As a means of protecting themselves, several trees produce thorns to discourage herbivores from eating the foliage. One such tree is the Acacia Tree, which produces thorns (below, left) in a variety of sizes and shapes. These thorns fall off the tree with age or disturbance and float to various shorelines.

Another tree that produces such armor is the Kapok Tree (aka Silk-Cotton Tree, Ceiba pentandra). These "thorny" protuberances (below, right) cover the trunks and branches of trees until the tree becomes quite mature and they fall off. Although many people refer to these sharp protuberances as thorns or spines, technically (botanically, for this tree), they are called "Prickles"