Major defensive structures of plants include thorns, spines and prickles. Did you know they’re different? Thorns, officially, grow from the stem or shoot of the plant. They’re like miniature, pointy branches. Hawthorns and lemon trees, for example, have thorns. Spines grow from leaf tissues. Some leaves develop spinous points; some leaves fully convert into spines (like on cacti). Prickles grow from the plant’s outer surface of cells (the epidermis). Since the epidermis is found all over a plant, prickles can pop out of anywhere. “Thorns” on roses are actually prickles. And the spikes growing all over the leaves of this horsenettle (Solanum carolinense) are… prickles.
But these defensive structures may be more prickly (or thorny?) than we ever imagined. Preliminary research indicates that harmful (even deadly) microorganisms inhabit thorns, spines or prickles and cause further injury to herbivores who dare to challenge the awesome power of plants (1).
- Halpern M, Raats D, Lev-Yadun S. The Potential Anti-Herbivory Role of Microorganisms on Plant Thorns. Plant Signaling & Behavior. 2007;2(6):503-504.