GROUPS (APG IV)
* Angiospermae Lindl.
* Magnoliophyta Cronquist ,
The ancestors of flowering plants diverged from gymnosperms in the
* 1 Description
* 1.1 Angiosperm derived characteristics * 1.2 Vascular anatomy * 1.3 Reproductive anatomy
* 2 Taxonomy
* 2.1 History of classification * 2.2 Modern classification * 2.3 Evolution
* 3 Flowering plant diversity
* 4 Ecology
* 5 Uses * 6 See also * 7 Notes * 8 References
* 9 Bibliography
* 9.1 Articles, books and chapters * 9.2 Websites
* 10 External links
ANGIOSPERM DERIVED CHARACTERISTICS
Bud of a pink rose
Distinctive features of
Flowers, the reproductive organs of flowering plants, are the most
remarkable feature distinguishing them from the other seed plants.
Flowers provided angiosperms with the means to have a more
species-specific breeding system, and hence a way to evolve more
readily into different species without the risk of crossing back with
related species. Faster speciation enabled the
Stamens with two pairs of pollen sacs Stamens are much lighter than the corresponding organs of gymnosperms and have contributed to the diversification of angiosperms through time with adaptations to specialized pollination syndromes, such as particular pollinators. Stamens have also become modified through time to prevent self-fertilization , which has permitted further diversification, allowing angiosperms eventually to fill more niches.
Reduced male parts, three cells The male gametophyte in angiosperms is significantly reduced in size compared to those of gymnosperm seed plants. The smaller size of the pollen reduces the amount of time between pollination — the pollen grain reaching the female plant — and fertilization . In gymnosperms, fertilization can occur up to a year after pollination, whereas in angiosperms, fertilization begins very soon after pollination. The shorter amount of time between pollination and fertilization allows angiosperms to produce seeds earlier after pollination than gymnosperms, providing angiosperms a distinct evolutionary advantage.
Closed carpel enclosing the ovules (carpel or carpels and accessory parts may become the fruit ) The closed carpel of angiosperms also allows adaptations to specialized pollination syndromes and controls. This helps to prevent self-fertilization, thereby maintaining increased diversity. Once the ovary is fertilized, the carpel and some surrounding tissues develop into a fruit. This fruit often serves as an attractant to seed-dispersing animals. The resulting cooperative relationship presents another advantage to angiosperms in the process of dispersal .
Reduced female gametophyte, seven cells with eight nuclei The reduced female gametophyte, like the reduced male gametophyte, may be an adaptation allowing for more rapid seed set, eventually leading to such flowering plant adaptations as annual herbaceous life-cycles, allowing the flowering plants to fill even more niches.
Endosperm In general, endosperm formation begins after fertilization and before the first division of the zygote . Endosperm is a highly nutritive tissue that can provide food for the developing embryo , the cotyledons , and sometimes the seedling when it first appears.
The amount and complexity of tissue-formation in flowering plants exceeds that of gymnosperms. The vascular bundles of the stem are arranged such that the xylem and phloem form concentric rings.
In the dicotyledons, the bundles in the very young stem are arranged in an open ring, separating a central pith from an outer cortex. In each bundle, separating the xylem and phloem, is a layer of meristem or active formative tissue known as cambium . By the formation of a layer of cambium between the bundles (interfascicular cambium), a complete ring is formed, and a regular periodical increase in thickness results from the development of xylem on the inside and phloem on the outside. The soft phloem becomes crushed, but the hard wood persists and forms the bulk of the stem and branches of the woody perennial. Owing to differences in the character of the elements produced at the beginning and end of the season, the wood is marked out in transverse section into concentric rings, one for each season of growth, called annual rings .
Among the monocotyledons, the bundles are more numerous in the young stem and are scattered through the ground tissue. They contain no cambium and once formed the stem increases in diameter only in exceptional cases.
The characteristic feature of angiosperms is the flower. Flowers show remarkable variation in form and elaboration, and provide the most trustworthy external characteristics for establishing relationships among angiosperm species. The function of the flower is to ensure fertilization of the ovule and development of fruit containing seeds . The floral apparatus may arise terminally on a shoot or from the axil of a leaf (where the petiole attaches to the stem). Occasionally, as in violets , a flower arises singly in the axil of an ordinary foliage-leaf. More typically, the flower-bearing portion of the plant is sharply distinguished from the foliage-bearing or vegetative portion, and forms a more or less elaborate branch-system called an inflorescence .
There are two kinds of reproductive cells produced by flowers. Microspores, which will divide to become pollen grains , are the "male" cells and are borne in the stamens (or microsporophylls). The "female" cells called megaspores, which will divide to become the egg cell (megagametogenesis ), are contained in the ovule and enclosed in the carpel (or megasporophyll).
The flower may consist only of these parts, as in willow , where each
flower comprises only a few stamens or two carpels. Usually, other
structures are present and serve to protect the sporophylls and to
form an envelope attractive to pollinators. The individual members of
these surrounding structures are known as sepals and petals (or tepals
in flowers such as
While the majority of flowers are perfect or hermaphrodite (having both pollen and ovule producing parts in the same flower structure), flowering plants have developed numerous morphological and physiological mechanisms to reduce or prevent self-fertilization. Heteromorphic flowers have short carpels and long stamens, or vice versa, so animal pollinators cannot easily transfer pollen to the pistil (receptive part of the carpel). Homomorphic flowers may employ a biochemical (physiological) mechanism called self-incompatibility to discriminate between self and non-self pollen grains. In other species, the male and female parts are morphologically separated, developing on different flowers.
HISTORY OF CLASSIFICATION
From 1736, an illustration of Linnaean classification
The botanical term "Angiosperm", from the Ancient Greek αγγείον, angeíon (bottle, vessel) and σπέρμα, (seed), was coined in the form Angiospermae by Paul Hermann in 1690, as the name of one of his primary divisions of the plant kingdom . This included flowering plants possessing seeds enclosed in capsules, distinguished from his Gymnospermae, or flowering plants with achenial or schizo-carpic fruits, the whole fruit or each of its pieces being here regarded as a seed and naked. The term and its antonym were maintained by Carl Linnaeus with the same sense, but with restricted application, in the names of the orders of his class Didynamia . Its use with any approach to its modern scope became possible only after 1827, when Robert Brown established the existence of truly naked ovules in the Cycadeae and Coniferae , and applied to them the name Gymnosperms. From that time onward, as long as these Gymnosperms were, as was usual, reckoned as dicotyledonous flowering plants, the term Angiosperm was used antithetically by botanical writers, with varying scope, as a group-name for other dicotyledonous plants. An auxanometer , a device for measuring increase or rate of growth in plants
In 1851, Hofmeister discovered the changes occurring in the embryo-sac of flowering plants, and determined the correct relationships of these to the Cryptogamia . This fixed the position of Gymnosperms as a class distinct from Dicotyledons, and the term Angiosperm then gradually came to be accepted as the suitable designation for the whole of the flowering plants other than Gymnosperms, including the classes of Dicotyledons and Monocotyledons. This is the sense in which the term is used today.
In most taxonomies, the flowering plants are treated as a coherent group. The most popular descriptive name has been Angiospermae (Angiosperms), with Anthophyta ("flowering plants") a second choice. These names are not linked to any rank. The Wettstein system and the Engler system use the name Angiospermae, at the assigned rank of subdivision. The Reveal system treated flowering plants as subdivision Magnoliophytina (Frohne "> Monocot (left) and dicot seedlings
Traditionally, the flowering plants are divided into two groups,
which in the
Cronquist system are called
Magnoliopsida (at the rank
of class, formed from the family name Magnoliaceae) and
the rank of class, formed from the family name
Recent studies, as by the APG, show that the monocots form a
monophyletic group (clade ) but that the dicots do not (they are
paraphyletic ). Nevertheless, the majority of dicot species do form a
monophyletic group, called the eudicots or tricolpates . Of the
remaining dicot species, most belong to a third major clade known as
the magnoliids , containing about 9,000 species. The rest include a
paraphyletic grouping of early branching taxa known collectively as
the basal angiosperms , plus the families
There are eight groups of living angiosperms:
Amborella , a single species of shrub from
Chloranthales , several dozen species of aromatic plants with
Magnoliids , about 9,000 species, characterized by trimerous
flowers, pollen with one pore, and usually branching-veined
leaves—for example magnolias , bay laurel , and black pepper ;
Monocots , about 70,000 species, characterized by trimerous
flowers, a single cotyledon , pollen with one pore, and usually
parallel-veined leaves—for example grasses , orchids , and palms ;
Ceratophyllum , about 6 species of aquatic plants , perhaps most
familiar as aquarium plants;
The exact relationship between these eight groups is not yet clear,
although there is agreement that the first three groups to diverge
from the ancestral angiosperm were
2. Example of alternative phylogeny (2010)
basal angiosperms core angiosperms
3. APG IV (2016)
DETAILED CLADOGRAM OF THE ANGIOSPERM PHYLOGENY GROUP (APG) IV CLASSIFICATION.
Amborellales Melikyan, Bobrov border-left:1px solid;vertical-align:top;text-align:center;">
Chloranthales Mart. 1835
Canellales Cronquist 1957
Piperales von Berchtold vertical-align:top;text-align:center;">
Laurales de Jussieu ex von Berchtold vertical-align:top;text-align:center;">
Acorales Link 1835
Asparagales Link 1829
Arecales Bromhead 1840
Poales Small 1903
Ceratophyllales Link 1829
Ranunculales de Jussieu ex von Berchtold border-left:1px solid;vertical-align:top;text-align:center;">
Proteales de Jussieu ex von Berchtold border-left:1px solid;vertical-align:top;text-align:center;">
Saxifragales von Berchtold border-left:1px solid;vertical-align:top;text-align:center;">
Vitales de Jussieu ex von Berchtold border-left:1px solid;vertical-align:top;text-align:center;">
Zygophyllales Link 1829
Celastrales Link 1829
Oxalidales von Berchtold border-left:1px solid;vertical-align:top;text-align:center;">
Malpighiales de Jussieu ex von Berchtold vertical-align:top;text-align:center;">
Fabales Bromhead 1838
Rosales von Berchtold border-left:1px solid;vertical-align:top;text-align:center;">
Cucurbitales de Jussieu ex von Berchtold border-left:1px solid;vertical-align:top;text-align:center;">
Myrtales de Jussieu ex von Berchtold vertical-align:top;text-align:center;">
Picramniales Doweld 2001
Sapindales de Jussieu ex von Berchtold border-left:1px solid;vertical-align:top;text-align:center;">
Huerteales Doweld 2001
Malvales de Jussieu ex von Berchtold border-left:1px solid;vertical-align:top;text-align:center;">
Brassicales Bromhead 1838
Cornales Link 1829
Ericales von Berchtold border-left:1px solid;vertical-align:top;text-align:center;">
Icacinales Van Tieghem 1900
Garryales Mart. 1835
Gentianales de Jussieu ex von Berchtold border-left:1px solid;vertical-align:top;text-align:center;">
Solanales de Jussieu ex von Berchtold border-left:1px solid;vertical-align:top;text-align:center;">
Boraginales de Jussieu ex von Berchtold border-left:1px solid;vertical-align:top;text-align:center;">
Vahliales Doweld 2001
Lamiales Bromhead 1838
Escalloniales Mart. 1835
Asterales Link 1829
Bruniales Dumortier 1829
Evolutionary history of plants
Fossilized spores suggest that higher plants (embryophytes ) have
lived on land for at least 475 million years. Early land plants
reproduced sexually with flagellated, swimming sperm, like the green
algae from which they evolved. An adaptation to terrestrialization was
the development of upright meiosporangia for dispersal by spores to
new habitats. This feature is lacking in the descendants of their
nearest algal relatives, the Charophycean green algae. A later
terrestrial adaptation took place with retention of the delicate,
avascular sexual stage, the gametophyte, within the tissues of the
vascular sporophyte. This occurred by spore germination within
sporangia rather than spore release, as in non-seed plants. A current
example of how this might have happened can be seen in the precocious
spore germination in
The apparently sudden appearance of nearly modern flowers in the
fossil record initially posed such a problem for the theory of
Charles Darwin called it an "abominable mystery".
However, the fossil record has considerably grown since the time of
Darwin, and recently discovered angiosperm fossils such as
Archaefructus , along with further discoveries of fossil gymnosperms,
suggest how angiosperm characteristics may have been acquired in a
series of steps. Several groups of extinct gymnosperms, in particular
seed ferns , have been proposed as the ancestors of flowering plants,
but there is no continuous fossil evidence showing exactly how flowers
evolved. Some older fossils, such as the upper
The evolution of seed plants and later angiosperms appears to be the result of two distinct rounds of whole genome duplication events. These occurred at 319 million years ago and 192 million years ago . Another possible whole genome duplication event at 160 million years ago perhaps created the ancestral line that led to all modern flowering plants. That event was studied by sequencing the genome of an ancient flowering plant, Amborella trichopoda , and directly addresses Darwin's "abominable mystery."
The earliest known macrofossil confidently identified as an
Archaefructus liaoningensis , is dated to about 125
million years BP (the
In 2013 flowers encased in amber were found and dated 100 million years before present. The amber had frozen the act of sexual reproduction in the process of taking place. Microscopic images showed tubes growing out of pollen and penetrating the flower's stigma. The pollen was sticky, suggesting it was carried by insects.
The great angiosperm radiation , when a great diversity of
angiosperms appears in the fossil record, occurred in the
It is generally assumed that the function of flowers, from the start, was to involve mobile animals in their reproduction processes. That is, pollen can be scattered even if the flower is not brightly colored or oddly shaped in a way that attracts animals; however, by expending the energy required to create such traits, angiosperms can enlist the aid of animals and, thus, reproduce more efficiently.
Island genetics provides one proposed explanation for the sudden, fully developed appearance of flowering plants. Island genetics is believed to be a common source of speciation in general, especially when it comes to radical adaptations that seem to have required inferior transitional forms. Flowering plants may have evolved in an isolated setting like an island or island chain, where the plants bearing them were able to develop a highly specialized relationship with some specific animal (a wasp , for example). Such a relationship, with a hypothetical wasp carrying pollen from one plant to another much the way fig wasps do today, could result in the development of a high degree of specialization in both the plant(s) and their partners. Note that the wasp example is not incidental; bees , which, it is postulated, evolved specifically due to mutualistic plant relationships, are descended from wasps.
Animals are also involved in the distribution of seeds.
A few paleontologists have also proposed that flowering plants, or angiosperms, might have evolved due to interactions with dinosaurs. One of the idea's strongest proponents is Robert T. Bakker . He proposes that herbivorous dinosaurs, with their eating habits, provided a selective pressure on plants, for which adaptations either succeeded in deterring or coping with predation by herbivores.
FLOWERING PLANT DIVERSITY
The number of species of flowering plants is estimated to be in the
range of 250,000 to 400,000. This compares to around 12,000 species
of moss or 11,000 species of pteridophytes , showing that the
flowering plants are much more diverse. The number of families in APG
(1998) was 462. In
The diversity of flowering plants is not evenly distributed. Nearly all species belong to the eudicot (75%), monocot (23%), and magnoliid (2%) clades. The remaining 5 clades contain a little over 250 species in total; i.e. less than 0.1% of flowering plant diversity, divided among 9 families. The 42 most-diverse of 443 families of flowering plants by species, in their APG circumscriptions, are
Of these, the Orchidaceae, Poaceae, Cyperaceae, Arecaceae, and Iridaceae are monocot families; Piperaceae, Lauraceae, and Annonaceae are magnoliid dicots; the rest of the families are eudicots.
FERTILIZATION AND EMBRYOGENESIS
FRUIT AND SEED
As the development of embryo and endosperm proceeds within the embryo sac, the sac wall enlarges and combines with the nucellus (which is likewise enlarging) and the integument to form the seed coat. The ovary wall develops to form the fruit or pericarp , whose form is closely associated with the manner of distribution of the seed.
Frequently, the influence of fertilization is felt beyond the ovary , and other parts of the flower take part in the formation of the fruit, e.g., the floral receptacle in the apple , strawberry , and others.
The character of the seed coat bears a definite relation to that of the fruit. They protect the embryo and aid in dissemination; they may also directly promote germination. Among plants with indehiscent fruits, in general, the fruit provides protection for the embryo and secures dissemination. In this case, the seed coat is only slightly developed. If the fruit is dehiscent and the seed is exposed, in general, the seed-coat is well developed, and must discharge the functions otherwise executed by the fruit.
Flowering plants generate gametes using a specialized cell division called meiosis . Meiosis takes place in the ovule (a structure within the ovary that is located within the pistil at the center of the flower) (see diagram labeled "Angiosperm lifecycle"). A diploid cell (megaspore mother cell ) in the ovule undergoes meiosis (involving two successive cell divisions) to produce four cells (megaspores or female gametes) with haploid nuclei. One of these four cells (megaspore) then undergoes three successive mitotic divisions to produce an immature embryo sac (megagametocyte) with eight haploid nuclei. Next, these nuclei are segregated into separate cells by cytokinesis to producing 3 antipodal cells, 2 synergid cells and an egg cell. Two polar nuclei are left in the central cell of the embryo sac.
Pollen is also produced by meiosis in the male anther (microsporangium ). During meiosis, a diploid microspore mother cell undergoes two successive meiotic divisions to produce 4 haploid cells (microspores or male gametes). Each of these microspores, after further mitoses, becomes a pollen grain (microgametophyte) containing two haploid generative (sperm) cells and a tube nucleus. When a pollen grain makes contact with the female stigma, the pollen grain forms a pollen tube that grows down the style into the ovary. In the act of fertilization, a male sperm nucleus fuses with the female egg nucleus to form a diploid zygote that can then develop into an embryo within the newly forming seed . Upon germination of the seed, a new plant can grow and mature.
The adaptive function of meiosis is currently a matter of debate. A
key event during meiosis in a diploid cell is the pairing of
homologous chromosomes and homologous recombination (the exchange of
genetic information) between homologous chromosomes. This process
promotes the production of increased genetic diversity among progeny
and the recombinational repair of damages in the
In some parts of the world, certain single species assume paramount
importance because of their variety of uses, for example the coconut
(Cocos nucifera ) on Pacific atolls , and the olive (Olea europaea )
Flowering plants also provide economic resources in the form of wood
, paper , fiber (cotton , flax , and hemp , among others), medicines
(digitalis , camphor ), decorative and landscaping plants, and many
other uses. The main area in which they are surpassed by other plants
— namely, coniferous trees (
* ^ The major exception to the dominance of terrestrial ecosystems by flowering plants is the coniferous forest .
* ^ A B C APG 2016 .
* ^ Cronquist 1960 .
Takhtajan 1964 .
* ^ Lindley, J (1830). Introduction to the Natural System of
Botany. London: Longman, Rees, Orme, Brown, and Green. xxxvi.
* ^ Cantino, Philip D.; Doyle, James A.; Graham, Sean W.; Judd,
Walter S.; Olmstead, Richard G.; Soltis, Douglas E. ; Soltis, Pamela
S. ; Donoghue, Michael J. (2007). "Towards a phylogenetic nomenclature
of Tracheophyta". Taxon. 56 (3): E1–E44. doi :10.2307/25065865 .
* ^ Cronquist (1988). Magnoliophyta Flowering Plants.
* ^ Christenhusz, M. J. M.; Byng, J. W. (2016). "The number of
known plants species in the world and its annual increase". Phytotaxa.
ARTICLES, BOOKS AND CHAPTERS
* APG (2003). "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG II". Botanical Journal of the Linnean Society . 141 (4): 399–436. doi :10.1046/j.1095-8339.2003.t01-1-00158.x . * APG (2009). "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III". Botanical Journal of the Linnean Society . 161 (2): 105–121. doi :10.1111/j.1095-8339.2009.00996.x . Retrieved 2010-12-10. * APG (2016). "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV". Botanical Journal of the Linnean Society . 181 (1): 1–20. doi :10.1111/boj.12385 . Retrieved 2016-05-20. * Becker, Kenneth M. (February 1973). "A Comparison of Angiosperm Classification Systems". Taxon . 22 (1): 19–50. doi :10.2307/1218032 .
* Bell, Adrian D. (2008) .
* 1st edition ISBN 9780198542193
* Bell, C.D.; Soltis, D.E. ; Soltis, P.S. (2010). "The Age and
Diversification of the