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Spine (botany)

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Spine (botany)

In plant morphology, thorns, spines, prickles, and in general spinose structures (as spinose teeth, spinose apical process) are all hard structures with sharp, stiff, ends, all of them with the same function of mechanically deterring herbivory. In common language the terms are used more or less interchangeably, but in botanical terms, thorns are derived from shoots (so they can be branched or not, they can have leaves or not, and they arise from a bud),[1][2][3][4] spines are derived from leaves (the entire leaf or some part of the leaf that has vascular bundles inside, like the petiole or a stipule),[1][2][3][4] and prickles are derived from the epidermis (so they can be found anywhere on the plant, and don't have vascular bundles inside so they can be removed more easily and cleanly than thorns and spines[4]).[1][2][3] Leaf margins also may have teeth and if those teeth are sharp they are called spinose teeth, on a spinose leaf margin[1][2] (some authors consider them a kind of spine[2]). On a leaf apex, if there is an apical process (generally an extension of the midvein), and if it is specially sharp, stiff, and spinelike, it can be called spinose or pungent apical process[1] (again, some authors call them a kind of spine[2]) When epidermis is covered with very long, stiff trichomes (more correctly called bristles in this case,[1] for some authors a kind of prickle[2]) is called hispid vestiture,[1][2][3] if is covered with stinging trichomes it can be called urent vestiture.[1]

Thorn images.

Types of spines. Cacti can have a particular kind of spine (modified leaf) very small and deciduous, with numerous retrorse barbs along its length, this particular spine is called glochidium (plural glochidia or glochids), as found in areoles of Opuntia.[1] Spines can be petiolar spines as those of Foquieria, leaflet spines as in Phoenix, stipular spines as in Euphorbia, all those are examples of spines developing from a part of a leaf containing the petiole, midrib, or a secondary vein.[1]

Spine images.

Prickle images.

Spinose teeth, spinose apical process, stiff trichome, stinging trichome.


The predominant function of thorns, spines and prickles is deterring herbivory in a mechanical form.

Not all functions of spines or glochids are limited to defence from physical attacks by herbivores and other animals. In some cases, spines have been shown to shade or insulate the plants that grow them, for example, the saguaro cactus spines shade the apical meristem in summer and in members of the Opuntioideae glochids insulating the apical meristem in winter.

Agrawal et al. (2000) found that spines seem to have little effect on pollinators, which the plants need in order to reproduce.[5]

Definitions and technical distinctions

  • Thorns are modified branches or stems. They may be simple or branched.
  • Spines are modified leaves, stipules, or parts of leaves, such as extensions of leaf veins.
  • Prickles are comparable to hairs but can be quite coarse (for example, rose prickles), i.e. they are extensions of the cortex and epidermis.[6][7]

Spinescent is a term describing plants that bear any sharp structures that deters herbivory. It also can refer to the state of tending to be or become spiny in some sense or degree, as in: "...the division of the African acacias on the basis of spinescent stipules versus non-spinescent stipules..."[8]

Some authors prefer not to distinguish spines from thorns because, like thorns, and unlike prickles, they commonly contain vascular tissue.[9]

Technically speaking, many plants commonly thought of as having thorns or spines actually have prickles. Roses, for instance, have prickles.[9]


It has been proposed that thorny structures may first have evolved as a defense mechanism in plants growing in sandy environments that provided inadequate resources for fast regeneration of damage.[10][11] However, the suggestion was unsupported by any argument to discount the likelihood that spiny defences might have been developed as a means of defence in resource-rich environments where herbivory might have been more intense than in the hypothesized sandy environments.

Morphological variation

Spinose structures occur in a wide variety of ecologies, and their morphology also varies greatly. They occur as sharpened branches (e.g. in Carissa, Citrus, Crataegus), spiky inflorescences (e.g. in Tylecodon reticulatus),[12] a tiny point at the tip of the leaf (mucronate leaves) (e.g. in Sansevieria),[13] leaves fully converted to spines (e.g. in Opuntia),[14] stipules converted to spines (e.g. in many Acacia), prickles on stems (e.g. of Rosa, Erythrina and Ceiba speciosa), uriticating (i.e. stinging) hairs, bristles, and finely barbed spines called glochids. Some thorns are hollow and act as myrmecodomatia, others (e.g. in Crataegus monogyna) bear leaves. Thorns of some species are branched (e.g. in Crataegus crus-galli, Carissa macrocarpa).

In human culture

Primitive humans are known to have used thorns as tools. Human history records a variety of cultural references to sharp-pointed plant defensive mechanisms. The Book of Genesis recounts the creation of thorns as one of the punishments for the sin of Adam and Eve, stating, "Thorns also and thistles shall [the ground] bring forth to thee; and thou shalt eat the herb of the field." Genesis, 3:18. One of the most enduring cultural images is the Crown of Thorns described in the Bible as having been placed on the head of Jesus before his crucifixion. It is mentioned in the Gospels of Matthew (27:29), Mark (15:17), and John (19:2, 5) and is often alluded to by the early Christian Fathers, such as Clement of Alexandria, Origen, and others. For example, John the Evangelist states that "the soldiers plaited a crown of thorns, and put it on his head". (KJV, ch. 19). The biblical account does not specify what kind of thorns were involved, and leaves no clues from which to determine whether these were biologically classifiable as thorns, spines, or prickles. In modern times, the oxygen isotope composition of spines from saguaro cactus have been shown to record changes in local rainfall and can be used to reconstruct climate and plant ecophysiology over the plant's lifetime Acanthochronology.

An early popular myth involving a thorn is that of Androcles, a fugitive slave in ancient Greece who was said to have befriended a lion by pulling a thorn from the lion's paw.[15]

The status of the Scottish Thistle as the national emblem of Scotland is founded on the story (recounted here) that an invading Norse army attempting a night attack was betrayed when they encountered a thistle in the dark.

Plants bearing thorns, spines, or prickles are often used as a defense against burglary, being strategically planted below windows or around the entire perimeter of a property.[16]

They also have been used to protect crops and livestock against marauding animals. Examples include hawthorn hedges in Europe, Agaves in the Americas and in other countries where they have been introduced, Osage Orange in the prairie states of the US, and Sansevieria in Africa.[17]

See also


General references:

  • Simpson, M. G. 2010. "Plant Morphology". In: Plant Systematics, 2nd. edition. Elsevier Academic Press. Chapter 9.
  • Judd, Campbell, Kellogg, Stevens, Donoghue. 2007. "Structural and Biochemical Characters". In: Plant Systematics, a phylogenetic approach, third edition. Chapter 4.
  • Esau, K. 1965. Plant Anatomy, 2nd Edition. John Wiley & Sons. 767 pp.
  • Llamas, K. A. 2003. Tropical Flowering Plants. Timber Press, Portland. 423 pp.

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