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Monocotyledons, also known as monocots, are one of two major groups of flowering plants (or angiosperms) that are traditionally recognized, the other being dicotyledons, or dicots. Monocot seedlings typically have one cotyledon (seed-leaf), in contrast to the two cotyledons typical of dicots. Monocots have been recognized at various taxonomic ranks, and under various names (see below). The APG II system recognises a clade called "monocots" but does not assign it to a taxonomic rank.
According to the IUCN there are 59,300 species of monocots. The largest family in this group (and in the flowering plants as a whole) by number of species are the orchids (family Orchidaceae), with more than 20,000 species. In agriculture the majority of the biomass produced comes from monocots. The true grasses, family Poaceae (Gramineae), are the most economically important family in this group. These include all the true grains (rice, wheat, maize, etc.), the pasture grasses, sugar cane, and the bamboos. True grasses have evolved to become highly specialised for wind pollination. Grasses produce much smaller flowers, which are gathered in highly visible plumes (inflorescences). Other economically important monocot families are the palm family (Arecaceae), banana family (Musaceae), ginger family (Zingiberaceae) and the onion family Alliaceae, which includes such ubiquitously used vegetables as onions and garlic.
The name monocotyledons is derived from the traditional botanical name Monocotyledones, which derives from the fact that most members of this group have one cotyledon, or embryonic leaf, in their seeds. By contrast, the traditional dicotyledons typically have two cotyledons. From a diagnostic point of view the number of cotyledons is neither a particularly handy (as they are only present for a very short period in a plant's life), nor totally reliable character.
Nevertheless, monocots are a distinctive group. One of the most noticeable traits is that a monocot's flower is trimerous, with the flower parts in threes or in multiples of three. That is to say, a monocotyledon's flower typically has three, six, or nine petals. Many monocots also have leaves with parallel veins.
Monocots evolved from a single ancestor, and are younger than dicots, from which they probably branched off, as recent genetic research has shown. They evolved 100-120 million years ago, shortly after the flowering plant explosion.
Morphology, compared to the (broadly defined) dicotyledons
The traditionally listed differences between monocotyledons and dicotyledons are as follows. This is a broad sketch only, not invariably applicable, as there are a number of exceptions. The differences indicated are more true for monocots versus eudicots.
A number of these differences are not unique to the monocots. For example, trimerous flowers and monosulcate pollen are also found in magnoliids. Exclusively adventitious roots are found also in Nymphaeaceae and some of the Piperaceae. Similarly, at least one of these traits, parallel leaf veins, is far from universal among the monocots. Monocots with reticulate leaf veins are found in a wide variety of monocot families: for example, Trillium,Smilax(greenbriar), andPogonia(an orchid), and theDioscoreales. Nevertheless, this list of traits is a generally valid set of contrasts, especially when contrasting monocots with eudicots rather than non-monocot flowering plants in general.
Some monocots, such as grasses, have hypogeal emergence, where the mesocotyl elongates and pushes the coleoptile (which encloses and protects the shoot tip) toward the soil surface. Since elongation occurs above the cotyledon, it is left in place in the soil where it was planted. Many dicots have epigeal emergence, in which the hypocotyl elongates and becomes arched in the soil. As the hypocotyl continues to elongate, it pulls the cotyledons upward, above the soil surface.
Monocots have a distinctive arrangement of vascular tissue known as an atactostele in which the vascular tissue is scattered rather than arranged in concentric rings. Many monocots are herbaceous and do not have the ability to increase the width of a stem (secondary growth) via the same kind of
Monocots, or monocotyledons, are a class of the flowering plants, or angiosperms. Monocots are named for and recognized by the single cotyledon , or seed leaf, within the seed. The first green blade emerging from the seed upon germination is the cotyledon, which contains sugars and other nutrients for growth until the leaf is able to photosynthesize. Monocots comprise about 67,000 species, or one-quarter of all flowering plants. They include not only the very large grass family (Poaceae, 9,000 species), but also the orchid family (Orchidaceae, 20,000 species), and the sedge family (Cyperaceae, 5,000 species), as well as palms, lilies, bromeliads (including pineapple), and the Araceae, which includes skunk cabbage and philodendron. The angiosperms have traditionally been divided into monocots and dicots alone, but recent work has shown that while monocots form a natural evolutionary group, dicots do not, and so the angiosperms are now grouped into monocots, eudicots , and basal angiosperms. In addition to the single cotyledon in the seed, monocots can be recognized by the arrangement of vascular tissue in the stem. Vascular tissue includes xylem , used for water transport from the roots, and phloem , which carries sugars and other nutrients from the leaves to other tissues throughout the plant. Unlike other angiosperms, whose vascular tissue is arranged in rings around the periphery, the vascular bundles of monocots are scattered throughout the stem. One consequence of this is that monocots cannot form annual rings of hardened tissueâ€”woodâ€”and so are limited in the strength of their stems. Nonetheless, some monocots, notably the palms, do attain significant height. Leaves of monocots have parallel veins, as seen in grass. The roots of monocots also differ from other flowering plants. In monocots, the first root to emerge from the seed dies off, and so no strong, central tap root forms. Instead, monocots sprout roots from shoot tissue near the base, called adventitious roots. The familiar fibrous root system of grasses is an example of this rooting pattern. Many monocots form bulbs, such as onion, gladiolus, and tulips. These are not root structures, but rather modified stems, made of compact leaves. This can be easily seen in the layers of the onion. Most monocot flowers have flower parts in sets of three, so that there may be three or six petals, for instance, along with three egg-bearing carpels and pollen-bearing stamens in some multiple of three. The pollen grains of monocots have a single slit, or aperture, which splits open to allow the pollen tube to grow during fertilization . In contrast, the pollen grain of eudicots has three apertures. Orchid flowers are among the most beautiful and complex of all flowers, due in part to their long and specialized relationship with specific pollinators. Some orchid flowers have evolved to resemble the female of the bee species that pollinates them, luring the male in to attempt copulation. During this process, the pollen, all of which is retained in a single, sticky mass, is transferred to the male bee, who will carry it to the next flower in another fruitless attempt to find a mate. In contrast to the showy orchids, grass flowers are rather simple and dull, in keeping with the absence of any need to attract insects. Grass flowers are suspended at the tip of the plant, where wind can carry the pollen away to land on the female flower of a neighboring plant. Three grassesâ€”corn, wheat, and riceâ€”provide the vast majority of calories consumed by humans throughout the world. Their seeds, called grain, are rich in carbohydrates and contain some protein and vitamins as well. see also Angiosperms; Eudicots; Evolution of Plants; Flowers; Grain; Grasses; Leaves; Roots; Seeds; Shoots Richard Robinson Raven, Peter H., Ray F. Evert, and Susan E. Eichhorn. Biology of Plants, 6th ed. New York: W. H. Freeman and Company, 1999.
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Answers:1. The first angiosperms had pollen with a single furrow or pore through the outer layer (monosulcate). This feature is retained in the monocots, but most dicots are descended from a plant which developed three furrows or pores in its pollen (triporate). 2. After male meiosis, each pollen mother cell splits into a rounded tetrad of four haploid nuclei before cell wall formation
Answers:DICOTS Dicot plants differ in structures of their seeds, foliage and flowers, from the monocotyledons. They can be easily distinguished by studying their distinct characteristics. Let us learn about each feature of the dicot plants in detail. Seed The most important difference between the monocots and dicots is the number of embryonic leaves, or cotyledons. There are two cotyledons in the seeds of dicot plants that actually emerge above the soil, when the seed germinates. They then turn green and form the first two leaves of the new plant. Leaves The leaves of the dicot plants have veins that form a branched pattern, unlike monocots, in which they run parallel. The veins are actually netted or webbed on the whole surface of the leaf, in dicot plants. Vascular Structure The stems of dicot plants have vascular bundles, consisting of two structures, the xylem and the phloem. The xylem helps to transport water and minerals from the root to the other parts of the plant and the phloem transports food that is made in the leaves, to the storage organs. These vascular bundles are arranged in a circular manner around the edge of the stem. Flowers The flower parts of dicot plants are usually present in fours or fives. Sometimes, they are found in multiples of either numbers. These flower parts include petals, sepals and pistils, or the reproductive parts of the plant. Roots Roots of dicot plants are often fibrous and branched. They branch out in many smaller parts that form a dense network of root system, unlike monocot plants, that have a tap root system. SEE HERE http://library.thinkquest.org/3715/seeds.html http://www.ucmp.berkeley.edu/glossary/gloss8/monocotdicot.html http://www.howtoorganicgarden.com/new_page_2.htm
Answers:There's a very easy way to tell whether a plant is dicot or monocot. Look at the veins in the leaf. If they branch out like a tree (dendritic pattern) they are dicots. If the veins are parallel, like the veins in a blade of grass or a corn leaf, it's a monocot. The first link is a pic of an oak leaf, which is a dicot. The second link is a pic of the parallel veins of a corn leaf. Also, dicot flowers tend to have flower parts in multiples of four or five (petals, stamens, sepals). Monocot flowers tend to have flower parts in multiples of threes.
Answers:Grass is the classic example of a monocotyledon plant. The first shoot sent up on germination is a single leaf. A pea is a good example of a dicotyledon. Cotyledon is the first leaf that appears on germination. 'Mono' means one, 'di' means two. The traditional differences between monocots and dicots are: Flowers: In monocots, flowers are trimerous (number of flower parts in a whorl in threes) while in dicots the flowers are tetramerous or pentamerous (flower parts are in fours or fives). Pollen: In monocots, pollen has one furrow or pore while dicots have three. Seeds: In monocots, the embryo has one cotyledon while the embryo of the dicot has two. Stems: In monocots, vascular bundles in the stem are scattered, in dicots arranged in a ring. Roots: In monocots, roots are adventitious, while in dicots they develop from the radicle. slice of onion, showing parallel veins in cross section slice of onion, showing parallel veins in cross section Leaves: In monocots, the major leaf veins are parallel, while in dicots they are reticulate. Not all of these, though, are necessarily definitive. The leaves of most pine trees (which are multicotyledinous) have parallel veins, for example. There is a good picture of a monocot and a dicot seedling side by side here: http://en.wikipedia.org/wiki/Cotyledon