Introduction to Biodiversity with Examples

Biodiversity is the variety of life on earth including all different plants, animals, and microorganisms; the genes they contain; and the ecosystem they form on land and in water. Biological diversity is constantly changing. It is increased by new genetic variation and reduced by extinction and habitat degradation. It has evolved the last 3.8 billion years on the earth. 

Biodiversity is the variety of life in all of its forms and at all levels of organization. It includes microorganisms such as bacteria-prokaryotes, unicellular or simple multicellular organisms such as protozoans, algae, and fungi, and most complex and multicellular organisms, like plants and animals. 

Plant Biodiversity:

The scientific study of plants is called botany. The term botany is derived from the Latin word Botane meaning pasture. Botany involves the study of plants in all aspects including morphology, anatomy, cytology, histology, taxonomy, physiology, genetics, phylogeny, and evolution.

A plant can be defined as:

Eukaryotic, multicellular,non-motile, spore-producing, chlorophyllous/pigmented, autotropic or photosynthesis organisms develop from having cellulosic cell wall. 

Plants can be classified based on two types:

• Vascular Tissue
• Seed Formation

1. On the basis of vascular tissues (xylem, phloem):

a. Atrachaeophytes: 

All the non-vascular plants (plants lacking xylem and phloem) in which there is poor body differentiation are grouped as Atrachaeophytes such as bryophytes. 

b. Trachaeophytes:

 All the vascular plants (plants in which xylem and phloem are present) are grouped under Trachaeophytes including Pteridophytes, Gymnosperms, and Angiosperms. 

Thallophyta: 

This term is generally used for organisms in which the body is thalloid like algae and fungi. Bryophytes are sometimes also placed in this group due to the thalloid body (being non-vascular).

2. On the basis of seed formation:

i. Cryptogams: 

All the seedless plants (plants not producing seeds) are grouped in cryptogams. These include Bryophytes and Pteridophytes.

ii. Phanerogams:

 All the seed-producing plants are placed in phanerogams also known as spermatophytes. Seed plants are Gymnosperms and Angiosperms.

Hence, there are four major groups of plants;

I. Bryophytes 

II. Pteridophytes

III. Gymnosperms

IV. Angiosperms

1. Bryophytes: Non-vascular, homosporous, gametophytic, seedless, non-flowering, non-fruiting plants in which gametophyte is the dominant generation while sporophyte is attached to it and partly or completely dependent on it for nutrition. The division Bryophyta has three classes;

> Hepaticopsida that includes Liverworts such as Riccia and Marchantia.

> Anthoceropsida that includes Hornworts such as Anthoceros.

> Bryopsida includes Mosses such as Funaria and Polytrichum.

2. Pteridophytes: Vascular, mostly homosporous or a few are heterosporous, sporophytic, seedless, non-flowering, non-fruiting plants in which sporophyte is the dominant generation. They are grouped with non-vascular seedless plants (bryophytes) because they are also seedless (cryptogams) and also with vascular plants (gymnosperms and angiosperms) as they have vascular system. So, they are also known as vascular cryptogams. The division Pteridophyta (excluding early vascular plants-Rhyniophytes) has four classes such as

> Psilopsida that includes Psilophytes such as Psilotum and Tmesipteris. > Lycopsida that includes Lycopods such as Lycopodium and Selaginella. > Sphenopsida that includes Horsetail such as Equisetum.

> Pteropsida that includes Ferns such as Adiantum and Marsilea.

3. Gymnosperms: Vascular, heterosporous, sporophytic, seeded, non-flowering, non-fruiting plants in which sporophyte is dominant generation. K.R. Sporne (1965) classified the gymnosperms into three classes which further divided into number of orders.

> Cycadopsida that includes Cycads such as Cycas and Zamia.

> Coniferopsida that includes Conifers such as Pinus, Abies, Taxus, Picea, Cedrus.

> Gnetopsida that includes Gnetales such as Gnetum, Ephedra and Welwitschia

4. Angiosperms: Vascular, heterosporous, sporophytic, seeded, flowering and fruiting plants in which sporophyte is dominant generation and gametophyte is highly reduced and dependent on sporophyte for nutrition. Examples: Solanum, Rosa, Hibiscus, Petunia, Tulipa. Evolution of plants: According to a hypothesis, the evolution of plants had already started 475 million years ago. The ancestor was actually a freshwater green alga called charophyte, which at first evolved to non-vascular plants (liverworts, hornworts and mosses) and then seedless vascular plants (ferns). It was not until 360 million years ago that seed plants, including non-flowering plants (gymnosperms) and flowering plants (angiosperms), emerged on Earth .