Why are plants prickly?
As plants cannot get up and run away from predators, they have evolved alternative strategies
to avoid being eaten.
As well as producing unpleasant repellents and toxins, they bear thorns and spikes to make them less attractive to herbivores.
Prickles are not always just for defence, however. In the case of cacti, they help to trap and conserve water, which is useful in hot and dry environments.
What's the world's prickliest plant?
Defining the very prickliest of these resourceful plants is tricky, but there are a few contenders for prickliest plant in the world.
One might be the cactus with the longest prickles, Emory’s barrel cactus (Ferocactus emoryi), which can grow formidable spines up to 32cm long. Another cactus to avoid is the so-called jumping cholla (Cylindropuntia fulgida), whose stems detach and stick to anything unlucky enough to brush past it, and whose barbed, hooked spikes are difficult and painful to remove.
Cacti aside, one of the largest prickly plants in the world is the thorny acacia tree (above). This hardy tree has branches studded with menacing, needle-sharp spikes that hide among the leaves and ward off would-be snackers.
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Main picture: Ferocactus emoryi © Getty images