Characteristics and functions of plant spines

Just mentioning the word «thorns» immediately comes to mind a very peculiar type of plant: the cactus. Living in areas where temperatures can reach and even exceed 50 degrees Celsius, and where the rains are seasonal, the best way to save water they have found is not to produce leaves; or at least, not common leaves.

The truth is that there are different types of thorns, and each of them have their functions. So if you want to know everything about this incredible protection system (among other things) that some plants have, don’t take your eyes off the monitor .

What are thorns in botany?

The spines (in botany) are formations with a sharp tip that can be branched and that, as they have vascular tissue, their content in support tissue is very high. This also makes them rigid, unlike other similar structures such as stingers, which do not have vascular tissue.

Why do some plants have them? Well, let’s imagine for a moment that we are a plant and we live in an arid region, be it desert, steppe, dry forest or a thorn forest. In those places the insolation is not only high, but apart from that we would have to overcome another problem, if possible, greater: the shortage of water. It can rain a lot for several days or weeks a year, but drought complicates our lives most months.

In our favor we have a very strong survival instinct, typical of all living beings. But the production and maintenance of leaves involves a rather large water expense, an expense that we cannot afford. What do we do?

Explaining it in a simplified way, over the years (hundreds, thousands or perhaps millions of years), and as long as the conditions of the region remain more or less the same, we will stop producing common leaves and transform them into thorns, which do not require so much water and which, in addition, can be used for other very important things that we will see below.

What types are there?

There are several types of thorns, depending on their origin:

  • Caulinar spines: are those that originate from the transformation of the stems, and can also be called reduced branches. For example, Prunus spinosa or Gleditsia triacanthos possess them.
  • Leaf spines: they are those that originated from the transformation of the leaves, like all those plants of the Cactaceae (cactus) family, and those of the Berberis genus.
  • Radical thorns: they are the result of the modification of the root, which occurred through a lignification process. They are very rare.

What is the function of plant spines?

The spines of the plants fulfill different functions, which are the following:

Reduce perspiration

As we have just mentioned, these structures require less water both in their production and in their maintenance. But in addition, they lack stomata, which are two occlusive cells that are found in the epidermis (skin) of plants and that delimit a pore between them through which the gases inside the plants and those outside are communicated.

Thus, the loss of the precious liquid is much less.

They protect them from predators

As we know, there are herbivorous animals, and others that like to eat plants from time to time. If we add to these ‘dangers’ the drought and extreme heat that can occur in certain places, it is crucial to protect yourself. And the best way to do it is by producing thorns.

Although they cannot always fulfill their function (for example, when the predator is a voracious snail), in general they are very useful to keep safe.

They serve a bit of an ‘umbrella’

The fact that a plant has its entire body covered by thorns is a way to protect itself against the sun. Of course, this protection will be greater or less depending on the characteristics of these thorns: if they are long and very numerous, without a doubt your body will not be as exposed to the star king as if you only have some and/ or if you have them very short.

Can collect water

Whether it rains or if all there is is dew, each drop of water that is deposited on the thorns is directed to the body of the plants, where it will be absorbed through the pores. With this system then, they can stay hydrated, even if they live in the desert.

How useful are thorns for humans?

Nowadays, plants with thorns have a purely… defensive use. They are very interesting to have for example as protection hedges; although there are some that are collected for the beauty of their defensive structures, such as cacti.

On the other hand, it is known that in the past, and still today, indigenous tribes use them as tools, often hunting.

5 plants with thorns for garden

To finish, if you want to have thorny plants in your garden, then we are going to recommend these five:

Asparagus falcatus

Image – Wikimedia/ Ewen Cameron

Known as sickle asparagus, Asparagus falcatus is a spiny, broad-leaved plant that could well be mistaken for a bamboo… although it is not at all. It is native to southern Africa, and is a climbing and evergreen shrub that reaches a height of 6 to 7 meters. Its flowers are white and perfumed.

It does not resist frost. Suitable for indoor cultivation.


The Berberis is a genus of thorny evergreen shrubs or deciduous depending on species native to Europe, Asia, Africa, North and South America to reach a height of about 1-4 meters. The flowers are simple or in clusters, yellow or orange, and the fruits are edible berries but difficult to collect due to the amount of thorns these plants have.

They resist cold and frost down to -12ºC.

Echinocactus grusonii

Known as mother-in-law’s seat, golden ball, golden barrel, or hedgehog cactus, the Echinocactus grusonii is a species of cactus armed with strong spines endemic to central Mexico. It has a globular and spherical body, which over time can reach more than 1 meter in height.

It resists weak frosts down to -2ºC.

Phoenix dactylifera

Known as date, common palm, phoenix, tamara, or palm/ palm, the Phoenix dactylifera is a species of palm native to southwestern Asia. It grows to a height of 30 meters, with a single or multicaule trunk (with several stems) each 20 to 50 cm in diameter. The leaves are pinnate and spiny, and its flowers are grouped in inflorescences that sprout from spathes (modified leaves that protect the flowers) of brown color. The fruits are dates, red-chestnut berries when ripe and edible.

It resists cold and frost down to -12ºC. In the Canary Islands it is considered an invasive plant, and its trade, possession and introduction to the environment are prohibited.

Prunus spinosa

Known as blackthorn, Prunus spinosa is a thorny, deciduous shrub native to Central and Southern Europe that reaches a height of 4 to 5 meters. Its crown is very dense and branched, and it blooms in spring producing white flowers. The fruit is the blackthorn, an oval drupe of blue, purple or blackish color appreciated for the elaboration of pacharán.

Resists up to -18ºC.

What did you think of this topic? Did you know that the thorns of plants could have so many functions?

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