Notes on Morphology of Flowering Plants for NEET 2022 Biology

Evolution has given the world unbelievable variations that have fascinated scientists forever. Organisms are capable of displaying the most vivid structural diversity. To study and understand the process behind this development, one needs to consider both the similarities and differences. Morphology is the branch of science that deals with the study of the organisms’ structure, characteristics, and forms. 

The chapter Morphology of flowering plants is an important concept while preparing for NEET 2022 Biology.

Importance of morphology

• Assigns a fixed contour to the body type.
• Obtain information about homology and analogy of organs.
• Determine structural data.
• Recognise and classify organisms based on external morphology.
• Form a basis for the division of organisms.
• Observe changes induced by environmental factors.
• Study the offensive and defensive organs.

Plants have been a part of human life since the beginning of life. They have provided us with food, oxygen, shelter, resources, and many other things. The flower-bearing plants, known scientifically as angiosperms, have been integral to our culture. They are believed to have evolved from gymnosperms during the Triassic period, with the first flowering plant having emerged about 140 million years ago. Flowering plants have the most variety in their 300,000 known species.

Let us gain a deeper insight into the morphology of flowering plants.

Roots

The underground parts of the vascular plants are termed roots. The primary function of the roots is to obtain the essential minerals, nutrients, and water from the soil. Also, they serve as an anchor for the plant. Although not every plant has its roots underground, some also have them above the ground, known as aerial roots. They also serve the same purpose by fixing the plants to nearby structures like walls, rocks, trellises, etc. Some plants with aerial roots are Bansai, Banyan Tree, and Mangroves.

Kinds of Roots

Taproot System: They develop from the radical of germinating seed along with the primary roots and branches. Majorly they are found in the dicotyledonous plants. Some examples include mustard seed, mangoes, grams, and banyan.

Fibrous root system: This root system develops from primary or thin and moderately branching roots growing from the stem. Normally they don’t penetrate deeply into the soil. This gives them a mat or carpet-like appearance on reaching full maturity. Such root systems are mainly observed in fens and monocotyledonous plants. Some examples include wheat, paddy, grass, carrots, and onions.

Adventitious root System: Roots originate from any part of the plant body apart from the radicle. This root system serves various purposes like mechanical support and vegetative propagation. Monocotyledonous plants are seen to have this root system. Some examples include the banyan tree, maize, oak tree, and horsetails.

Functions

Roots are responsible for performing some of the essential functions needed for the survival of plants.

• Anchoring: They help attach the plant to the ground and help keep them erect.
• Absorption: They act as the supplier of water and dissolved minerals from the soil needed for important processes like photosynthesis.
• Storage: Extra food is converted to starch and stored in the roots. Some examples include carrots, radish, and beetroot.
• Reproduction: They also function as a means of reproduction in certain plants, termed vegetative propagation. New plants arise from creeping horizontal stems called runners (stolons). Some examples include jasmine and grass.
• Ecological Function: They benefit the environment by preventing soil erosion and giving sustenance and habitat to other organisms.

Also See: Anatomy of Flowering Plants 

Regions

• The Root Cap
• The region of Maturation
• The region of Elongation

Modifications

• Storage: Taproots in carrot and turnip, and adventitious roots in sweet potato change for food storage.
• Support: Prop roots arise from the branches in the case of the banyan tree. Stilt root also comes out of lower stem nodes in the case of sugarcane.
• Aeration: Pneumatophores in mangroves aid them in respiration in swampy areas. In the case of Rhizophora, the roots grow above the ground to help in this.
• Nitrogen fixation: Root nodules of the leguminous plants help fix the free nitrogen present in the air.

Shoot System

Stems are the ascending part of the plant axis that bears branches, leaves, flowers, fruits and is responsible for transporting waters and minerals. It is developed from the plumule of the embryo or germinating seeds. They stay above the ground and are green in youth and later turn brown and woody with age.

Characteristics

• Develops from the plumule and epicotyl of the embryo
• Stands erect and grow away from the soil towards the light
• Terminal bud at the apex of the stem
• In angiosperms, the shoot is differentiated into nodes and internodes
• Young stems are green and photosynthetic
• Presence of multicellular hair
• Stem and branches of mature plants bear fruits and flowers

Modification

• Underground Stem: Helps plants sustain and grow in unfavorable conditions
• Rhizome: Runs parallel to the ground and has nodes, internodes, and buds. Examples include ginger and banana.
• Tubers: Swollen end part like in potato
• Corm: Grows vertically below the ground like in colocasia
• Bulb: Reduced stem protected by scaly leaves. Examples include garlic and onions.
• Stem Tendrils: Coiled structure for supporting tender stems of the plant and helping in climbing. Examples include grapes, cucumber, and pumpkin.
• Thorn: To protect against grazing animals, the axillary bud is modified into pointed thorns. Examples include Bougainvillaea and citrus.

Sub Aerial Weak Stem

• Offsets: Rosette of leaves from the decrease in internodes of lateral branches. Examples include Eichhornia and Pistia.
• Suckers: Lateral branches arise from the underground portion of the stem. Examples include Chrysanthemum, Banana, and Pineapple.
• Runners: Stem runs horizontally above the ground, and roots arise at nodes. Examples include grasses and strawberries.
• Stolon: Lateral branches arise normally but then bend down and touch the soil where the root grows, and the new daughter plant appear like in the case of mint

Aerial modification: The stem is completely metamorphosed for various adaptations, e.g. Phylloclade of xerophytes plants. The stem becomes fleshy and green, having photosynthetic pigments to prepare food as leaves are reduced to thorns to check water loss by transpiration, e.g. Euphorbia, Opuntia.

Leaves

Leaves are a laterally borne structure and are normally flattened. The main parts of the leaf are the leaf base, petiole, and lamina. They contain a green pigment known as chlorophyll that helps in photosynthesis. They also have tiny pores or openings called stomata, where they exchange gas.

Characteristics

• Arises from the node
• Exogenous in origin
• Bud at its axis
• Limited growth
• No apical bud

Venation

• Reticulate: An irregularly distributed network of veins found in dicotyledons.
• Parallel: Parallel network of veins found in monocotyledons.

Types

• Simple: Complete lamina and incision does not reach the midrib
• Compound: Incision touches midrib and divides the leaf into several leaflets
• Pinnately compound: Leaflets are present on the common axis known as midrib, called the rachis. Example: Neem.
• Palmately compound: Leaflets are attached at the petiole tip. Example: silk cotton.

Phyllotaxy

The pattern of arrangement of leaves around the stem.

• Alternate type: Single leaf present at each node. Examples include Hibiscus and Brassica
• Opposite type: Each node bears a pair of leaves. Examples include Psidium guajava and Calotropis.
• Whorled type: More than two leaves arise at the node to form a whorl. Example: Alstonia.

Modifications

• Tendrils: To support climbers, the leaves modify to form a long thread-like structure. Example: peas.
• Spine: For reduced water loss in xerophytic plants. Examples include cactus and aloe.
• Storage: Changes for the accommodation of extra food. Examples include garlic and onion.
• Phyllodes: Petiole modified to form a leaf-like structure and function. Example: Acacia.
• Pitcher: In the pitcher plant, the leaf modifies to trap insects.

Functions

• Photosynthesis
• Transpiration
• Storage
• Guttation
• Defence

Inflorescence

Flower arrangement around the floral axis.

• Racemose: Flowers are arranged laterally in acropetal succession, i.e. older flowers at the bottom and the younger ones at the top. The main axis grows indefinitely. Examples include raceme, spike, umbel, capitulum, corymb, catkin, and spadix.
• Cymose: Flowers are arranged in a basipetal order, i.e. older flowers are at the top, and new flowers are at the bottom. The main axis has limited growth that terminates in flowers. Examples include monochasial cyme and dichasial cyme.

Special types of inflorescence

• Verticillaster: Sessile flowers arranged in a dichasial cyme. Examples include Ocimum and Salvia.
• Cyathium: Involucre of bracts form cup shape structure, single female flower is surrounded by numerous male flowers. Example: Euphorbia
• Hypanthium: both male and female flowers are present in a cavity with an apical opening called the ostiole. Example: Fig.

Flowers

Flowers are the reproductive parts of the plant. It has four whorls: calyx, corolla, androecium, and gynoecium. These are attached to the swollen terminal of the pedicel called the thalamus.

Symmetry

• Actinomorphic: Radially symmetrical. Examples include chili, datura, and mustard.
• Zygomorphic: Flower can be divided into two equal parts in only one vertical plane. Examples include Cassia and pea.

Flowers can be trimerous, tetramerous, or pentamerous depending on the multiple floral appendages present 3, 4, or 5.

Depending on the presence or absence of bracts (reduced leaf present at the pedicel base), flowers are classified into Bracteate or Ebracteate.

Parts of a Flower

• Calyx: A flower’s outermost whorl is made up of leaf-like structures called sepals
• Gamosepalous: Sepals united
• Polysepalous: Sepals free
• Corolla: Made up of bright colored petals and present after sepals
• Gamopetalous: Petals united
• Polypetalous:  Petals free

Aestivation

Arrangement of sepals and petals.

• Valvate: sepals or petals touch each other and don’t overlap in a whorl. Example: Calotropis
• Twisted: sepal or petal overlaps the next sepal or petal, and the same continues in a whorl. Examples include cotton, China rose, and lady’s finger.
• Imbricate: margins of sepal and petals overlap each other randomly and not in one direction. Examples include Gulmohar and Cassia.
• Vexillary: the largest petal overlaps two petals (wings) present laterally on both sides, and that overlaps the two anterior petals (keel) in the same way, also called papilionaceous. Examples include beans and peas.

Placentation

A specific arrangement of ovules in the ovary.

• Marginal: Pea
• Axile: Lemon and china rose
• Parietal: Argemone and mustard
• Free central: Primrose and Dianthus
• Basal: Marigold and sunflower

Also See: Morphology of Roots and its Types

Functions

• Reproduction
• Production of diaspores without fertilization
• Development of gametophytes
• Attracts insects and birds for transfer of pollen from the anther of one flower to the stigma of another
• The ovary develops into fruit that contains the seed

Fruit

Fruits are developed from a ripe ovary that contains seeds. They are a rich source of vitamins, minerals, and fibers. 

Parts

• Pericarp: Wall of the ovary that forms the wall of fruits. It can be fleshy or dry. It is further divided into three layers:
• Epicarp: Outermost layer that forms the peel
• Mesocarp: Middle layer, fleshy, edible portion of the fruits
• Endocarp: Innermost layer, the rough inner portion where the seed is accommodated

Seed

 Ovule develops into a seed after fertilization and has a seed coat and an embryo. The embryo comprises a radicle, embryonal axis, and one or two cotyledons in monocotyledons (maize, wheat) and dicotyledons (pea, gram).

Frequently Asked Questions on Morphology of Plants