How does a plant defend itself?

Plants are an important food source for a great number of species, but it’s hardly in a plant’s best interest to be under attack and eaten all the time.

Unlike prey animals, plants can’t run away from nibbling insects or large herbivores, so they’ve developed different defence mechanisms. Some of these defence mechanisms we are very familiar with. Prickles on rose bushes for example. Or the bark on a tree, which creates a hard barrier against hungry herbivores, also sharp spines like the ones on a cactus, can act as a deterrent, but there are so many other fascinating ways in which plants have developed ways to protect themselves.

Here are some of our favourite related facts:

• Physical barriers such as those plants with bark or thick waxy cuticles, are possible as inside the walls of a plant cell there is space for waxes and other fatty substances to be deposited to thicken and strengthen the plant. This process can be actively encouraged and boosted when a plant detects intruders.
• Other plants use another weapon: idioblasts (‘crazy cells’). These contain toxic chemicals or sharp crystals that will tear at animal or insect mouths as they try to chew on the plant. A well-known example of this are members of the Philodendron family, a common houseplant. If the leaves are chewed then the unfortunate human or pet doing so will experience burning sensations in the mouth and throat, swelling, choking and inability to speak, and vomiting.

• Stinging nettles have needle shaped cells that break and inject irritating toxins into herbivores or unsuspecting ankles on woodland walks.
• Fragrant plants produce plant chemicals that form components of essential oils, such as mint, cinnamon, rosemary, basil or sage. These may be delicious spices and seasonings for us, but their primary function is as an insecticide, or to protect against fungal or bacterial infection.
• Coffee seedlings produce high levels of caffeine, which are toxic to insects and fungi, but can also inhibit the germination of nearby growing plants. This gives the coffee plant an advantage against other plants which may compete for resources.
• Other plants form alliances with other species for protection. Some acacia tree species house stinging ant colonies inside their thorns and even generate food for its house guests. In return these aggressive ants defend their trees from all sorts of animals, plants and fungi. They will also remove the foliage of encroaching plants.

A very short summary on a fascinating and expansive topic.

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