Thorny plants are species that have sharp, pointed structures called thorns, which serve as a defense mechanism against herbivores. These thorns can be found on various types of plants, including roses, cacti, and blackberries. They help protect the plant from being eaten and can also reduce water loss by minimizing damage from animals. Thorns can vary in size and shape, ranging from small prickles to large, formidable spikes. Some plants, like acacia trees, have evolved to develop thorns that are hollow and can house ants, creating a mutualistic relationship where the ants protect the plant from herbivores in exchange for shelter.