Magnoliophyta

History

It is undoubtedly Théophraste (v. 372 av. J. - C. - 287 av. J. - C.) which, the first, distinguishes Angiospermes from the Gymnosperme S. John Ray uses, at the end of the 17th century, this difference in its classification which is the first attempt at natural classification of the modern time.

Reproduction of the angiospermes

Asexual reproduction

Angiospermes present the reproductive system most advanced of the plants. In fact besides the reproductive bodies (flowers and fruits) are the most visible characteristics of the group.

Angiospermes lay out of a very great number of possibilities of asexual Reproduction (mode of reproduction uniparental but not necessarily clonal). One already quoted various the Parthénogenèse S, but exist also more known processes related to the fragmentation of the thallus (certain graminaceous not selected by the Man needing to be moderately trampled for better spreading by asexual reproduction clonale in the medium). These processes are related to the Totipotence nonapoptotic vegetable cells (i.e. it quasi totality of the vegetable cells, those constituting the various circulatory systems being apoptotic or sowing-apoptotiques). One will be able to quote the exploitation of this potentiality by the Man, in particular the techniques of Bouturage, Marcottage forced or simply the fragmentation of the rhizomes or the tubers. Angiospermes use extensions racinaires or caulinaires as stolons them and the suckers, in particular at Populus , a poplar which can result only from one sucker, a whole wood can actually be one individual. It is also the case at the bamboo which, to compensate for its great slowness to generate flowers (sometimes several tens of years before reaching sexual maturity) reproduces in a superabundant way by emission of rhizomes.

Finally one will be able to also quote the asexual reproduction clonale by apoflorie: formation of buds mitotic called bulblets, which become small individuals developing their cormus (stem and root) on the plant itself before being detached about it. One observes this mode of reproduction at Kalanchoe pinnata in particular (plant crowned of Aztec).

The essential asset of the evolutionary success of Angiospermes with respect to Gymnospermes will have been the massive recourse to the asexual reproduction which makes it possible to multiply the phenotypes adapted to their environment without the individuals necessarily not reaching sexual maturity.

Sexuée reproduction

The organization of the floral parts

The terms Fleur and Plante are often confused by nonthe botanists. However, it must be noted that the flowers constitute only the reproductive part of certain plants - the plants with flower. The flower consists of several parts, of which the cheesecloth S (constituting the male part), and the Pistil (constituting the female part). A flower hermaphrodite is a flower having at the same time cheesecloths and pistil.

The distribution of the sexes at the plants with flowers

Angiospermes are with reproduction mainly sexuée, with some cases of Parthénogenèse (dandelions).

The majority (70%) are hermaphrodite S (the individuals have the two sexes), with in general of the mixed flowers. However, at other species, the male and female flowers are separate on the same individual (species Monoïque S, such as the hazel tree and corn). Other combinations are possible (male flowers hermaphrodites and flowers on the same foot for example).

Some species (approximately 7%) are with sexes separated on separate plant (the individuals are male or female, for example the houx, kiwi, one speaks about species Dioïque), even flower hermaphrodite and male flower on different feet (gynodioïque Espèce). Lastly, one notes more curious reproductive cycles, like the case of the Figuier.

The individuals are not necessarily car-fertilizable S (in other words fecundation is not always possible on the same plant).

Life cycle of Angiospermes

Like all the plants, Angiospermes present an alternation between two states: the state sporophytic and the state gametophytic. However this alternation belongs to a very unbalanced cycle: the gametophytic phase is very reduced in space and time, which corresponds to a better adaptation in the middle of nonwatery life of Angiospermes. Indeed the exposure to the sun increasing the risks of changes, a predominance of the sporophytic phase (on the greatest level of ploïdie) avoids expressing the recessive changes directly. Moreover the sporophyte (for example a tree) is invariably more resistant at the plants.

The gamétophytes male and female correspond respectively to the grain of pollen and the embryonic bag at Angiospermes. One would be thus wrong to think that the grain of pollen or that the embryonic bag (itself contained in the ovule , from where confusion) are gamètes: they is indeed completely false since they contain the gamètes or the futures gamètes.

The grain of pollen

The embryonic Bag

It can be monosporé or tétrasporé, i.e. to come from only one mégaspore of the sporophyte or tetrad of spores resulting from the same meiosis. It is a fabric ( not a gamète ) gametophytic ( container the gamète female). It can present 7 or 4 cells. In the case of an embryonic bag with seven cells, are present there:

the oosphere, i.e. the fertilizable cell or the gamète female.
two synergides, auxiliary cells of fecundation which form a Tore around the oosphere and which will assume the role of hopper to make forward the male gamète. These cells can possibly generate an embryo nonzygotic in certain cases of asexual reproduction.
Three antipodes located at the other end of the embryonic bag.
a central cell with two cores (known as polar) which will amalgamate with the male second gamète at the time of the double fertilization for possibly to give endosperm.

The embryonic bag thus contains and protects the gamète female of which it will support fecundation. It itself is locked up in the nucellus inside the bitégumenté ovule.

Pollination

Fecundation

The seed

Fruit

The dispersion of the offspring

The fruit unit and seed are called diaspore, the fruit is a structure only ovarienne (this is why one speaks in many cases about “false fruits”, apple and the strawberry by forming part) while the seed comes from the ovule.

The seed and the fruit correspond to a certain form of Viviparité. The embryo of Angiospermes develops initially protected and supplied with his/her relative female, then is released, in a state of slowed down life (Diapause), provided with food protections and reserves (fruit). Certain fruits present in addition to the characteristics allowing dispersion at important distances. One can quote the brushes of the dandelions, which make that the wind transports seeds on tens of meters. Let us quote also the setting with contribution of mammals for transport (by fixing in the hairs or, less important it should be admitted in the socks of campers). Another mode of dispersion is observed when animals consume certain fruits: they can then release nonedible seed and its envelopes far from his/her relative (before or after intestinal transit time, according to). It is in addition clear that an imitation and a coévolution can be in question in the adaptation of the plants to flowers to fauna able to disperse their offspring. One knows for example certain seeds whose dormancy is specifically raised by digestive enzymes of specific animals (for example some Acacia S African).

Also: Pericarp, Akène, Drupe, Fruit parthenocarpic, fleshy Fruit, dry Fruit indéhiscent

Specificity of the natural conditions

Being fixed and in nonaqueous medium, Angiospermes have to face a very great number of selective pressures. it is in particular for this reason which they are much diversified than Thallophytes (algae) which, they, develop within a medium very little changing. In fact Angiospermes represent the subphylum more diversified of Chlorobiontes (green line). This diversification necessarily passes by a genotypic diversity. Thus the descent of a angiosperme in wild conditions always tends not to be homogeneous, and thus to present a very broad range of different genotypes.

To maintain this genetic diversity, the plants have recourse to the cross-fertilization (mode of reproduction sexuée at the species whose individuals interfécondent themselves systematically, in opposition to self-fertilization who was selected by the Man, we will see for which reasons) which makes impossible to circumvent the broad diffusion of pollen. Only one descent thus counts a very great number of different genotypes which will lead to phenotypes of which some certainly will be very well adapted to the medium (the others will die). The most adapted having the asexual reproduction then to multiply before to have reached sexual maturity. One knows various modes supporting the cross-fertilization (being opposed to self-fertilization).

Systems of (car) Incompatibility Sporophytiques and Gamétophytiques (LOCATED and SIG). They are reactions of rejection of the autopollen (pollen coming from the oneself ). It was seen, the grain of pollen is composed of two to three cells and is surrounded of the sporoderme primarily composed of the most resistant material at the Alive one: the sporopollenine . this sporoderme is composed of two layers: intine and the exine from which the origins are very different. The exine (which presents the apertures) was synthesized by the sporophyte, and thus presents certain molecules (RNAses and glycoprotéines) which result from the expression of alleles sporophytic. These proteins are recognized when the autopollen arrives at the level of the mark, and they start the autoincompatibility Sporophytique (by recognition of molecules synthesized by the sporophyte). This rejection meets in the case of pollen tricellulaire.
L' autoincompatibility Gamétophytique rests on the same principle, but is based on the recognition of substances synthesized by the male gamétophyte (i.e. the grain of pollen at Angiospermes). These substances are contained in the intine and are recognized at the time of the germination of the pollen which is then rejected. The LOCATED one meets at species with pollen bicellulaire.

shifts of maturity. At certain species the male parts of the flower are mature before the female parts (protandrie) or after (protogynie, rarer), which reduces the number of autofécondations considerably.

floral dimorphism: the species having developed this system present two types of individuals in equal proportions in their population. Individuals with longistylées flowers (long style, mark with the top of cheesecloths, small grains of pollen and large stigmatic papillae) and individuals with brévistylées flowers (short style, cheesecloths with the top of the mark but coarse grains of pollen and small stigmatic papillae). This dimorphism prevents the autofecondation because in both cases the autopollen cannot penetrate the mark of the style, either because it is too large, or because the style is too high.

Anatomy and growth

Angiospermes are in majority Phototrophe S, drawing to them energy from solar light and them Carbone of atmospheric carbon dioxide. Some species are partially parasitic (GUI), others are completely, or are to it Saprophyte S and, in these the last two cases, are deprived of Chlorophylle. Let us quote the case of Mycotrophe S, Angiospermes without chlorophyl living in symbiotic relation with mushrooms (certain orchises, and the Monotrope S).

Angiospermes, like other Spermatophytes, develop a important system racinaire enabling them to draw from the ground the Eau and the Rock salt which they need. The root S are often the seat of Symbiose S with the Bactérie S of the ground, in particular for the metabolism of the Azote. Certain species, alive frequently on very poor grounds, supplement their contribution nitrogenizes some by the capture of animals (plants carnivores).

Also: Méristème, Liber, Phloem, Xylème, root, Mode of ramification of the plants with flower, Sheet

Phylogeny and classification

See also: Contenu=Voir [[Classification of Cronquist]] for traditional classification and [[Classification APG II]] for phylogenic classification

The oldest known fossils go back to a little more than 100 million years. It is thus about a young group, which quickly diversified. This group developed in an already rich environment, underwent a pressure of selection on behalf of many other groups (in particular animal) like the insects. This makes it possible to include/understand the astonishing adequacy which can exist between certain today angiospermes and certain animals (see concept of Coévolution). Angiospermes are traditionally classified in forty orders. One distinguishes various orders from old divergences, and two great units, the Monocotylédone S, which include inter alia the graminaceous (Blé, Maïs, Bambou), the date palm S or the plants with bulbs (Jonquille, Oignon, Poireau), and the true Dicotylédone S, which include the Chêne as well as the Potato, the Ortie S or the Artichaut S.

The history of botanical classifications shows that the systematicians try to approach an increasingly precise description of the vegetable groups according to the family ties between species. The last systems of classification published are that of Arthur Cronquist in 1981, used in many works, and more recently, that the Classification APG II (proposed by the Angiosperm Phylogeny Group) in 2003 founded on molecular phylogeny.

Importance for the man

One could not minimize the importance of Angiospermes for the human society. Not only they provide the majority of our Aliment S, directly (cereals, vegetables, fruits) or indirectly (poultry, animal feed), but still they provide, with certain Poacées (Bamboo…) and Euphorbiacées (Hévéa) a broad raw material diversity of which the use continued since the Neolithic era. Thus, they provide construction materials (wood, bamboo) that it is for the dwelling, transport (Bateau X, Brouette S), furniture or the tools; textile fibers (Cotton, flax), fuel (wood), fibers of cellulose (Paper), medicinal substances, dyes natural, elements of decorations (house plants, Gardening), etc

The selection and the intensive culture of Angiospermes are the field of the Agronomie, the Agriculture or the Sylviculture. And precisely, the Man completed a very rigorous work of selection to preserve the characters more the interesting one. Vast majority of the domesticated species present of the characters which the natural selection disadvantages. Indeed the Man primarily seeks to fix interesting characters (large fruits, beautiful flowers, many seeds, large tubers…) and in that it must be opposed to the very strong genetic mixing which carry out naturally Angiospermes. Also the Man thus tends to circumvent the systems supporting the cross-fertilization and to select the rare systems supporting self-fertilization (as the system baseds on the anatomy of the organized flower so that the autofecondation is obligatory: rolled up Hull, Cleistogamie selected at the corns Triticum and Chasmogamie). Have regard to the economic interest that the crop plants cause, the Man completed many research tasks to answer problems of output: “which are the means of obtaining a homogeneous descent of the same sex at dioïques species” when, at asparaguses for example, the male feet are systematically more productive, which gave place to the creation of the “super asparagus males” (a kind of equivalent of a genotype YY at the Man) able to give to a descent 100% male. Important work was undertaken with regard to the family of Moracées (Hop and Hemp) which it also generates an economic interest (legal or not) obvious.

It results from these processes of selection that the plants thus chosen by the Man are often homozygotes for all their couples of alleles (because born from a mode of self-fertilization maintained on a very great number of generations), even which they constitute quite simply a clone (together of individuals sharing the same genotype) as it was the case at the cultivated Potato Solanum tuberosum of which all the European cultures were in fact a clone at the 19th century. This involved a homogeneous answer vis-a-vis the mildew ( Phytophtora infestans ) and harvests were invariably destroyed. Polymorphism being the only response of the systems alive to the epidemics and the selective pressures, the monomorphism imposed by the Man for potato caused the destruction of harvests and the last great famine of the history in Europe, in particular in Ireland or almost 50% of the population found death, which supported a broad wave of immigration towards the United States.

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