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The diversity of plant life is essential for supporting most of our terrestrial ecosystems.
Worldwide tens of thousands of species of higher plants, and several hundred lower plants are currently used by humans for a wide variety of purposes such as food, fuel, fiber, oil, herbs, spices, industrial crops and as forage and fodder for domesticated animals.
In the tropics alone it has been estimated that 25,000-30,000 species of plants have some edible parts (Heywood 1992) and up to 25,000 species have been used in traditional medicines.
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In addition, many thousands of species are grown as ornamentals in parks, public and private gardens, as street trees and for shade and shelter. Another important role of plant life is the provision of ecosystem services- the protection of watersheds, stabilization of slopes, improvement of soils, moderation of climate and the provision of a habitat for much of our wild fauna.
1. Food:
Humans and most other animals arc almost totally dependent on plants, directly or indirectly, as a source of energy Plants have the ability to convert the solar energy through photosynthesis. Food provides energy and raw materials which supports various life processes. Presently, three grass species – wheat, rice and maize supply 50% of world’s food.
The plant parts commonly taken as food are as follows –
i. Cereals- Rice (Oriza sativa), wheat (Triticum aestivum), maize (Zea mays), barley (Hordium vulgare), oat (Avena sativa), pearl millet or bajra (Pennisetum typhoidss).
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ii. Pulses- Pea (Pisum sativum), gram (Cicer arietinum), green gram (Vigna radiata), black gram (Vigna mungo), pigeon pea or arhar (Cajanus cajan), soyabean (Glycin max) etc.
iii. Vegetables- Potato, tomato, carrot, cabbage, cauliflowers, etc.
iv. Fruits- Apple, mango, grapes, guava, banana, melons, pomegranate etc.
v. Nuts-Almond, cash nuts, walnuts etc.
2. Edible Oils:
The edible oils are used for cooking, are obtained from mustard (Brassica compestris), coconut (Cocos nucifera), ground nut (Arachis hypogea), sunflower (Helianthus annuus) etc.
3. Beverages:
The common beverages obtained from plants are tea (Camellia sinensis), coffee (Coffea arabica) and cocoa (Theobroma cacao) etc.
4. Alcoholic Beverages:
These are obtained from anaerobic fermentation of sugars by yeasts. The three important sugar containing crops are grapes (Vitis vinefera) used in making wines and brandy; barley (Hordeum vulgare) whose germinating seeds used for making beer and whiskies and molasses of sugarcane (Saccharum officinarum) used in making rum.
5. Spices:
These are pungent or aromatic plant products which are used for flavoring food and making it more palatable and tasty. Species are derived from plant parts other than leaves.
Some of them are:
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i. Chillies – fruits of Capsicum frutescens.
ii. Coriander (Dhania) – fruits of Coriandrum sativum.
iii. Black pepper (Kali mirach) – dried fruits of Piper nigrum.
iv. Cinnamon (Dal-chini) – dried inner bark of Cinnamomum zeylanicum.
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v. Cardamons (Elaichi) – dried seeds Elettaria cardenomum.
vi. Cloves (Laung) – dried flower buds of Syzygium aromaticum.
vii. Cumin (Zeera) – fruits of Cuminum cyminum.
viii. Turmeric (Haldi) – rhizome of Curcuma domestica.
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ix. Saffron (Kesar) – dried stigmas and style-tops of the flower of Crocus sativus.
x. Thyme (Ajwain) – dried fruits of Thymus vulgaris.
xi. Nutmeg (Jaiphal) – kernel of dried fruit of Myristica fragrans.
xii. Vanilla – dried unripe-fruit of Vanilla plantifolia.
6. Timber:
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The important timber yielding plants are – sal (Shorea robusta), teak or sagon (Tectona grandis), sisso (Dalbergia sisso), oak (Quercus alba), sandal wood (Santalum album). Ceder (Cedrus deodara) etc.
7. Fibers:
Plant fibers are usually sclerenchyma cells, sometimes with collenchyma cells.
The important fiber yielding plants are:
i. Stem of flax (Linum sp.) – The flax fibers gives linen textile, water proof fabrics, paper used cigarette bound.
ii. Stem of Hemp (Cannabis sativa) – Hemp fibers are used for making ropes, carpets, cordage, bags and sacs.
iii. Leaf stalk of Manila hemp (Musa textiles) – The fibers are used for making cordage, marine cables, tissue paper, wrapping paper etc.
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iv. Sunnhemp (Crotolaria juncea) – The fibers are used for making canvas, ropes and fishing nets.
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v. Jute (Corchorus capsularis) – The fibers are used for gunny bags, ropes, carpets etc.
vi. Seed epidermis of Gossypium – Gives cotton.
vii. Seed epidermis of Ceiba pentandra – Gives kepok fibers used for stuffing mattresses and life jackets.
viii. Husk of Coconut (Cocus nucifera) – Gives coir
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Artificial fabricks like nylon derived from oil, itself derived from fossil plants.
8. Medicines:
Plant materials contain various compounds used as drugs and medicines.
The important medicinal plants are:
i. Foxglove (Digitalis purpurea) – contain glycosides (digitonin and digoxin) which are effective in treatment of heart failure.
ii. Opium poppy (Papauer somniferum) – contain opiates which are effective pain-relievers.
iii. Pacific yew (Taxus brevifolia) – contains anti-cancer agents called taxel.
iv. Periwinkle (Vinca rosea) – contain anti-cancer agents like vincabalastine and vincristine.
v. Cinchona sp. – contain quinine (an alkaloid) used as anti-malarial.
vi. Rauvolfia serpentine – contain alkaloids like reserpine, serpentine, rauvolfimine which are used to lower blood pressure, depress central nervous system and stimulate uterine contraction during child birth.
vii. Aconitum ferox – The root extracts contain alkaloids like aconite used in treatment of sore- threat, pain, diuretic, sedative and diaphoretic.
9. Other uses:
The most commercially valuable plant products are rubber (latex of Hevea sp.), resins, tennins, tobacco etc. The natives of Venezuela take the latex of Brosimum galactodendron (Cowtree) of family Moraceae as a substitute of milk.
