A number of native tree species, such as Washington hawthorn ( Crataegus phaenopyrum), honey locust ( Gleditsia triacanthos), and black locust ( Robinia pseudoacacia), evolved with thorns. They grow from a plant’s stem tissue and contain internal vascular tissue (phloem and xylem).
Thorns occur in the axil of a leaf where a branch would normally develop, but instead, terminate in a sharp, hard, woody point. Each is an adaptation of a separate plant part. While the three terms are used interchangeably in casual conversation, botanically they are not the same. There’s a tendency to refer to any sharp pokey thing on a plant as a thorn, a spine, or a prickle. Basically, some of them serve as defense mechanisms to deter nibbling by herbivores, whereas others evolved as seed dispersal mechanisms. I’ll leave it up to the botanists and forensics experts to figure out how and when these structures evolved. But why? What purpose do they serve? Clearly, this called for a little sleuthing to find some answers.ĭelving into the subject, I learned that these outgrowths vary depending on which part of the plant they occur. Lots of plant species worldwide are armed with sharp, pointed outgrowths. My curiosity about the barbs on those seeds kicked into high gear as I contemplated their form and function.
