Angiosperms (Angios- vessel, sperma- seeds)
Features of Angiosperms
Angiosperms are flowering plants, in which the flower is developed by ovule and pollen grain. Seeds are found always enclosed in fruits in angiosperms. These are the most familiar plant-like mango, peas, coconut, wheat, and rice.
The angiosperms diversified extensively during the Early Cretaceous (Cenozoic era), became widespread 120 million years ago, and replaced conifers as the dominant trees from 60 to 100 million years ago.
Habitats: As they are the largest group of plants they show a wide range of variation in habitat i.e. it may be hydrophytic, xerophytic, or mesophytic. halophytic etc.
Size: Size also shows wide ranges from the smallest Wolffia to tall trees like Eucalyptus (100 meters).
Uses of Angiosperms: they provide food, fodder, fuel, various medicines, and a variety of other commercial uses.
Classification of Angiosperms
Angiosperms are divided into two classes based on the number of cotyledons in seeds.
- Polypetalae– the sepals and petals are distinct, free petals, e.g. mustard, pea, etc.
- Gametopetalae – Sepals and petals are distinct, and petals are partially or completely fused. e.g. Sunflower, potato, etc.
- Monochalmydae– Incomplete due to the not distinct sepals and petals, e.g. cucumber.
Features of Dicotyledons
- In dicotyledons the seed-bearing two cotyledons.
- In these plants, reticulate venations are found in leaves.
- Flowers are tetramerous and pentamerous i.e. four or five members are found in each floral whorl.
Features of Monocotyledons
- These are characterized by only one cotyledon within the seed.
- Parallel venation is found in the leaves of monocotyledon.
- In each floral whorl, trimerous flowers i.e. three members in each flower whorl are found.
The life cycle of Angiosperms
Male sex organ in a flower: Stamen or microsporophyll
- The stamen consists of a slender filament bearing an anther on the tip.
- Under the anther, the Pollen mother cell undergoes meiosis producing microspores.
- Microspores mature into pollen grains.
Female sex organ in a flower: Pistil or carpel or megasporophyll
- In Pistil a swollen ovary at the base, a long slender style, and stigma are found.
- Ovules are present inside the ovary.
- In general, each ovule consists of a megaspore mother cell.
The mother cell undergoes meiosis producing four haploid megaspores, out of which three degenerate and one divides to form the embryo sac.
Each embryo sac consists of three egg apparatus: one egg cell and two Synergids, three antipodal cells, and two polar nuclei.
- A diploid secondary nucleus is formed by the fusion of polar nuclei.
Pollen grains disperse from anthers and are carried by various methods and agents like wind, water, and others to the stigma of the pistil, which is termed pollination.
- In the embryo sac, the pollen tube discharges two male gametes. From this, the one male gamete fuses with the egg cell (syngamy) and forms a zygote. Another male gamete fuses to the diploid secondary nucleus and produces a triploid primary endosperm nucleus (PEN).
The unique event double fertilization in Angiosperms:
Double fertilization: Here two fusions occur as syngamy and triple fusion, so the event is very important and termed double fertilization. This is a unique feature of angiosperms.
- With one or two cotyledons the zygote develops into an embryo and PEN develops as an endosperm. The endosperm provides nourishment to the developing embryo.
- After fertilization, the synergies and antipodals degenerate, the ovule develops into seeds and the ovaries develop into a fruit.
Read in detail: Sexual reproduction in flowering plants
Some importnat families of Angiosperms:
Fabaceae– (Papilionaceae) Pea family, which includes all pulses.
- Belongs to dicotyledons Angiosperms. The flowers are zygomorphic (The flower can be cut into two halves only through one radius), bisexual, and complete, the Calyx consists of five sepals, jointed.
- Corolla comprises five petals, polypetalous. A large petal is found called standard, two are smaller called wings, and two interior small, more or less jointed forms ‘keel’.
- Androecium contains ten stamens arranged in two whorls (9+1). The gynoecium is superior, monocarpellary, and uniocular with many ovules arranged on a marginal placenta. The fruit is a pod.
- Some examples of Fabaceae with the botanical name:
- Pea- Pisum sativum
- Arhar- Cajanus cajan
- Moong- Phaseolus aureus
- Lentil(masoor)- Lens culinaris
- Groundnut- Arachis hypogea
Malvaceae– China rose family
- These plants may be herbs, shrubs, or trees.
- The flowers are attractive, large, and generally solitary axillary.
- Pentamerous, actinomorphic flowers. (Actinomorphic- flower can be divided into two halves through any radius).
- Epicalyx is found as an additional whorl of bracteole below the calyx.
- five joint or free sepals are found at the base of the calyx.
- Corolla has five free petals.
- Indefinite numbers of monadelphous stamens are found in androecium.
- In Gynoecium 5 carpels are found, syncarpous, and superior ovary, axile placenta.
- The fruit is in the form of a capsule.
- Some other examples of this family are- cotton and ladyfinger.
Liliaceae– Lily family
- It belongs to monocot angiosperms. These are mostly perennial herbs.
- The rhizome or bulb-like stems are found.
- leaves may be fleshy, cauline i.e. arising from an underground stem.
- Bisexual, actinomorphic, trimerous, flowers are found in this family.
- Perianth is large, petaloid, and usually six, arranged in two whorls found the opposite to perianth lobes.
- Three carpels, syncarpous, superior ovary, axile placentation, and fruit are generally found as capsules.
- Examples of some common plants of Liliaceae with the botanical name
- Tulip- Tulipa tulip
- Lily- Lilium candidum
- Onium- Allium Cepa
Poaceae– Grass family including cereals.
- These belong to monocotyledons
- Flowers were found very small, inconspicuous, and had scale-like structures.
- Stamens are 3 in number, sometimes found 6 (rice and bamboo), 3 carpels, syncarpous uniocular, superior ovary with a basal ovule.
- Seedcoat and ovary wall found fused (caryopsis).
- Examples of some common plants of Poaceae with the botanical name:
- Rice- Oryza sativa
- Wheat- Triticum aestivum
- Maize- Zea mays
- Sugarcane- S. sponataneum
Economic importance of Flowering plants
In most of our food, cereals are used and these are obtained from flowering plants. Some examples are given below:
- Cereals: Triticum aestivum, Oryzae sativa, etc.
- Pulses: Cajanus cajan, Pisum sativum, etc.
- edible oil: Arachis hypogea, Brassica campestris, etc.
- Medicines: Aconitum napellus, Atropa belladona, etc.
- Beverages: Coffea arabica, Theobroma cacao, etc.
Hardwood and timber are also obtained from dicotyledonous trees example- teak, sal, oak, etc.
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