Thorns, spines, and prickles

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A plant with thorns Thorn mullu.jpg
A plant with thorns

In plant morphology, thorns, spines, and prickles, and in general spinose structures (sometimes called spinose teeth or spinose apical processes), are hard, rigid extensions or modifications of leaves, roots, stems or buds with sharp, stiff ends, and generally serve the same function: physically deterring animals from eating the plant material.

Contents

Description

In common language the terms are used more or less interchangeably, but in botanical terms, thorns are derived from shoots (so that they may or may not be branched, they may or may not have leaves, and they may or may not arise from a bud), [1] [2] [3] [4] spines are derived from leaves (either 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 epidermis tissue (so that they can be found anywhere on the plant and do not have vascular bundles inside [4] ). [1] [2] [3]

Leaf margins may also 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 especially sharp, stiff, and spine-like, it may be referred to as spinose or as a pungent apical process [1] (again, some authors call them a kind of spine [2] ). When the leaf epidermis is covered with very long, stiff trichomes (more correctly called bristles in this case; [1] for some authors a kind of prickle [2] ), it may be referred to as a hispid vestiture; [1] [2] [3] if the trichomes are stinging trichomes, it may be called a urent vestiture. [1]

There can be found also spines or spinose structures derived from roots. [5]

Function

The predominant function of thorns, spines, and prickles is deterring herbivory in a mechanical form. For this reason, they are classified as physical or mechanical defenses, as opposed to chemical defenses.

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

Agrawal et al. (2000) found that spines seem to have little effect on specialist pollinators, on which many plants rely in order to reproduce. [6]

Definitions and technical distinctions

Pointing or spinose processes can broadly be divided by the presence of vascular tissue: thorns and spines are derived from shoots and leaves respectively, and have vascular bundles inside, whereas prickles (like rose prickles) do not have vascular bundles inside, so that they can be removed more easily and cleanly than thorns and spines.

Thorns are modified stems and arise from buds Stem morphology type thorn.svg
Thorns are modified stems and arise from buds
Cactus areoles; shoot (yellow), spines (green) and glochids (also spines, green and little) Stem morphology type areole.svg
Cactus areoles; shoot (yellow), spines (green) and glochids (also spines, green and little)
(A) Thorn or spine
(B) Prickle Diferencia espina y aguijon.jpg
(A) Thorn or spine
(B) Prickle
A spinose tooth in a leaf margin Leaf morphology tooth spinose.png
A spinose tooth in a leaf margin
A spinose apical process Leaf morphology apical process spinose-pungent.png
A spinose apical process

Thorns

Thorns are modified branches or stems. They may be simple or branched.

Spines

Spines are modified leaves, stipules, or parts of leaves, such as extensions of leaf veins. Some authors prefer not to distinguish spines from thorns because, like thorns, and unlike prickles, they commonly contain vascular tissue. [7]

Spines are variously described as petiolar spines (as in Fouquieria ), leaflet spines (as in Phoenix ), or stipular spines (as in Euphorbia ), all of which are examples of spines developing from a part of a leaf containing the petiole, midrib, or a secondary vein. [1] The plants of the cactus family are particularly well known for their dense covering of spines. Some cacti have also glochids (or glochidia, singular glochidium) – a particular kind of spine of different origin, which are smaller and deciduous with numerous retrose barbs along its length (as found in areoles of Opuntia ). [1]

Prickles

Prickles are comparable to hairs but can be quite coarse (for example, rose prickles). They are extensions of the cortex and epidermis. [8] [9] Technically speaking, many plants commonly thought of as having thorns or spines actually have prickles. Roses, for instance, have prickles. [7]

Other structures

Other similar structures are spinose teeth, spinose apical processes, and trichomes. Trichomes, in particular, are distinct from thorns, spines, and prickles in that they are much smaller (often microscopic) outgrowths of epidermal tissue, and they are less rigid and more hair-like in appearance; they typically consist of just a few cells of the outermost layer of epidermis, whereas prickles may include cortex tissue. Trichomes are often effective defenses against small insect herbivores; thorns, spines, and prickles are usually only effective against larger herbivores like birds and mammals.

Spinescent is a term describing plants that bear any sharp structures that deter 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..." [10]

"Root spines" on the trunk of a Cryosophila species. Cryosophila warscewiczii, thorns of the Silver Star Palm. (11164016416).jpg
"Root spines" on the trunk of a Cryosophila species.

There are also spines derived from roots, like the ones on the trunk of the "Root Spine Palms" ( Cryosophila spp.). The trunk roots of Cryosophila guagara grow downwards to a length of 6–12 cm, then stop growing and transform into a spine. [5] The anatomy of crown roots on this species (roots among the bases of the living fronds) also alters during their life. [5] They initially grow upwards and then turn down and finally they, too, become spinous. [5] Lateral roots on these two types of roots, as well as those on the stilt roots on this species, also become spinous. [5] Some authors believe that some of these short spiny laterals have a ventilating function so they are 'pneumorhizae'. [5] Short spiny laterals that may have a ventilating function may also be found on roots of Iriartea exorrhiza . [5]

There are also spines that function as pneumorhizae on the palm Euterpe oleracea . [5] In Cryosophila nana (formerly Acanthorhiza aculeata) there are spine roots or root spines, some authors may prefer "root spines" if the length of the root is less than 10x the thickness, and "spine roots" if the length is more than 10x the thickness. [5] Adventitious spiny roots have also been described on the trunks of dicotyledonous trees from tropical Africa (e.g. Euphorbiaceae, as in Macaranga barteri , Bridelia micrantha and B. pubescens ; Ixonanthaceae, Sterculiaceae), and may also be found protecting perennating organs such as tubers and corms (e.g. Dioscorea prehensilis -Dioscoreaceae- and Moraea spp. -Iridaceae- respectively). [5] Short root spines cover the tuberous base of the epiphytic ant-plant Myrmecodia tuberosa (Rubiaceae), these probably give protection to ants which inhabit chambers within the tuber as they wander over the plant's surface. (Jackson 1986 [5] and references therein). In many respects, the pattern of spine formation is similar to that which occurs in the development of thorns from lateral shoots. (Jackson 1986 [5] and references therein).

Evolution

It has been proposed that thorny structures may have first evolved as a defense mechanism in plants growing in sandy environments that provided inadequate resources for fast regeneration of damage. [11] [12]

Morphological variation

Spinose structures occur in a wide variety of ecologies, and their morphology also varies greatly. They occur as:

Some thorns are hollow and act as myrmecodomatia; others (e.g. in Crataegus monogyna ) bear leaves. The thorns of many species are branched (e.g. in Crataegus crus-galli and Carissa macrocarpa ).

Human uses

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] [ page needed ]

See also

Related Research Articles

Cactus Family of mostly succulent plants, adapted to dry environments

A cactus is a member of the plant family Cactaceae, a family comprising about 127 genera with some 1750 known species of the order Caryophyllales. The word "cactus" derives, through Latin, from the Ancient Greek κάκτος, kaktos, a name originally used by Theophrastus for a spiny plant whose identity is now not certain. Cacti occur in a wide range of shapes and sizes. Most cacti live in habitats subject to at least some drought. Many live in extremely dry environments, even being found in the Atacama Desert, one of the driest places on earth. Cacti show many adaptations to conserve water. Almost all cacti are succulents, meaning they have thickened, fleshy parts adapted to store water. Unlike many other succulents, the stem is the only part of most cacti where this vital process takes place. Most species of cacti have lost true leaves, retaining only spines, which are highly modified leaves. As well as defending against herbivores, spines help prevent water loss by reducing air flow close to the cactus and providing some shade. In the absence of leaves, enlarged stems carry out photosynthesis. Cacti are native to the Americas, ranging from Patagonia in the south to parts of western Canada in the north—except for Rhipsalis baccifera, which also grows in Africa and Sri Lanka.

Shoot Young stem or branch

In botany, shoots consist of stems including their appendages, the leaves and lateral buds, flowering stems and flower buds. The new growth from seed germination that grows upward is a shoot where leaves will develop. In the spring, perennial plant shoots are the new growth that grows from the ground in herbaceous plants or the new stem or flower growth that grows on woody plants.

Meristem Type of plant tissue involved in cell proliferation

The meristem is a type of tissue found in plants. It consists of undifferentiated cells capable of cell division. Cells in the meristem can develop into all the other tissues and organs that occur in plants.

<i>Robinia pseudoacacia</i> Species of plant

Robinia pseudoacacia, commonly known in its native territory as black locust, is a medium-sized hardwood deciduous tree, belonging to the tribe Robinieae. It is endemic to a few small areas of the United States, but it has been widely planted and naturalized elsewhere in temperate North America, Europe, Southern Africa and Asia and is considered an invasive species in some areas. Another common name is false acacia, a literal translation of the specific name.

Trichome fine outgrowths or appendages on plants, algae, lichens, and certain protists. A unicellular or multicellular plant structure that forms a non-sclerified outgrowth from the epidermis

Trichomes, from the Greek τρίχωμα (trichōma) meaning "hair", are fine outgrowths or appendages on plants, algae, lichens, and certain protists. They are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae. A covering of any kind of hair on a plant is an indumentum, and the surface bearing them is said to be pubescent.

In botany, a stipule is an outgrowth borne on either side of the base of a leafstalk. A pair of stipules is considered part of the anatomy of the leaf of a typical flowering plant, although in many species the stipules are inconspicuous or entirely absent. In some older botanical writing, the term "stipule" was used more generally to refer to any small leaves or leaf-parts, notably prophylls. The word stipule was coined by Linnaeus from Latin stipula, straw, stalk.

Glossary of leaf morphology Wikipedia glossary

The following is a defined list of terms which are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple or compound. The edge of the leaf may be regular or irregular, may be smooth or bearing hair, bristles or spines. For more terms describing other aspects of leaves besides their overall morphology see the leaf article.

Areole Bumps on cacti out of which grow clusters of spines

In botany, areoles are small light- to dark-colored bumps on cacti out of which grow clusters of spines. Areoles are important diagnostic features of cacti, and identify them as a family distinct from other succulent plants. The spines are not easily detachable, but on certain cacti, members of the subfamily Opuntioideae, smaller, detachable bristles, glochids, also grow out of the areoles and afford additional protection.

<i>Kalanchoe beharensis</i> species of plant

Kalanchoe beharensis is a plant species in the succulent genus Kalanchoe, and the family Crassulaceae. Kalanchoe beharensis is native to Madagascar.

Epidermis (botany) outermost single layer of cells in plants. the outer protective layer of cells of a plant, which may be thickened by a cuticle

The epidermis is a single layer of cells that covers the leaves, flowers, roots and stems of plants. It forms a boundary between the plant and the external environment. The epidermis serves several functions: it protects against water loss, regulates gas exchange, secretes metabolic compounds, and absorbs water and mineral nutrients. The epidermis of most leaves shows dorsoventral anatomy: the upper (adaxial) and lower (abaxial) surfaces have somewhat different construction and may serve different functions. Woody stems and some other stem structures such as potato tubers produce a secondary covering called the periderm that replaces the epidermis as the protective covering.

Glochid Detachable, irritating spines on cacti of the sub-family Opuntioideae

Glochids or glochidia are hair-like spines or short prickles, generally barbed, found on the areoles of cacti in the sub-family Opuntioideae. Cactus glochids easily detached from the plant and lodge in the skin, causing irritation upon contact. The tufts of glochids in the areoles nearly cover the stem surfaces of some cactus species, each tuft containing hundreds of glochids; this may be in addition to, or instead of, the larger, more conspicuous cactus spines, which do not readily detach and are not generally barbed.

Plant defense against herbivory range of adaptations evolved by plants which improve their survival and reproduction by reducing the impact of herbivores; plant defensive strategies (defensive traits) to defend against damage caused by herbivores

Plant defense against herbivory or host-plant resistance (HPR) describes a range of adaptations evolved by plants which improve their survival and reproduction by reducing the impact of herbivores. Plants can sense being touched, and they can use several strategies to defend against damage caused by herbivores. Many plants produce secondary metabolites, known as allelochemicals, that influence the behavior, growth, or survival of herbivores. These chemical defenses can act as repellents or toxins to herbivores, or reduce plant digestibility.

Plant morphology Part of botany

Phytomorphology is the study of the physical form and external structure of plants. This is usually considered distinct from plant anatomy, which is the study of the internal structure of plants, especially at the microscopic level. Plant morphology is useful in the visual identification of plants.

This page provides a glossary of plant morphology. Botanists and other biologists who study plant morphology use a number of different terms to classify and identify plant organs and parts that can be observed using no more than a handheld magnifying lens. This page provides help in understanding the numerous other pages describing plants by their various taxa. The accompanying page—Plant morphology—provides an overview of the science of the external form of plants. There is also an alphabetical list: Glossary of botanical terms. In contrast, this page deals with botanical terms in a systematic manner, with some illustrations, and organized by plant anatomy and function in plant physiology.

Important structures in plant development are buds, shoots, roots, leaves, and flowers; plants produce these tissues and structures throughout their life from meristems located at the tips of organs, or between mature tissues. Thus, a living plant always has embryonic tissues. By contrast, an animal embryo will very early produce all of the body parts that it will ever have in its life. When the animal is born, it has all its body parts and from that point will only grow larger and more mature.

This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary of leaf morphology. For other related terms, see Glossary of phytopathology and List of Latin and Greek words commonly used in systematic names.

Plant stem structural axis of a vascular plant

A stem is one of two main structural axes of a vascular plant, the other being the root. It supports leaves, flowers and fruits, transports fluids between the roots and the shoots in the xylem and phloem, stores nutrients, and produces new living tissue.

Leaf Photosynthetic organ of a vascular plant

A leaf is the principal lateral appendage of the vascular plant stem, usually borne above ground and specialized for photosynthesis. The leaves and stem together form the shoot. Leaves are collectively referred to as foliage, as in "autumn foliage". In most leaves, the primary photosynthetic tissue, the palisade mesophyll, is located on the upper side of the blade or lamina of the leaf but in some species, including the mature foliage of Eucalyptus, palisade mesophyll is present on both sides and the leaves are said to be isobilateral. Most leaves are flattened and have distinct upper (adaxial) and lower (abaxial) surfaces that differ in color, hairiness, the number of stomata, the amount and structure of epicuticular wax and other features. Leaves are mostly green in color due to the presence of a compound called chlorophyll that is essential for photosynthesis as it absorbs light energy from the sun. A leaf with white patches or edges is called a variegated leaf.

Fascicle (botany) type of inflorescence

In botany, a fascicle is a bundle of leaves or flowers growing crowded together; alternatively the term might refer to the vascular tissues that supply such an organ with nutrients. However, vascular tissues may occur in fascicles even when the organs they supply are not fascicled.

<i>Dracaena pinguicula</i> species of plant

Dracaena pinguicula, synonym Sansevieria pinguicula, also known as the walking sansevieria, is a xerophytic CAM succulent native to the Bura area of Kenya, near Garissa. The species was described by Peter René Oscar Bally in 1943.

References

General references
Footnotes
  1. 1 2 3 4 5 6 7 8 9 10 Simpson, M. G. 2010. "Plant Morphology". In: Plant Systematics, 2nd. edition. Elsevier Academic Press. Chapter 9.
  2. 1 2 3 4 5 6 7 8 Judd, Campbell, Kellogg, Stevens, Donoghue. 2007. "Structural and Biochemical Characters". In: Plant Systematics, a phylogenetic approach, third edition. Chapter 4.
  3. 1 2 3 4 Turner et al. 2005, Sonoran Desert Plants, an Ecological Atlas. University of Arizona Press.
  4. 1 2 3 Van Wyk, Van Wyk. 2007. How to identify trees in South Africa. Struik.
  5. 1 2 3 4 5 6 7 8 9 10 11 12 Jackson, M. B. (ed.) 1986. New Root Formation in Plants and Cuttings. Series Developments in plant and soil sciences nº 20. Martinus Nijhoff Publishers, a member of the Kluwer Academic Publishers Group. Da ordrecht / Boston / Lancaster. p.80-81. https://books.google.com/books?id=gAv8CAAAQBAJ&pg=PA80
  6. Agrawal, A, A., Rudgers, A, J., Botsford, W, L., Cutler, S., Gorin, B, J., Lundquist, C, J., Spitzer, W, B., & Swann, L, A. (2000). Benefits and Constraints on Plant Defense against Herbivores: Spines Influence the Legitimate and Illegitimate Flower Visitors of Yellow Star Thistle, Centaurea solstitialis L. (Asteraceae). JSTOR, 45(1), 1-5. https://www.jstor.org/stable/3672545. retrieved 2012-03-20
  7. 1 2 Bell, A.D. 1997. Plant form: an illustrated guide to flowering plant morphology. Oxford University Press, Oxford, U.K. preview in google books
  8. Van Wyk, Braam (2007). How to Identify Trees in Southern Africa (illustrated ed.). Struik. p. 184. ISBN   9781770072404.
  9. Sengbusch, Peter (2003-07-31). "Cross-Section Through the Prickle of a Rose". Archived from the original on 2008-04-30. Retrieved 2009-04-27.
  10. Ross, J. H. "A conspectus of the African Acacia species." Series: Memoirs of the Botanical Survey of South Africa, No. 44 Botanical Research Institute, Dept. of Agricultural Technical Services, Pretoria, 1979
  11. Steve Brill, Evelyn Dean, Identifying and Harvesting Edible and Medicinal Plants (1994), p. 17.
  12. August Weismann, John Arthur Thomson, Margaret R. Thomson, The Evolution Theory (1904), p. 124.
  13. Bihrmann.com
  14. Dyer, R. Allen, “The Genera of Southern African Flowering Plants”, Vol 2. ISBN   0-621-02863-0, 1976
  15. Anderson, Edward F., The Cactus Family, Pub: Timber Press 2001 ISBN   978-0-88192-498-5
  16. Marcus Felson, Crime and Nature (2006), p. 288.
  17. Hunter, J. A., "Hunter" Publisher: Buccaneer Books, 1993, ISBN   978-1-56849-109-7