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ANGIOSPERMS {FLOWERING PLANTS}. GENERAL CHARACTERISTICS. Dr. Anurita Sharma Assistant Professor Department of Botany Post Graduate Govt. College For Girls Sector-11, Chandigarh.
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ANGIOSPERMS {FLOWERING PLANTS} GENERAL CHARACTERISTICS Dr. Anurita Sharma Assistant Professor Department of Botany Post Graduate Govt. College For Girls Sector-11, Chandigarh
Angiosperm means "contained seeds“ , the ovules are sealed within the carpel and the seeds sealed within a fruit.
The flowering plants or angiosperms emerged in the Cretaceous period, some 130 million years ago. These sporophytes dominate the landscape around us and are the most successful plant group, with something like a quarter of a million species described.
Plant body is divided into true roots, stem and leaves. • Sporophytic generation is the dominant phase represented by the plant body. • Gametophytic generation is reduced and is totally dependent on sporophyte. • Flowers display plant’s male and female parts and are sites of pollination and fertilization. • Generate fruits, which contain seeds.
Most of the Angiosperms are autotrophic and have a green pigment chlorophyll for photosynthesis. • A few species lack chlorophyll and become parasitic, e.g., Cuscuta , Viscum. • Some plants are insectivorous, e.g., Nepenthes, Drosera.
INSECTIVOROUS PLANTS Drosera (Sundew) Nepenthes ( Pitcher plant)
Based on habitat Angiosperms are mainly of three types: • Hydrophytes: • These plants grow in aquatic habitats. They have developed aerenchyma and a covering of mucilage. They may be submerged or floating . • Mesophytes: • These are terrestrial plants growing under moderate moisture temperate conditions. • Xerophytes: • These are terrestrial plants of dry habitat. They develop adaptations to reduce transpiration and to retain water.
HYDROPHYTES Lemna Hydrilla Nymphaea
Mesophytes Sunflower Petunia
XEROPHYTES Opuntia Nerium
Duration and Habit Duration- the life span of an individual plant. Annual- plants live for a single growing season; Biennial- lives for two seasons; Perennial- lives for three or more years and usually flowers and fruits repeatedly. Habit- the general appearance of a plant. Tree- plant with woody tissue present in one primary trunk; Shrub- plant with woody tissue present in several trunks and usually shorter than trees; Herb- plant lacking woody tissue; Liana- climbing plant with woody stems; Vine- climbing plants with herbaceous (non- woody) stems.
Angiosperms (Flowering Plants) Systematists have identified angiosperms into two sub- groups: Monocotyledonous and dicotyledonous. Monocotsare angiosperms that possess one embryonic seed leaf (cotyledon). Dicotsare angiosperms that possess two embryonic seed leaves (cotyledons).
The vegetativeparts of angiosperms are roots, stems, and leaves, and the reproductiveparts are flowers, fruits, and seeds. Here we outline parts, particularly as they refer to angiosperms.
Roots Adventitious- developing from any plant part other than the embryonic root or another root. Fibrous- with all portions of the root system being of more or less equal thickness, often well branched. Taproot- the major root, usually enlarged and growing downward.
Stems Stem —the axis of plants—consists of nodes (where leaves and axillary buds are produced) separated by internodes.
Node -region of the stem where the leaf and bud are borne. Internode -the part of the stem between two adjacent nodes. Herbaceous -not woody; dying down at the end of the growing season. Woody- hard in texture, containing secondary xylem, and persisting more than one growing season. Acaulescent -having an inconspicuous stem. Caulescent -having a distinct stem.
Bulb- a short, erect, underground stem surrounded by thick, fleshy leaves or leaf bases. Corm- a short, erect, underground, more or less fleshy stem covered with thin, dry leaves or leaf bases. Rhizome -a horizontal stem, more or less underground, bearing scale-like leaves; often called a stolon if above ground and having an elongated internode. Scape -an erect leafless stem bearing an inflorescence or flower. Thorn -a reduced, sharp-pointed stem. Tuber -a swollen, fleshy portion of a rhizome involved in water or carbohydrate storage.
Buds Budsare short embryonic stems. In angiosperms they are found at the nodes, in the leaf axil(the angle formed by the stem and the petiole of the leaf). Axillary bud - a bud located in the leaf axil. Terminal bud- a bud at the apex of a stem.
Leaves Leavesare the major photosynthetic parts of most plants. They are borne at the nodes of a stem, usually below a bud. They are usually flat, and have one surface facing towards the stem axis (theadaxial, or upper, surface) and another surface facing away from the stem axis (the abaxial, or lower, surface). Leaves are homologous structures among the angiosperms, but not among vascular plants as a whole. In addition to the obvious function in photosynthesis, leaves may be modified for protection, forming sharp pointed spines; for water storage, as in many succulents; for climbing, as in vines and lianas with tendril leaves; for capturing insects, as in carnivorous plants; or providing homes for ants or mites.
The major parts of the leaf are shown below. In monocots the leaf is almost always broadly sheathing at the base. In taxa such as grasses and gingers there is an adaxial flap or ligule at the junction of the sheath and blade.A leaf thatlacks a petiole is said to be sessile.
Pulvini (singular pulvinus) - somewhat swollen and morphologically distinct parts of the petiole, are often present and involved in leaf movement. Stipules -usually paired appendages located on either side of (or on) the petiole base.
Leaf Arrangement- Leaves may be arranged in one of three major patterns: Alternate leavesare arranged singly and are usually arranged in a spiral pattern along the stem. Alternate leaves are sometimes placed along just two sides of the stem (2-ranked, or distichous), or only three sides of the stem (3-ranked, or tristichous). Opposite leavesare borne in pairs, the members of which are positioned on opposite sides of the stem. A common pattern for opposite leaves is for each successive set of paired leaves to be rotated 90 degrees (decussate). When three or more leaves are positioned at a node, they are considered to be whorled.
Leaf Structure- A leaf with a single blade is termedsimple; a leaf with two or more blades, or leaflets, is said to be compound. The distinction between simple and compound leaves can be made by locating the axillary bud: an axillary bud is subtended by an entire leaf and never by individual leaflets. Leaflets can be arranged in various ways, including even-pinnate, odd-pinnate, palmate, trifoliate, and twice-pinnate.
Leaf Duration- Leaves may function from a few days to many years, but most leaves function for only one or two growing seasons. Deciduousleaves fall at the end of the growing season;evergreenplants are leafy throughout the year. Venation Types- If there is one most prominent vein in a leaf, it is called the midvein or primary vein; branches from this vein are called secondary veins. Tertiary veins usually link the secondaries, forming a ladderlike or netlike (reticulate) pattern.
There are three major patterns of organization of the major veins. The leaf may have a single primary vein with the secondary veins arising along its length like the teeth of a comb; this pattern is termed pinnate.Or the leaf may have several major veins radiating from the base of the blade; this pattern is called palmate. Finally, the leaf may have many parallel veins, a pattern termedparallelvenation.
An important characteristic of Angiosperms is a flower. It is a modified condensed shoot meant essentially for the reproduction of the plant. • The flower arises in the axil of a leaf supported by a stalk called as pedicel. • The upper swollen end of the pedicel called as receptacle or torus or thalamus bears all the floral parts. • A flower consists of four whorls of floral leaves – calyx, corolla, androecium and gynoecium. • Calyxandcorollaare sterile, non-essential accessory whorls. • Androeciumandgynoeciumare fertile, essentialreproductive whorls.
Flower-sepals, petals, stamens, carpels. Sepal (calyx)-before flower opens, sepals enclose and protect flower bud. Petal (corolla) -advertises flower to insects and other pollinators. Flower’sreproductive organs: stamen and carpel. Stamen (androecium) -male organ. Carpel (gynoecium) -female organ. Ovary-base of the carpel. Houses ovules. Ovule-contains developing egg and cells that support it.
In the simplest flowers the parts are arranged successively - calyx, corolla, androecium, gynoecium (hypogynous flower, superior ovary). In some flowers (Rosaceae) the receptacle grows up around the ovary into a kind of cup (perigynous flower, superior ovary) and in others the other parts are joined to the top of the ovary (epigynous flower, inferior ovary).
DOUBLE FERTILIZATION Refers to a process in which two sperm cells fertilize cells in the ovary. This process begins when a pollen grain adheres to the stigma of the pistil (female reproductive structure), germinates, and grows a long pollen tube. While this pollen tube is growing, a haploid generative cell travels down the tube behind the tube nucleus. The generative cell divides by mitosis to produce two haploid (n) sperm cells.
The pollen tube enters into the ovule, through the micropyle. Inside the embryo sac, the tip of the pollen tube ruptures and the 2 male gametes are set free near the egg apparatus. Inside the embryo sac, one of the 2 male gametes fuses with the egg nucleus and forms a diploid zygote.This process is called syngamyortrue fertilisation. The other male gamete pushes further into the embryo sac and fuses with the secondary nucleus and gives rise to a triploid nucleus called the primary endosperm nucleus. This process of nuclear fusion is calledtriple fusion.
DOUBLE FERTILIZATION This entire phenomenon of fertilisation involving the fusion of the egg and one of the male gametes, together with the union of the second male gamete with the secondary nucleus or the polar nuclei is called as double fertilisation.
As the zygote develops into an embryo, the triploid cell develops into the endosperm, which serves as the embryo's food supply. The ovary now will develop into fruit and the ovule will develop into seed.
Features that enhanced success of angiosperms • Evolution of mutually dependent relationships with animals (carry pollen more reliably then wind). • Ability to reproduce rapidly (fertilization occurs 12 hours after pollination, making it possible for plant to produce seeds in few days or weeks).
INTERACTIONS WITH ANIMALS-PROFOUNDLY INFLUENCED ANGIOSPERM EVOLUTION • Flowering plants and land animals have mutually beneficial relationships throughout their evolutionary history. • Most angiosperms depend on birds, insects and mammals for pollination and seed dispersal. • Most land animals depend on angiosperms for food. • Mutual dependency improves reproductive success of both and thus is favoured by natural selection.
Bees are attracted to flowers that have markings that reflect UV light. As bee feeds on nectar, it picks up pollen.
Flowers that attract hummingbirds have nectar located deep in floral tube where only the long, thin beak and tongue of that bird can reach.Picks up pollen on beak and feather while feeding.
Some flowering plants depend on nocturnal pollinators such as bats. These plants have large, light-coloured highly scented flowers that can be easily found at night. Anther dusts bat’s hair with pollen and passes onto other flowers.
