The following points highlight the top sixteen types of defense mechanism in plants. The types are: 1. Thorns 2. Pointed spines 3. Prickles 4. Spines 5. Stinging hairs 6. Glandular hairs 7. Stiff hair 8. Latex 9. Alkaloids 10. Raphides 11. Smell and bitter taste 12. Tannin 13. Resin and essential oils 14. Geophilous habit 15. Myrmecophily 16. Mimicry.
Defense Mechanism: Type # 1. Thorns:
Many plants, such as lemon (Citrus), pomegranate (Punica), bael (Aegle marmelos), Duranta, and ber (Zizyphus) possess thorns to protect them from their enemies.
Defense Mechanism: Type # 2. Pointed spines:
The plants like pineapple, datepalm (Phoenix), Agave and Yucca have pointed spines at the leaf ends which protect them to some extent from enemies.
Defense Mechanism: Type # 3. Prickles:
The rose plants and silk cotton tree possess prickles which act as defence organs.
Defense Mechanism: Type # 4. Spines:
Opuntia and several other members of Cactaceae (cacti) have spines on their phylloclades which protect them from attack of animals.
Defense Mechanism: Type # 5. Stinging hairs:
The stinging hairs with sharp and siliceous apices occur on all parts of the body in nettles (Laportea), Urtica dioica and several other members of Urticaceae which protect the plants from their expected enemies.
Defense Mechanism: Type # 6. Glandular hairs:
Glandular hair with sticky substances is found on plant body of Jatropha, Boerhaavia and tobacco (Nicotiana) which protect them from outer agencies.
Defense Mechanism: Type # 7. Stiff hair:
The dense coating of such stiff hair is repulsive to attacking animals; they are found on cud weed (Gnaphalium) and many cucurbits.
Defense Mechanism: Type # 8. Latex:
Several species of plants, such as Nerium, Ficus and Euphorbia have latex in their different parts. The latex protect these plants to some extent from his enemies.
Defense Mechanism: Type # 9. Alkaloids:
Several plants, such as Poppy (Papaver), Datura and tobacco (Nicotiana) possess alkaloids in them which are poisonous and give protection to the plants.
Defense Mechanism: Type # 10. Raphides:
Calcium oxalate crystals are also known as raphides which are irritating and poisonous. They are found in Colocasia and several other members of Araceae (aroids). They help in defense of these plants.
Defense Mechanism: Type # 11. Smell and bitter taste:
Several plants of Lamiaceae, such as Ocimum and mint have typical smell and bitter taste which protect the plants from attack of insects. Neem and Karela have also bitter taste.
Defense Mechanism: Type # 12. Tannin:
Several plants such as Acacia nitotica. Acacia catechu, etc., possess tannins in them which act as substances of protection.
Defense Mechanism: Type # 13. Resin and essential oils:
In many angiosperms resins and essential oils are present. In Pistacea and other members of Anacardiaceae the gums and resins are found which protect them from several injurious agencies.
Defense Mechanism: Type # 14. Geophilous habit:
Zinger (Zingiber officinale), turmeric (Curcuma longa), colocasia and onion are main representatives of this habit. This underground habit protects them from several injurious agencies.
Defense Mechanism: Type # 15. Myrmecophily:
Some plants, such as guava (Psidium spp.), mango (Mangifera indica) have a habit of harbouring ants which save the plants from the damage by other organisms.
Defense Mechanism: Type # 16. Mimicry:
This is habit of initiating the general appearance, colour and shape of other plants, generally disliked by attackers. For example, the aroids (Cladium) and Sansevieria resemble spotted snakes and thus by this habit keep away from plant-eating animals. The species of Arisaema (aroid) possess hood like inflorescence which resembles cobra in appearance and thus protect them from invading animals.