Introduction to Plant Morphology: Definition, Significance, Diagrams

Introduction to Plant Morphology: Have you ever wondered why the leaves of pine, oak, and cabbage all look very different but share certain basic structures and arrangements of parts? Plant morphology is the study of a plant’s structure, development, and form. Plant morphology is extremely important for visually identifying plants.

The study of morphology is important to know about the economic importance of any plant. Plant morphology provides the foundation for understanding function, taxonomy, heredity, ecology, development, and other aspects of biology and serves as a platform for further research. Let us scroll down to know more about Introduction to Plant Morphology in detail.

What is Plant Morphology?

Plant morphology is the science that studies the exterior structures, forms, sizes, colour, form, and development of plants. Morphology is derived from the Greek words ‘Morphe’ and ‘Logos,’ which mean ‘Form’ and ‘Study,’ respectively. Phyto morphology is another name for plant morphology.

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Importance of Morphology

The importance of Morphology are as follows:

1. Morphology is the basis or building block for a variety of topics to study, allowing us to explore numerous aspects of biology and obtain a better understanding of the different topics.
2. Morphology can study the diverse influences of genetics, ecology, anatomy, etc.
3. Morphology explains the structure of different plants of the same species or other species and provides information about variations found in a species.
4. Plant morphology includes both the vegetative and reproductive structures of plants. Root and shoot systems are examples of vegetative structures. Flowers, seeds, and ferns are only a few reproductive structures.
5. Plant morphology describes the structure of plants throughout a wide variety of scales. The smallest scales are ultrastructure. The largest scale is plant growth.
6. Deficiency and toxicity symptoms are morphological changes that develop due to a mineral deficiency or excess.
7. Plant Morphology also describes the developmental pattern, or how a plant’s structure develops and increases.
8. In the fields of genetics and taxonomy, plant morphology research is used.
9. Horticulturists use plants with unique morphologies in lawns, gardens, and parks, among other places.

Angiosperm Diversity

Angiosperms are the most advanced, evolved, and abundant plant species. Flowering plants, also known as angiosperms, have dominated the globe for 70 million years. There are about 3,00,000 angiosperm species on the planet, each with a broad range in size, form, life span, habit, habitat, nutrition, and other characteristics. There are over 45,000 plant species recognised in India, accounting for about 7% of the world’s flora. India is home to around 4,900 species of angiosperms.

Diversity based on Size: Angiosperms are the world’s largest plant group. Angiosperms exist in a wide range of sizes and shapes, from tiny plants to towering forest trees. Flowers, carpels, stamens, and tiny pollen grains are found in all angiosperms. Its diameter ranges from 0.1 mm to 130.5 m. The smallest angiosperm tree is Wolffia, whereas the largest is Eucalyptus regnans. The largest giant Banyan tree can cover 2-5 acres in area.

Diversity based on Habit: The stem’s shape, size, form, and character define the habit. Angiosperms are usually divided into three groups based on habit:

1. Herbs: Herbs are seed-bearing, tiny, soft, delicate, non-woody plants that produce seeds. Herbs only live for a limited time. At the end of the growing season, they die. Herbal parts are valued for their medicinal and aromatic properties. Herbs have a single stem with no branches. The three types of herbs are biennials, perennials, and annual. Culinary herbs include perennials like lavender and thyme, biennials like parsley, and annuals like basil.

Fig: Herb

2. Shrubs: Shrubs are woody, medium-sized, branched, and bigger than herbs.  They don’t have a main trunk and usually branch at or around the base. Their height ranges from 1-4 meters. They are mostly evergreen. For example, China rose, rose, and henna.

Fig: Shrub

3. Plants: Plants that are longer or larger than shrubs, hard and woody, well-developed and thick, and grow to a significant height. They have a large trunk. The trunk can be branched or not. A tree’s lateral branches are found at a certain distance from the ground.

Fig: Tree

Based on stem plants are the following types:

(a) Caudex: The stem is unbranched and usually has a crown of leaves at the apex, such as in the Date-palm.

(b) Excurrent: The lowest half of the stem is thicker, tapering upwards. The acropetal arrangement of branches on the main stem gives the plant a conical appearance. Example: Pinus, Casuarina, etc.

(c) Deliquescent: After a period, the apical bud of the main stem dies, and branches and sub-branches disseminate in various directions. Example: Dalbergia, Ficus, etc.

(d) Culms: The nodes and internodes of these plants are particularly prominent, and the internodes are frequently hollow. These plants are grasses, but they are neither herb, shrubs, nor trees such as Bamboo.

There are additional types of plants in addition to these three groups.

4. Trailers: A trailer creeps along the soil’s surface without attaching itself. The plant with trailers has only one point of contact with the soil. Example: Tribulus, Euphorbia, etc.

Fig: Trailer

5. Creepers: Creepers are low-growing plants that grow close to the ground or against a wall or fence. They have fragile, long, thin stems that can’t stand straight or hold their entire weight. Watermelon, pumpkin, sweet potato, etc., are examples of creepers.

Fig: Creeper

6. Twiners: Twiners are climbing plants with touch-sensitive main shoots that wind themselves around supports like ropes and rods and grow upwards in this manner. Example: Ipomoea

Fig: Twiner

7. Climbers: Climbers are plants with long, slender, and very thin green stems that develop and carry their weight with the help of external support. Grapevine, beans, cucumber, etc.

Fig: Climber

8. Lianas: Lianas are a type of woody twiner or climber. Plants with a long, flexible climbing stem rooted in the ground and frequently have long dangling branches are known as vines, climbing plants, or climbers. Example: Hiptage, Pink honeysuckle, etc.

Fig: Lianas

9. Epiphytes: An epiphyte is a plant that grows on the surface of other plants rather than in the ground. Example: Vanda

Fig: Epiphyte

Diversity based on Lifespan: Angiosperms are divided into four categories based on their lifespan:

1. Ephemerals: Plants that live for only a few weeks are called ephemerals. This is because their growing season is quite short. These are not true xerophytes and are often referred to as drought evaders or drought escapers. The life cycle of Arabidopsis species is 20–28 days. Argemone mexicana, Solanum xanthocarpum, Cassia tora, Artemesia, etc.

Fig: Ephemeral Plant

2. Annuals: These plants can live and die in a single season if conditions are favourable. They grow in size and flower at this time. In the form of seeds, they survive an unfavourable period. Wheat, rice, maise, and other annual crops are examples.

Fig: Annual Plant

3. Biennials (also known as biannuals): These plants complete their life cycle in two seasons (i.e., in two years). They only show vegetative development the first year, then flowers, fruits, and seeds the second year. They frequently create storage organs, such as the sugar beet’s enlarged roots, which store food. After producing flowers and fruits, they die. Typically, these plants are herbs, such as radish, turnip, and carrot.

Fig: Biennial Plant

4. Perennials: Plants that live for more than two years are classified as perennials. They have a lengthy lifespan and can live for many years once established. The vegetative development of some of these perennials can last for several years. After reaching maturity, most perennials produce flowers and fruits in a specific season each year. Polycarpic plants include coconut, mango, Acacia, and others. Monocarpic perennials (such as bamboos and agave) yield fruit only once throughout their lives. Monocarpic plants are all annuals and biennials. The Botanical Garden in Kolkata has a 200-year-old huge banyan tree (Ficus bengalensis).

Fig: Perennial Plant

Diversity based on Habitat: The plant can grow in different types of habitats. Angiosperms are classified based on habitats into the following groups:

1. Hydrophytes: Hydrophytes are plants that grow near water or are submerged in it. These plants have poor root systems, soft stems, and vascular tissue. The majority of the tissue is spongy and has air spaces.

These plants could be:

(i) Floating (for example, Vallisneria, Hydrilla, Potamogeton, etc.)
(ii)-floating and fixed-floating (for example, Wolffia, Utricularia, Salvinia, Ceratophyllum, Lemna, Pistia, Eichornia, Trapa, Azolla, Nymphaea, etc.)
(iii) Amphibious (only partly submerged, e.g., Ranunculus aquatilis, Alisma plantago, Sagittaria, Limnophylla, etc.)

Zostera and Thalassia are two angiosperms found in the sea.

Fig: Hydrophytes

2. Mesophytes: Mesophytes are the majority of angiosperms that grow in areas with moderate moisture and temperature. They’re usually big and grow quickly. Their roots and leaves are highly developed. Herbaceous or woody stems are possible. Certain mesophytes, such as deciduous trees (those that shed their leaves at a specific time of year), are mesophytic in the summer and xerophytic in the winter. Example Sunflower, Artocarpus. 

Fig: Mesophytes

3. Xerophytes: Xerophytes are plants that grow in xeric or dry conditions or in areas where water is scarce. They face severe water scarcity. Therefore, to survive in such environments, they evolve morphological, structural, and physiological adaptations as a weapon. Euphorbia, Acacia, Argemone, Amaranthus, Calotropis, Nerium, Ziziphus, and others. Succulents are xerophytes that reserve water in their stems (Opuntia), leaves (Aloe, Agave, Bryophyllum), or roots (Asparagus). Some of them also store mucilage.

Xerophytes are further classified into the following groups:

i. Lithophytes – Plants that grow on the surface of rocks.

ii. Psammophytes – Plants that grow in sandy environments.

iii. Oxylophytes – Plants that flourish in acidic environments.

Fig: Xerophytes

4. Halophytes: These plants can be found in saline environments, i.e., salt marshes, alkaline soils, river estuaries, saline ponds near the seaside, and sandy and heavy soils.  They can withstand a relatively high salt content (NaCl, MgCl₂, and MgSO₄). They have pneumatophores, which are negatively geotropic breathing roots. Mangrove vegetations such as Rhizophora, Ceriops, Avicennia, Sonneratia, and others are common examples.

Fig: Halophytes

Diversity based on Nutrition: 

1. Autotrophic plants or autotrophs: In the autotrophic mode, organisms synthesise organic food on their own using simple inorganic raw materials like water and carbon dioxide in the presence of light and chlorophyll. This is accomplished through the process of photosynthesis. Autotrophic nutrition has been reported in plants, algae, and bacteria (cyanobacteria).

Fig: Autotrophic Plants

2. Heterotrophic plants or heterotrophs: Heterotrophs are organisms that are unable to prepare their nourishment. These plants rely on green plants or animals for food, or they get a portion or all their nutrition from outside sources. All non-green plants and animals, including humans, are classified as heterotrophs. Heterotrophs are again classified into:

i. Saprophytes: Saprophytes get their nutrition from decaying and dead things. Saprophytic nourishment is also used by some angiosperms. Neottia is a good example. As a saprophyte, the roots of Neottia (Bird’s Nest Orchid) interact with mycorrhizae and absorb nutrients. Monotropa (Indian Pipe) thrives in densely forested areas with humus-rich soil. Through mycorrhizal interaction, it receives nutrients.

ii. Parasites: Parasites are organisms that obtain their nutrients from another organism (host) and cause disease in that organism.

a. Obligate or Total, or Holo parasite – Produces haustoria and is dependent on the host for survival.

i. Total stem parasite: As a whole stem parasite, the leafless stem twines around the host, producing haustoria. Cuscuta (Dodder) is a rootless plant that can be seen growing on Zizyphus, Citrus, and other plants.

ii. Total root parasite: These parasites have no stem axis and develop in the roots of their hosts, producing haustoria. Rafflesia, Orobanche, and Balanophora are three examples.

b. Partial parasite or Hemiparasite- Plants in this group contain chlorophyll and manufacture carbohydrates. The amount of water and minerals required by the host plant varies.

i. Partial stem parasites: Loranthus and Viscum are two examples of partial stem parasites. 

ii. Partial root parasite: The Santalum album (Sandalwood tree) generates haustoria, which grows on the roots of a variety of plants when it is in its juvenile stage.

iii. Insectivores: Plants that grow in nitrogen-deficient environments develop an insectivorous behaviour to compensate for the lack of nitrogen. Drosera (Sundew), Utricularia (Bladderwort), and Nepenthes (Pitcher Plant), Dionaea (Venus flytrap), etc.

Fig: Heterotrophic Insectivorous Plants

Summary

Plant morphology is the science that studies the exterior structures, forms, sizes, colour, form, and development of plants. Morphology is derived from the Greek words ‘Morphe’ and ‘Logos,’ which mean ‘Form’ and ‘Study,’ respectively. Morphology provides the foundation for understanding function, taxonomy, heredity, ecology, development, and other aspects of biology and so serves as a platform for further research. Angiosperms are the world’s largest plant group. There are about 3,00,000 angiosperm species on the planet, each with a broad range in size, form, life span, habit, habitat, nutrition, and other characteristics.

FAQs on Introduction to Plant Morphology

Q.1. What is the morphology of a plant?
Ans: Plant morphology is the science that studies the exterior structures, forms, sizes, colour, form, and development of plants.

Q.2. Who is the “Father of Plant Morphology”?
Ans: Wilhelm Hofmeister, a German botanist, is commonly regarded as the “Father of Plant Morphology.”

Q.3. What are lithophytes?
Ans: Plants that grow on the surface of rocks are called lithophytes.

Q.4. Give one example of a total parasite.
Ans: Cuscuta (Dodder) is an example of a total stem parasite.

Q.5. Why is it important to know the morphology of plants?
Ans: 1. Plant recognition and identification require an understanding of morphology.
2. Morphology provides several significant criteria for classifying plants.
3. Morphology is needed to study various components of plant life, such as genetics, ecology, and anatomy.

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