While most people would bristle at the thought of being called prickly, a plant would consider it quite the compliment.
For us, prickliness has negative connotations. A prickly disposition means someone is easily irritated, a prickly sensation is one that is itchy and scratchy, and a prickly situation is one to avoid.
But for a plant, prickliness pays. It is a protective adaptation that allows the plant to survive while facing multiple challenges, the main one being herbivores hoping for a nice snack. In my garden, carnivores of the canine variety are the bigger problem; their rampages through the flower beds in pursuit of squirrels have felled less-protected plants. But even they now know not to tear through the rose garden.
In common parlance, the terms “prickles,” “thorns,” and “spines” are often used interchangeably, but botanically speaking, they are different things: prickles come from a plant’s epidermis (the outermost cell layer) and break off quite easily, thorns are modified plant stems, and spines are modified leaves or parts of leaves. Rose “thorns” are actually prickles.
In this post, I’ll focus on spines. Why? Because it still boggles my mind that spines are …. (modified) leaves.
Aside from being a source of protection, spines serve an important function for xeric plants (xerophytes: plants that have adapted to survive in environments with little water; cacti, aloes, agaves and other succulents are xeric plants). In desert areas, most plants with large, thin, flat leaves wouldn’t last very long; they would lose too much water. So desert plants had to adapt, or die. One of their adaptations was the modification of leaves into spines. Compared to traditional leaves, spines have a very small surface area, which reduces water loss. They reflect sunlight, deflect drying winds, and provide shade to the plant. At night, when it’s cooler, spines collect and drip condensed water vapor.
Knowing all this has expanded my thinking about “prickliness;” in this case, the pricklier the situation, the better!