How to Identify and Distinguish Thorns and Spines in Plants
It is difficult to spot the difference between thorns and spines based only on their appearance since they both look almost identical. To know what is the difference between thorns and spines, we must look at how these two are created from different parts of a plant. While the thorn is a modified stem, the spine is a modified leaf. At Vedantu, we have created a comprehensive summary of spines, thorns, and pickles along with their differences.
Spines
Spines are sharp, pointed structures on a plant and are modified leaves. They protect the plant from predators. An example of spines can be seen in the Opuntia plant where the minute leaves of axillary buds transform into spines. Another example is pineapple where the margin of leaves is modified into spines.
Thorns
Thorns are woody, pointed structures in a plant that protect the plant and help in climbing. They are modified axillary leaves and are different from both spines and prickles. Thorns may be branched or unbranched and are always subtended by a leaf.
What is the Difference between Thorns and Pickles?
Spines are structures that are sharp in nature and are pointed. They are part of the plant and are modified leaves. These provide protection of the plants from predators. An example of spines is observed in the Opuntia plant where the leaves or buds of the axillary transform into spines. Another example of such plants is pineapples which have the margin of their leaves modified into spines. Spines are thus modified leaves or stipules which are parts of the leaves and have extensions of the leaf veins. The spines have vascular tissues. They are also called petiolar spines or leaflet spines and even stipular spines which are examples of spines that develop as a leaf part that has midrib, petiole, and secondary veins. Spines are observed widely in the family of cactus. The cacti have a particular kind of spine that is of different origin and are called glochids. The glochids are small and deciduous with many retrorse barbs along the length of the plant. Thorns on the other hand are woody and pointed structures that protect the plant and also help them in climbing other surfaces. They are axillary leaves that are modified and they differ from prickles and spines. The thorns are either branched or not branched.
The terms prickles and thorns are often mixed and used interchangeably but there is a slight difference between thorns and prickles.
While thorns are formed from internal tissue (endogenous), prickles develop from external tissue ( exogenous).
Prickles develop from the epidermis and cortex of plant stems while thorns are modified branches.
Prickles can also occur on leaves and protrude from the main veins of the leaf unlike thorns
Prickles can also be seen on adventitious roots and some fruits unlike thorns
An example of prickles is the rose plant.
Spines, thorns, and prickles all prevent the animals from eating the plant.
Let’s look at the difference between thorns and spines in detail.
FAQs on Thorns vs Spines: What’s the Biological Difference?
1. What is the fundamental biological difference between thorns and spines?
The key difference lies in their developmental origin. A thorn is a modified, sharp-pointed stem or branch that arises from a bud, typically in the axil of a leaf. A spine, on the other hand, is a modified, sharp-pointed leaf or part of a leaf (like a stipule). This means thorns have an internal vascular system connected to the plant's stem, while spines are part of the leaf structure.
2. What are some common examples of plants with thorns and spines?
You can find clear examples of these modifications in different plants:
- Thorn examples: Plants like Citrus (lemon, orange) and Bougainvillea have true thorns, which are modified stems that arise from an axillary bud.
- Spine examples: The most famous example is the Cactus, where the spines are modified leaves that reduce water loss. Another example is the Barberry plant, which also has leaf spines.
3. How are prickles different from both thorns and spines?
Prickles are different from both thorns and spines because they are not modified stems or leaves. Instead, prickles are sharp outgrowths from the plant's outermost layers, the epidermis and cortex. A classic example is the rose. Because they are superficial, prickles can be easily snapped off the stem, unlike thorns which are deeply embedded and contain vascular tissue.
4. Why do plants develop sharp structures like thorns and spines?
Plants develop these structures primarily as a form of mechanical defence. Their main functions are:
- Protection from Herbivores: The sharp points deter animals from eating the plant, serving as a physical barrier.
- Reduction of Water Loss: In xerophytic plants like cacti, leaves modified into spines have a greatly reduced surface area, which significantly cuts down water loss through transpiration. Photosynthesis is carried out by the green stem.
5. Are thorns and spines considered homologous or analogous structures in biology?
Thorns and spines are classic examples of analogous structures. This means they perform a similar function (protection) but have different evolutionary and developmental origins (a thorn is a modified stem, a spine is a modified leaf). Homologous structures, in contrast, share a common origin but may have different functions, such as the forelimbs of humans and the wings of a bat.
6. How can you tell if a sharp point on a plant is a thorn or a spine?
You can often identify them by their position on the plant. A thorn typically grows from a leaf axil (the angle between the petiole and the stem), where a branch would normally develop. It may even bear its own leaves or flowers. A spine grows in the position of a leaf, and in plants like cacti, you'll find them emerging from distinct structures called areoles.
7. Does a cactus have thorns or spines?
A cactus has spines, not thorns. The sharp, needle-like structures covering a cactus are biologically classified as modified leaves. This modification is a crucial adaptation for survival in arid environments, as it helps conserve water by reducing transpiration and also protects the plant from being eaten by animals.
