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From Wikipedia

Monocotyledon

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.

Many plants cultivated for their blooms are also from the monocot group, notably lilies, daffodils, irises, amaryllis, orchids, cannas, bluebells and tulips.

Name, characters

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.

Evolution

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.

Emergence

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.

Vascular system

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

Cotyledon

A cotyledon (ˌkoʊtɛlɪdɔ�n; "seed leaf" from Greek: κοτυληδών kotylēd�n, gen.: κοτυληδόνος kotylēdonos, from κοτ�λη kotýlē "cup, bowl"), is a significant part of the embryo within the seed of a plant. Upon germination, the cotyledon may become the embryonic first leaves of a seedling. The number of cotyledons present is one characteristic used by botanists to classify the flowering plants (angiosperms). Species with one cotyledon are called monocotyledonous (or, "monocots") and placed in the class Liliopsida. Plants with two embryonic leaves are termed dicotyledonous ("dicots") and placed in the class Magnoliopsida.

In the case of dicot seedlings whose cotyledons are photosynthetic, the cotyledons are functionally similar to leaves. However, true leaves and cotyledons are developmentally distinct. Cotyledons are formed during embryogenesis, along with the root and shoot meristems, and are therefore present in the seed prior to germination. True leaves, however, are formed post-embryonically (i.e. after germination) from the shoot apical meristem, which is responsible for generating subsequent aerial portions of the plant.

The cotyledon of grasses and many other monocotyledons is a highly modified leaf composed of a scutellumand acoleoptile. The scutellum is a tissue within the seed that is specialized to absorb stored food from the adjacentendosperm. The coleoptile is a protective cap that covers the plumule (precursor to the stem and leaves of the plant).

Gymnosperm seedlings also have cotyledons, and these are often variable in number (multicotyledonous), with from 2 to 24 cotyledons forming a whorl at the top of the hypocotyl (the embryonic stem) surrounding the plumule. Within each species, there is often still some variation in cotyledon numbers, e.g. Monterey Pine (Pinus radiata) seedlings have 5–9, and Jeffrey Pine (Pinus jeffreyi) 7–13 (Mirov 1967), but other species are more fixed, with e.g. Mediterranean Cypress always having just two cotyledons. The highest number reported is for Big-cone Pinyon (Pinus maximartinezii), with 24 (Farjon & Styles 1997).
The cotyledons may be ephemeral, lasting only days after emergence, or persistent, enduring a year or more on the plant. The cotyledons contain (or in the case of gymnosperms and monocotyledons, have access to) the stored food reserves of the seed. As these reserves are used up, the cotyledons may turn green and begin photosynthesis, or may wither as the first true leaves take over food production for the seedling.

Epigeal versus hypogeal development

Cotyledons may be either epigeal, expanding on the germination of the seed, throwing off the seed shell, rising above the ground, and perhaps becoming photosynthetic; or hypogeal, not expanding, remaining below ground and not becoming photosynthetic. The latter is typically the case where the cotyledons act as a storage organ, as in many nuts and acorns.

Hypogeal plants have (on average) significantly larger seeds than epigeal ones. They also are capable of surviving if the seedling is clipped off, as meristem buds remain underground (with epigeal plants, the meristem is clipped off if the seedling is grazed). The tradeoff is whether the plant should produce a large number of small seeds, or a smaller number of seeds which are more likely to survive.

Related plants show a mixture of hypogeal and epigeal development, even within the same plant family. Groups which contain both hypogeal and epigeal species include, for example, the Araucariaceae family of Southern Hemisphere conifers, the Fabaceae (pea family), and the genus Lilium(seeLily seed germination types).

History

The term cotyledon was coined by Marcello Malpighi. John Ray was the first botanist to recognise that some plants have two and others only one, and eventually the first to recognise the immense importance of this fact to systematics.



From Encyclopedia

Monocots Monocots

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 tissue—wood—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 grasses—corn, wheat, and rice—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.


From Yahoo Answers

Question:

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

Question:Identify each by their leaf venation, flower arrangement, root system, number of cotyledons, arrangement of leaves in stem Example: Name of plant: Apple Tree Leaf venation: Netted flower arrangement: multiples of 4 or 5 Root system: tap root arrangement of leaves in stem: whorled(this is a question too, what is the true leaf arrangement of apple tree:whorled, alternate or opposite....? For identifying, choose here Leaf venation: Netted or parallel Flower arrangement: Multiples of 4 or 5, multiples of 3 root system: taproot or fibrous number of cotyledons: one (monocot) or two (dicot) Arrangement of leaves in stem: Alternate, Opposite, Whorled Complete Identification and 10 examples will be the best answer

Answers:Monocotyledonous Plant Orders & Their Families http://www.floresflowers.com/taxa/Monocots.html http://www.pierce.ctc.edu/biology/EMbuja/BIOL203/Monocots.htm Dicot plant families & their genera http://www.floresflowers.com/taxa/Dicots.html Pick you plants and look them up on Zip Code Zoo. For example the palm tree family Arecaceae are monocots. Cocos nucifera (Coconut Palm) http://zipcodezoo.com/Plants/C/Cocos_nucifera/

Question:I'm having a hard time understanding the difference between a dicot plant and a monocot plant. Is this flower an example of a dicot plant with flower & leaf or a monocot plant with flower & leaf? Thanks in advance! http://i93.photobucket.com/albums/l45/briannanicole768/PictureorVideo1227.jpg

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.

Question:I need to do a drawing of a monocot with two modifications...either one stem and one leaf, or one leaf and one root etc. I need to do the same with a dicot. But so far I can't find a plant with more than one modification. Does anyone know any??

Answers:Pumpkins are dicot, their leaves are prickly as a 'defense mechanism' to ward of any creature that might want to eat the fruit. They tend to grow and extend, the roots grow into whatever surface it can and has vines that coil around surrounding environment. ( i know this because we have pumpkins growing in the backyard and the roots are wrapped around our porch swing) You could draw a close up of a pumpkin leaf, and the way the roots grow. Here are some other fun facts that might help: Bulbs In some monocots, leaf bases grow to form bulbs, underground organs used for food storage. They can be identified from the series of leaf bases fitting inside each other, with a central shoot apical meristem. Stem Tubers In some dicotyledon plants, stems grow downwards into the soil and sections of them grow into stem tubers, also used for food storage. They are identified as their vascular bundles are arranged in rings reminiscent of stem bundles. Storage Roots These roots are swollen with stores of food, identified by the central location of vascular tissue. Tendrils These narrow outgrowths from leaves rotate through the air until they touch a solid support to which they attach, allowing the plant to climb upward