Plants are the renewable resources but plant diversity is not.

 Plant diversity refers to the existence of wide variety of plant species in their natural environments. There are around 300,000-500,000 species of vascular plants that exist on earth (Figure 1).

Land plants include bryophytes (mosses), lycophytes (ferns), gymnosperms (woody plants without flowers but seed and cones are present), and angiosperms (flowering plants).

Aquatic plants include varieties of algae. Diversity of plant life is important as it supports various life forms (decomposers and herbivores).

Introduction to Plants

Plants are multicellular and mostly photosynthetic organisms, which are found both in water and on land. They are the primary producers (autotrophs) and are of fundamental importance in a food chain.

Plants range in size from few millimeters in length to giant sequoias of California that reach 90 meters.

Wolffia is a smallest rootless aquatic angiosperm, whereas Eucalyptus regnans is the tallest

Figure 2. Wolffia globosa (Fresh water Alga)

Angiosperms or flowering plants are the dominant forms of plants on the earth.

Types of Plants

Plants may be categorized into several types depending upon various characteristics.

Based on their habitat (where they live), plants are classified into following groups (Figure 9):

Hydrophytes

Plants growing close to and submerged under water are called hydrophytes, e.g. Hydrilla (Figure 3), Wolffia, Sagittaria.

Figure 3. Hydrilla verticillata water weed

Hygrophytes

They grow in moist and shady habitats. Their leaves are well developed stem and roots are spongy, and show stunted growth, e.g. Ferns (Figure 4), Begonias.

Course HomeFigure 4. Fern

These plants grow in saline soil or water. Common examples are mangrove plants, e.g., Rhizophora (Figure 5).

Figure 5. Rhizophora (Mangrove trees)

Mesophytes

Plants that require moderate water for their growth and development are known as mesophytes. Majority of angiosperms belong to this group.

Xerophytes

The plants which grow in dry conditions or where water is negligible, are known as xerophytes, e.g., euphorbia, acacia (Figure 6), etc.

Figure 6. Acacia tree in the African savannah

Xerophytes store water in their stem (opuntia), leaves (aloe, bryophyllum), or in roots (asparagus). They are called as succulents.

Epiphytes

Plants that grow on the trunk or branches of the other plants, e.g., orchid (Figure 7), lichen.

Figure 7. Potted white orchids (Phalaenopsis)

Parasitic Plants

These plants live on other plants as parasites, e.g. Cuscuta (Figure 8).

Figure 8. Cuscuta

Figure 9. Types of plants on the basis of their habitat

Based on their nutrition, Plants are classified into two groups (Figure 10):

Autotrophs/ Autophytes

These plants can produce their own food. They are divided into phototrophs (produce their own food by photosynthesis) and chemotrophs (produce their own food by utilizing chemical energy).

Majority of plants belong to this group.

Heterotrophs

These plants are not able to produce their own food and depend on others for food. Parasitic and saprophytic plants belong to this group.

Figure 10. Types of plants on the basis of their nutrition

Based on their shape, size and form, angiosperms are classified into four groups:

Herbs

The stem of these plants is green, delicate and short. Their life cycle is short, e..g., wheat (Figure 11), gram.

Figure 11. Wheat

Shrubs

These plants are woody, branched, have several stems with no main axis, e.g. rose (Figure 12), hibiscus.

Figure 12. English rose garden

Trees

They are hard, woody, very well developed, and thick. Possess a trunk, e.g. banyan tree (Figure 13).

Figure 13. Banyan tree

Culms

In these plants, nodes and internodes are extremely prominent, e.g. bamboo (Figure 14).

Figure 14. Bamboo forest

Figure 4. Types of plants based on their habit

Based on the nature of stem, the angiosperms are classified into four groups:

Erect

These plants grow upright. Most trees (Figure , shrubs and some herbs belong to this group.

Creepers

These plants have trailing stem on which roots are present throughout. For example, Oxalis, Cynodon (doob grass). Adventitious roots arise from nodes throughout the length of the stem,

Trailers

They resemble creepers but lack the adventitious roots does not arise from nodes. Basella belongs to this group.

Climbers

Pea plants belong to this group. These plants have weak stem. They climb on some support by tendrils, spines, adventitious roots etc.

Figure 15. Types of plants based on their nature of stem

Based on their life-span, plants are classified into following four groups (Figure 16):

Ephemerals

These plants complete their life span within a very short period, eg. Solanum xanthocarpum.

Annuals

They complete their life-cycle within one year and die after producing seeds, e.g., wheat, rice

Biennials

These plants complete their life-cycle in two years. For first year, they grow by vegetative reproduction. In second year. they develop flowers, fruits and seeds, e.g., Radish.

Perennials

These plants have long life, e.g., banyan tree.

Figure 16. Types of plants based of their life span

What Plants need to survive and grow

Plants are found everywhere and have specific requirements to survive and grow. Sunlight, water, nutrients, air, soil, and temperature are the key factors. Plants rely upon for their survival, growth, and development.

Sunlight

Plants need sunlight to grow. Light is used as a source of energy for making food by the process called photosynthesis. The process of photosynthesis is unique to autotrophic (or green) plants.

Animals do not have the ability of photosynthesis and thus depend on plants and other animals for food. Hence, life on earth depends upon the sun.

Water and Mineral

Water is very important for every cell in our body. Plants also need minerals (nutrients) to survive. Both water and nutrients are taken up through the roots from the soil.

Most important nutrients are nitrogen (N), phosphorous (P), and potassium (K). However, other minerals like carbon, hydrogen, oxygen, potassium also constitute essential components for the survival of plants.

Fertilizers provides plants with nutrients; hence they are used by farmers to help grow all kinds of crops.

Air, Soil, and Temperature

Harmful pollutants make survival of plants difficult. Therefore, clean air is very important. Plants require oxygen to support cellular respiration (Figure 17).

Carbon dioxide is required for photosynthesis. Exchange of theses two gases with environment plays a crucial role in plant survival.

Healthy soil and appropriate temperature are also very important for their survival.

Figure 17. Role of sunlight, water, soil, and nutrients on life of a plant

• Threats to Biodiversity – Explained!

  
  

  Some of the main threats to biodiversity are: 1. Human Activities and Loss of Habitat, 2. Deforestation, 3. Desertification, 4. Marine Environment, 5. Increasing Wildlife Trade and 6. Climate Change.

  
  

  1. Human Activities and Loss of Habitat:

  Human activities are causing a loss of biological diversity among animals and plants globally estimated at 50 to 100 times the average rate of species loss in the absence of human activities. Two most popular species in rich biomes are tropical forests and coral reefs. 

  Tropical forests are under threat largely from conversion to other land-uses, while coral reefs are experiencing increasing levels of over exploitation and pollution. If current rate of loss of tropical forests continues for the next 30 years (about 1 percent per year), the projected number of species that the remaining forests could support would be reduced by 5 to 10 percent relative to the forest in the absence of human disturbance.

  

  
  
  

  The rate of decline would represent 1000 to 10,000 times the expected rate of extinction without deforestation by humans. Some studies suggest that, globally, as many as one half of all mammal and bird species may become extinct within 200 to 300 years. 

  Biodiversity loss can result from a number of activities, including: 

  (a) Habitat conversion and destruction; 

  (b) Over-exploitation of species

  

  
  
  

  c) Disconnected patches of original vegetation; and 

  (d) Air and water pollution. 

  Over the coming decades, human-inducted climate change increasingly become another major factor in reducing biological/biodiversity. These pressures on biodiversity are, to a large extent, driven by economic development and related demands including the increasing demand for biological resources. 

  

  
  that reduce biodiversity, jeopardize economic development and human health through losses of useful materials, genetic stocks, and the services of intact ecosystems. Material losses include food, wood, and medicines, as well as resources important for recreation and tourism. Losing genetic diversity, like losing species diversity, makes it even more likely that further environmental disturbance will result in serious reductions in goods and services that ecosystems can provide. 

  
  

  2. Deforestation:

  Forest ecosystems contain as much as 80 percent of the world’s terrestrial biodiversity and provide wood fiber and biomass energy as well as critical components of the global cycles of water, energy and nutrient. Forest ecosystems are being cleared and degraded in many parts of the world. 

  Current projections suggest that demand for wood will roughly double over the next 50 years, which will make increasing use of sustainable forest practices more difficult. In addition to threats to biodiversity and potential shortages in the supply of forest products, the degradation of forests represents an enormous potential source of green house gas emissions. 

  Forest ecosystems contain about three times the amount of carbon currently present in the atmosphere and about one-third of this carbon is stored above ground in trees and other vegetation and two-third is stored in the soil. 

  

  
  

  When forests are cleared or burned, much of this carbon is released into the atmosphere. According to current estimates, tropical deforestation and burning account for about one quarter of carbon emissions into the atmosphere from human activities. 

  3. Desertification:

  Desertification and deforestation are the main causes of biodiversity loss. Both processes are decisively influenced by the extension of agriculture. The direct cost of deforestation is reflected in the loss of valuable plants and animal species. Desertification process is the result of poor land management which can be aggravated by climatic variations. Converting wild lands to agriculture often involves ploughing the soils which leads in temperate regions to an average decline in soil organic matter between 25 and 40 per cent over twenty five years. 

  

  
  

  Decreasing soil organic matter is always a clear indication of soil degradation, and often is accompanied by reductions in water infiltration, fertility, and ability to retain fertilizers. Ploughing also exposes soils to wind and water erosion, resulting in large-scale pollution of freshwater resources. 

  4. Marine Environment:

  Oceans play a vital role in the global environment. Covering 70 per cent of the earth’s surface, they influence global climate, food production and economic activities. Despite these roles, coastal and marine environment are being rapidly degraded in many parts of the globe.

  

  
  

  

  
  
  

  In coastal areas, where human activities are concentrated, pollution, over-exploitation of resources, development of critical habitats such as wetlands, and mangroves, and water-flow from poor land-use practices have led to drastic reductions in near shore fisheries production and aquatic biodiversity. 

  
  

  5. Increasing Wildlife Trade:

  According to Nick Barnes, “Trade is another cause of biodiversity depletion that gives rise to conflict between North and South.” Global trade in wildlife is estimated to be over US $ 20 billion annually. Global trade includes at least 40,000 primates, ivory from at least 90,000 African elephants, 1 million orchids, 4 million live birds, 10 million reptile skins, 15 million furs and over 350 million tropical fish. 
  

  6. Climate Change:

  As climate warms, species will migrate towards higher latitudes and altitudes in both hemisphere. The increase in the amount of CO2 in the air affects the physiological functioning of plant and species composition. Moreover, aquatic ecosystems, particularly coral reefs, mangrove swamps, and coastal wetlands, are vulnerable to changes in climate. 

  

  
  

  In principle, coral reefs, the most biologically diverse marine systems, are potentially vulnerable to changes in both sea level and ocean temperature. While most coral systems should be able to grow at a sufficient pace to survive a 15 to 95 centimeter sea-level rise over the next century, a sustained increase of several degrees centigrade would threaten the long-term viability of many of these systems.