An Overview of Plant Diversity

Introduction to Plants

Plants are a highly significant kingdom of organisms. They are multicellular organisms with the incredible capability to produce their food from atmospheric carbon dioxide. If plants were absent, animal life would not survive because they serve as the base of many food webs.

Like the vast Californian sequoias, plants can be as large as 90 metres, or as small as a few millimetres. While Eucalyptus regnans is the tallest angiosperm, Wolffia is the smallest rootless aquatic plant. The most common types of plants on earth are angiosperms or blooming plants. This overview looks at plant diversity based on habitat, stem nature, life span, size and nutrition.

Table of Contents

• Introduction to Plant Diversity
• Diversity Based on Habitat
• Diversity Based on Habit
• Angiosperm Diversity Based on Stem Nature
• Diversity Based on Size
• Diversity Based on Life Span
• Diversity Based on Nutrition
• Frequently Asked Questions (FAQs)

Introduction to Plant Diversity

Kingdom Plantae emerged about 410 million years ago as green algae transitioned from water to land. This land had a rich resource base and was comparatively uncolonised. Additionally, terrestrial habitats provide more light and carbon dioxide, essential for plant growth and survival.

Being multicellular and mostly photosynthetic organisms living both in water and on land, plants can be found almost everywhere. Red, brown, and green algae are among the aquatic plants, and mosses, ferns, gymnosperms, and angiosperms are among the terrestrial plants. Over the past 70 million years, flowering plants known as angiosperms have dominated the planet.

Diversity Based on Habitat

Depending on different characteristics, there are various types of plants. Plants are divided into the following groups according to their habitat (where they reside).

Hydrophytes

The term “hydrophytes” refers to plants that grow in or near water. Such plants have weak vascular tissue, fragile stems, and poor root systems. The majority of the tissue has air spaces and is spongy.

These plants might include the following characteristics:

(i) Submerged (e.g., Hydrilla, Vallisneria, Potamogeton etc.)

(ii) Fixed-floating and free-floating (e.g., Utricularia, Wolffia, Salvinia, Lemna, Ceratophyllum, Pistia, Trapa, Eichornia, etc.)

(iii) Amphibious (partly submerged, e.g., Alisma plantago, Ranunculus aquatilis, Sagittaria, etc.)

Thalassia and Zostera are two angiosperms that are also marine.

Hygrophytes

These plants need moist, dark environments to develop. Their roots and stems have limited growth and are fragile and spongy. The leaves have stomata and are fully developed. Ferns, Aroids, Begonias, and certain grasses are common examples.

Halophytes

These plants can survive in saline water or soil. They can tolerate high salt concentrations (NaCl, MgCl₂, and MgSO₄). They have distinctive breathing roots, or pneumatophores, that are negatively geotropic. Mangrove vegetation like Rhizophora, Ceriops, Avicennia, etc. are common examples.

Mesophytes

Mesophytes, which comprise the majority of angiosperms, are those that grow in areas with moderate water availability. They usually develop fast and are large. Their leaves and roots are well developed. The stem could be either woody or herbaceous. Some mesophytes, like deciduous trees, are mesophytic in the summer and xerophytic in the winter.

Xerophytes

Xerophytes, such as Acacia, Euphorbia, Amaranthus, Argemone, Nerium, and Ziziphus, are plants that thrive in xeric or dry environments or areas with limited access to water. Some xerophytes are known as succulents because they store water in their stems (Opuntia), leaves (Bryophyllum, Agave), or roots (Asparagus).

Epiphytes

Epiphytes are plants that grow on trunks or branches of other plants, such as an orchid or lichen growing as an epiphyte on a mango limb. The epiphytes are regarded as space parasites. An example of commensalism where the host is unaffected is the contact between an orchid (a commensal) and a tree (the host).

Parasitic Plants

These plants, such as Striga and Cuscuta, are parasites that grow on other plants (on roots of jowar).

Diversity Based on Habit

Angiosperms are divided into four groups based on their form, size, and shape:

Herbs (Herbaceous)

These plants have a short, green, fragile stem. Typically, they have a brief life span, like wheat or gram. Some herbaceous plants have a much reduced underground stem portion, but the aerial branch with flowers at the apex develops from the underground part during reproduction. Such a stem is known as a scape, such as an onion.

Shrubs (Shruby or Fruticose)

These plants are more significantly woody and branching than herbs. They generally have multiple stems but no main axis. Eg., henna, roses, and China roses.

Trees (Arborescent)

The plants are thick, rigid, and woody and are more prolonged or taller than bushes. They have a noticeable trunk.

Culms

Nodes and internodes are very apparent in these plants. Most of these plants have hollow internodes. These plants, such as bamboo, are grasses but cannot be classified as herbs, shrubs, or trees.

Angiosperm Diversity Based on Stem Nature

The angiosperm plants can be categorised as follows based on the type of stem:

Erect

These plants develop upright. Due to their strong stems, most trees, shrubs, and some herbs can stand upright on the ground.

Creepers

These plants have dangling stems that are entirely covered in roots. Leaves originate from nodes, from the culm of which branches emerge. For example, Cynodon, and Oxalis (doob grass). Nodes along the length of the stem produce adventitious roots.

Trailers

These plants resemble creepers, but adventitious roots do not form at nodes in these plants. A trailer could be procumbent or decumbent. The stem is horizontal in a procumbent trailer (such as Basella), but in a decumbent trailer, the apex of the stem is lifted above the ground (e.g., Lindenbergia).

Climbers

These weak-stemmed plants, such as peas and betels, cling to supports using their adventitious roots, petioles, spines, and tendrils.

Diversity Based on Size

The size of the angiospermic plants varies considerably. The rootless aquatic Wolffia is the smallest angiosperm. Its diameter is 0.1 mm. The diameter of aquatic Lemna is 0.1 cm. The Eucalyptus regnans tree is the tallest angiosperm plant. Its height exceeds 100 metres. Some eucalyptus trees grow as tall as 130 metres. The Banyan tree is the largest type of plant (Ficus bengalensis). It has more than 200 prop roots and can cover a space of 2 to 5 acres.

Diversity Based on Life Span

Angiosperms are divided into the following four groups based on life span:

Ephemerals

Before the arrival of real dry conditions, these plants reach the end of their life span in a very short time. These plants, such as Solanum xanthocarpum, Argemon mexicana, Cassia tora, etc., are not true xerophytes and are often referred to as drought escapers or drought evaders.

Annuals

After producing seeds, such as those for rice, wheat, and gram, they die within a year of completing their life cycle.

Biannuals (or Biennials)

These plants go through their entire life cycle in two years. They only exhibit vegetative development in the first year, and then, in the second year, they produce flowers, fruits, and seeds. Usually, these plants are herbs, such as carrot, turnip, and radish.

Perennials

Once established, these plants continue to live for a very long time. More than 200 years old, the giant banyan tree (Ficus bengalensis) can be found in Kolkata’s Botanical Garden. At Gaya, there is a Bodhi tree (Ficus religiosa) that is roughly 2500 years old.

Most perennials produce flowers and fruits in a specific season of the year after reaching maturity. They are polycarpic, including Acacia, mango, and coconut. Some perennial plants, like bamboo and Agave, are monocarpic, meaning they only produce fruit once during their lifetime. Biennials and annuals are all monocarpic.

Diversity Based on Nutrition

Plants are divided into the following categories based on their mode of nutrition:

Autotrophs/ Autophytes

They have the ability to produce their food. They are split into two groups: chemotrophs, which produce their food using chemical energy, and phototrophs (which produce their food through photosynthesis).

Heterotrophs

These plants cannot produce their food and therefore depend on external sources. Heterotrophs can be insectivorous, saprophytic, parasitic, or symbiotic.

Other plant varieties include:

• Polygamous plant (e.g., mango).
• Stolon plant (e.g., Ajuga, Stachys, and Mentha).
• Seedless vascular plants
• Sucker plant (red raspberry, lilac, and Forsythia).
• Air layering plants (Forsythia, jasmine, Hamamelis, Philodendron, etc.).
• Cutting plants.

There are various types of plants, and each one needs a specific environment to develop. The essential elements are sunlight, nutrients, water, air, soil, and temperature, which plants rely on for their life, growth, and development.

Related Links:

• Biodiversity and its Types
• What is Species Diversity?
• Flora And Fauna
• Biodiversity in Plants and Animals
• Plant Kingdom – Members of Kingdom Plantae

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