A modified leaf or part of a leaf forming a sharp pointed structure, often with a vascular trace leading to its base. If some or all of the leaves are modified into spines then leaf area, and hence transpiration, is reduced. Spines are thus common in xerophytes, such as cacti, their points sometimes acting as nuclei on which water droplets can condense, run down to the soil, and provide moisture for the plant. In such plants the functions of the leaf may be taken over by the stem (see cladode ). Spines also protect against herbivores and excessive sunlight. Compare thorn , prickle. |
