Several plants have evolved various mechanisms both morphological and chemical to protect themselves against herbivory.
Morphological defence mechanisms:
- Cactus leaves (Opuntia) are modified into sharp spines (thorns) to deter herbivores from feeding on them.
- Sharp thorns along with leaves are present in Acacia to deter herbivores.
- In some plants, the margins of their leaves are spiny or have sharp edges that prevent herbivores from feeding on them.
Chemical defence mechanisms:
- All parts of Calotropis weeds contain toxic cardiac glycosides, which can prove to be fatal if ingested by herbivores.
- Chemical substances such as nicotine, caffeine, quinine, and opium are produced in plants as a part of self-defence.