Botanists use three different words for sharp things on plants. They are thorns, spines, and prickles. Thorns are the ends of branches that are hard and sharp. Spines are hard structures with sharp ends. There are many different kinds of spines, some on leaves, some grow instead of leaves. Prickles are on the outside of stems.
Spines, prickles, and thorns protect plants from plant-eating animals (defence against herbivory). Some plants and animals, such as the acacia tree and giraffe have evolved in response to each other. The plants grow very long spines and the animals develop very long tongues to reach past the spines and feed on the leaves.
Prickles on rose stems
Spines on this Acacia grow below the leaves (the stem is sideways in the picture)
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Thorns, spines and prickles Facts for Kids. Kiddle Encyclopedia.