10 mm long. The leaves are 8–15 cm long, pinnate with 5–9 leaflets, most often 7, each leaflet 3–4 cm long, with a distinctly corrugated (rugose, hence the species' name) surface. The flowers are pleasantly scented, dark pink to white, 6–9 cm across, with somewhat wrinkled petals; flowering is from summer to autumn (June to September in the northern hemisphere).   The hips are large, 2–3 cm diameter, and often shorter than their diameter, not elongated like most other rose hips; in late summer and early autumn the plants often bear fruit and flowers at the same time. The leaves typically turn bright yellow before falling in autumn.   Cultivation and uses   Rugosa Rose is widely used as an ornamental plant. It has been introduced to numerous areas of Europe and North America. It has many common names, several of which refer to the fruit's resemblance to a tomato, including beach tomato or sea tomato; saltspray rose and beach rose are others.   The sweetly scented flowers are used to make pot-pourri in Japan and China, where it has been cultivated for about a thousand years.   This species hybridises readily with many other roses, and is valued by rose breeders for its considerable resistance to the diseases rose rust and rose black spot. It is also extremely tolerant of seaside salt spray and storms, commonly being the first shrub in from the coast. It is widely used in landscaping, being relatively tough and trouble-free. Needing little maintenance, it is suitable for planting in large numbers; its salt-tolerance makes it useful for planting beside roads which need deicing with salt regularly.   Numerous cultivars have been selected for garden use, with flower colour varying from white to dark red-purple, and with semi-double to double flowers where some or all of the stamens are replaced by extra petals. Popular examples include 'Fru Dagmar Hastrup' (pink, single), 'Pink Grootendorst' (pink, semi-double), and 'Blanc Double du Coubert' (white, double)..           منبع: مرکز مقالات کشاورزی AKE( بزرگترین وبلاگ کشاورزی ایران )         Rosa virginiana     Rosa virginiana, commonly known as the Virginia Rose , Common Wild Rose or Prairie Rose, is a woody perennial in the rose family native to eastern North America. In the Canadian maritimes, it grows with at an almost invasive rhythm. It is seen in meadows, vacant lots, ditches, even in dumps.           منبع: مرکز مقالات کشاورزی AKE( بزرگترین وبلاگ کشاورزی ایران )         Flower     ()       A flower, also known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Magnoliophyta, also called angiosperms). The biological function of a flower is to mediate the union of male sperm with female ovum in order to produce seeds. The process begins with pollination, is followed by fertilization, leading to the formation and dispersal of the seeds. For the higher plants, seeds are the next generation, and serve as the primary means by which individuals of a species are dispersed across the landscape. The grouping of flowers on a plant are called the inflorescence.   In addition to serving as the reproductive organs of flowering plants, flowers have long been admired and used by humans, mainly to beautify their environment but also as a source of food.   Flower specialization and pollination   Each flower has a specific design which best encourages the transfer of its pollen. Cleistogamous flowers are self pollinated, after which, they may or may not open. Many Viola and some Salvia species are known to have these types of flowers.   Entomophilous flowers attract and use insects, bats, birds or other animals to transfer pollen from one flower to the next. Flowers commonly have glands called nectaries on their various parts that attract these animals. Some flowers have patterns, called nectar guides, that show pollinators where to look for nectar. Flowers also attract pollinators by scent and color. Still other flowers use mimicry to attract pollinators. Some species of orchids, for example, produce flowers resembling female bees in color, shape, and scent. Flowers are also specialized in shape and have an arrangement of the stamens that ensures that pollen grains are transferred to the bodies of the pollinator when it lands in search of its attractant (such as nectar, pollen, or a mate). In pursuing this attractant from many flowers of the same species, the pollinator transfers pollen to the stigmas—arranged with equally pointed precision—of all of the flowers it visits.   Anemophilous flowers use the wind to move pollen from one flower to the next, examples include the grasses, Birch trees, Ragweed and Maples. They have no need to attract pollinators and therefore tend not to be "showy" flowers. Male and female reproductive organs are generally found in separate flowers, the male flowers having a number of long filaments terminating in exposed stamens, and the female flowers having long, feather-like stigmas. Whereas the pollen of entomophilous flowers tends to be large-grained, sticky, and rich in protein (another "reward" for pollinators), anemophilous flower pollen is usually small-grained, very light, and of little nutritional value to insects.   Morphology   Flowering plants are heterosporangiate, producing two types of reproductive spores. The pollen (male spores) and ovules (female spores) are produced in different organs, but the typical flower is a bisporangiate strobilus in that it contains both organs.   A flower is regarded as a modified stem with shortened internodes and bearing, at its nodes, structures that may be highly modified leaves.[1] In essence, a flower structure forms on a modified shoot or axis with an apical meristem that does not grow continuously (growth is determinate). Flowers may be attached to the plant in a few ways. If the flower has no stem but forms in the axil of a leaf, it is called sessile. When one flower is produced, the stem holding the flower is called a peduncle. If the peduncle ends with groups of flowers, each stem that holds a flower is called a pedicel. The flowering stem forms a terminal end which is called the torus or receptacle. The parts of a flower are arranged in whorls on the torus. The four main parts or whorls (starting from the base of the flower or lowest node and working upwards) are as follows:   * Calyx: the outer whorl of sepals; typically these are green, but are petal-like in some species. * Corolla: the whorl of petals, which are usually thin, soft and colored to attract insects that help the process of pollination. * Androecium (from Greek andros oikia: man's house): one or two whorls of stamens, each a filament topped by an anther where pollen is produced. Pollen contains the male gametes. * Gynoecium (from Greek gynai****************** oikia: woman's house): one or more pistils. The female reproductive organ is the carpel: this contains an ovary with ovules (which contain female gametes). A pistil may consist of a number of carpels merged together, in which case there is only one pistil to each flower, or of a single individual carpel (the flower is then called apocarpous). The sticky tip of the pistil, the stigma, is the receptor of pollen. The supportive stalk, the style becomes the pathway for pollen tubes to grow from pollen grains adhering to the stigma, to the ovules, carrying the reproductive material.   Although the floral structure described above is considered the "typical" structural plan, plant species show a wide variety of modifications from this plan. These modifications have significance in the evolution of flowering plants and are used extensively by botanists to establish relationships among plant species. For example, the two subclasses of flowering plants may be distinguished by the number of floral organs in each whorl: dicotyledons typically having 4 or 5 organs (or a multiple of 4 or 5) in each whorl and monocotyledons having three or some multiple of three. The number of carpels in a compound pistil may be only two, or otherwise not related to the above generalization for monocots and dicots.   In the majority of species individual flowers have both pistils and stamens as described above. These flowers are described by botanists as being perfect, bisexual, or hermaphrodite. However, in some species of plants the flowers are imperfect or unisexual: having only either male (stamens) or female (pistil) parts. In the latter case, if an individual plant is either female or male the species is regarded as dioecious. However, where unisexual male and female flowers appear on the same plant, the species is considered monoecious.   Additional discussions on floral modifications from the basic plan are presented in the articles on each of the basic parts of the flower. In those species that have more than one flower on an axis—so-called composite flowers—the collection of flowers is termed an inflorescence; this term can also refer to the specific arrangements of flowers on a stem. In this regard, care must be exercised in considering what a ‘‘flower’’ is. In botanical terminology, a single daisy or sunflower for example, is not a flower but a flower head—an inflorescence composed of numerous tiny flowers (sometimes called florets). Each of these flowers may be anatomically as described above. Many flowers have a symmetry, if the perianth is bisected through the central axis from any point, symmetrical halves are produced—the flower is called regular or actinomorphic, e.g. rose or trillium. When flowers are bisected and produce only one line that produces symmetrical halves the flower is said to be irregular or zygomorphic. e.g. snapdragon or most orchids.   Floral formula   A floral formula is a way to represent the structure of a flower using specific letters, numbers, and symbols. Typically, a general formula will be used to represent the flower structure of a plant family rather than a particular species. The following representations are used:   Ca = calyx (sepal whorl; e.g. Ca5 = 5 sepals) Co = corolla (petal whorl; e.g., Co3(x) = petals some multiple of three ) Z = add if zygomorphic (e.g., CoZ6 = zygomorphic with 6 petals) A = androecium (whorl of stamens; e.g., A∞ = many stamens) G = gynoecium (carpel or carpels; e.g., G1 = monocarpous)   x: to represent a "variable number" ∞: to represent "many"   A floral formula would appear something like this:   Ca5Co5A10 - ∞G1           منبع: مرکز مقالات کشاورزی AKE( بزرگترین وبلاگ کشاورزی ایران )