Several plants have evolved various mechanisms both morphological and

chemical to protect themselves against herbivory.

Morphological defence mechanisms:

$\to$ Cactus leaves (Opuntia) are modified into sharp spines (thorns) to deter

herbivores from feeding on them.

$\to$ Sharp thorns along with leaves are present in Acacia to deter herbivores.

$\to$ In some plants, the margins of their leaves are spiny or have sharp edges that

prevent herbivores from feeding on them.

Chemical defence mechanisms:

$\to$ All parts of Calotropis weeds contain toxic cardiac glycosides, which can

prove to be fatal if ingested by herbivores.

$\to$ Chemical substances such as nicotine, caffeine, quinine, and opium are

produced in plants as a part of self-defence.