A thicket is a very dense stand of trees or tall shrubs , often dominated by only one or a few species , to the exclusion of all others. They may be formed by species that shed large numbers of highly viable seeds that are able to germinate in the shelter of the maternal plants.
31-399: In some conditions, the formation or spread of thickets may be assisted by human disturbance of an area. Human disturbance and activity within thickets varies based on culture and location. Where a thicket is formed of briar (also spelled brier ), which is a common name for any of a number of unrelated thorny plants , it may be called a briar patch . Plants termed briar include species in
62-570: A defense mechanism in plants growing in sandy environments that provided inadequate resources for fast regeneration of damage. 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 ). Plants bearing thorns, spines, or prickles are often used as
93-492: A urent vestiture . There can be found also spines or spinose structures derived from roots. 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
124-659: A defense against burglary , being strategically planted below windows or around the entire perimeter of a property. They also have been used to protect crops and livestock against marauding animals. Examples include hawthorn hedges in Europe, agaves or ocotillos 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. Petiole (botany) In botany ,
155-459: A family in which the leaves are always sessile. In some other plant groups, such as the speedwell genus Veronica , petiolate and sessile leaves may occur in different species. In the grasses ( Poaceae ), the leaves are apetiolate, but the leaf blade may be narrowed at the junction with the leaf sheath to form a pseudopetiole , as in Pseudosasa japonica . In plants with compound leaves ,
186-467: 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: "...
217-520: A part of a leaf containing the petiole, midrib, or a secondary vein. 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 ). Prickles are comparable to hairs but can be quite coarse (for example, rose prickles). They are extensions of
248-519: A petiolule is called a pulvinulus. In some plants, the petioles are flattened and widened to become phyllodes (also known as phyllodia or cladophylls) and the true leaves may be reduced or absent. Thus, the phyllode comes to serve the functions of the leaf. Phyllodes are common in the genus Acacia , especially the Australian species, at one time put in Acacia subgenus Phyllodineae . In Acacia koa ,
279-567: A thicket's high plant density and resulting low visibility allows for predator species to succeed in tracking, stalking, and capturing their prey. Especially within the Albany thicket biome, thickets have traditionally been used for raising domestic livestock , although the popularity of doing so is declining over time. Recently, the primary human activity taking place in thickets is game hunting, both for recreational purposes and for ecotourism . The increase in game hunting within thickets has also led to
310-535: A thicket's lack of C4 grasses and relatively low fire exposure. While thickets tend to have a small number of plant species present, as they are often dominated by one species of tree or shrub, the biome provides ecological resources to a large group of species. Thickets frequently make up sections of the home ranges of native species, including ptarmigan and hares in the tundra, cheetahs and lions in Africa, and frogs and alligators in North America. In particular,
341-403: A ventilating function may also be found on roots of Iriartea exorrhiza . There are also spines that function as pneumorhizae on the palm Euterpe oleracea . In Cryosophila nana (formerly Acanthorhiza aculeata ), there are spiny roots; some authors prefer to term these "root spines" if the length of the root is less than 10x the thickness and "spine roots" if the length is more than 10x
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#1732852490252372-401: Is a stalk that attaches a leaf to the plant stem. In petiolate leaves the leaf stalk may be long (as in the leaves of celery and rhubarb ), or short (for example basil ). When completely absent, the blade attaches directly to the stem and is said to be sessile . Subpetiolate leaves have an extremely short petiole, and may appear sessile. The broomrape family Orobanchaceae is an example of
403-597: Is an effective manner in which to preserve land area and minimize human impact on a thicket. This botany article is a stub . You can help Misplaced Pages by expanding it . This article about environmental habitats is a stub . You can help Misplaced Pages by expanding it . Spine (botany) 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
434-448: The cortex and epidermis . Technically speaking, many plants commonly thought of as having thorns or spines actually have prickles. Roses , for instance, have prickles. While the position of thorns and spines are known positively to be controlled by phyllotaxis , the positioning of prickles appears to be truly random. If not, then by a phyllotaxis so arcane as to give the appearance of randomness. A study published for peer review to
465-478: The petiole ( / ˈ p iː t i . oʊ l / ) is the stalk that attaches the leaf blade to the stem . It is able to twist the leaf to face the sun, producing a characteristic foliage arrangement (spacing of blades), and also optimizing its exposure to sunlight. Outgrowths appearing on each side of the petiole in some species are called stipules . The terms petiolate and apetiolate are applied respectively to leaves with and without petioles. The petiole
496-423: The petiole or a stipule ), and prickles are derived from epidermis tissue (so that they can be found anywhere on the plant and do not have vascular bundles inside ). Leaf margins may also have teeth, and if those teeth are sharp, they are called spinose teeth on a spinose leaf margin (some authors consider them a kind of spine ). On a leaf apex, if there is an apical process (generally an extension of
527-446: The rhizome and produces the leaf at its end. Botanically, it is categorized as a vegetable but, culinarily, it is more often used as a fruit. The longest known petiole is that of the royal waterlily or iaupê jaçanã Victoria amazonica which is up to 23 ft (7.0 m) in length. 'Petiole' comes from Latin petiolus , or 'little foot', 'stem', an alternative diminutive of 'pes', 'foot'. The regular diminutive 'pediculus'
558-421: The bases of the living fronds) also alters during their life. They initially grow upwards and then turn down and finally they, too, become spinous. Lateral roots on these two types of roots, as well as those on the stilt roots on this species, also become spinous. Some authors believe that some of these short spiny laterals have a ventilating function so they are 'pneumorhizae'. Short spiny laterals that may have
589-468: The division of the African acacias on the basis of spinescent stipules versus non-spinescent stipules..." 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. The anatomy of crown roots on this species (roots among
620-412: The genera Rosa ( Rose ), Rubus , and Smilax . Thickets are characterized by dense plant life, a low closed canopy, deep shale-derived soil, and high levels of soil carbon and nitrogen. Plants present within a thicket generally reach a maximum of 4 to 6 meters in height. The boundaries between a thicket and its nearby forest are defined by a lack of precipitation and overall dry environment within
651-460: The journal Science concluded that plants with these types of prickles have been identified as sharing a common gene family. 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
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#1732852490252682-438: The leaflets are attached to a continuation of the petiole called the rachis . Each leaflet may be attached to the rachis by a short stalk called the petiolule. There may be swollen regions at either end of the petiole known as pulvina (singular = pulvinus ) that are composed of a flexible tissue that allows leaf movement. Pulvina are common in the bean family Fabaceae and the prayer plant family Marantaceae . A pulvinus on
713-448: 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 (again, some authors call them a kind of spine ). When the leaf epidermis is covered with very long, stiff trichomes (more correctly called bristles in this case; for some authors a kind of prickle ), it may be referred to as a hispid vestiture ; if the trichomes are stinging trichomes, it may be called
744-483: The phyllodes are leathery and thick, allowing the tree to survive stressful environments. The petiole allows partially submerged hydrophytes to have leaves floating at different depths, the petiole being between the node and the stem. In plants such as rhubarb ( Rheum rhabarbarum ), celery ( Apium graveolens ), artichokes , and cardoons ( Cynara cardunculus ), the petioles ('stalks' or 'ribs') are cultivated as edible crops. The petiole of rhubarb grows directly from
775-500: 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. Pointing or spinose processes can broadly be divided by
806-967: 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 branches or stems . They may be simple or branched. 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 . 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
837-426: The rise of manmade game farms , which has prompted discussion regarding the impact of game farms on the biome and its health. Conservationists and biologists pose concern about the decrease in biodiversity that game farms may create, especially when coupled with other anthropogenic threats to thickets such as land clearing and urbanization . Alternatively, farmers and many locals suggest that the formation of game farms
868-438: The same function: physically defending plants against herbivory . 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), spines are derived from leaves (either the entire leaf or some part of the leaf that has vascular bundles inside, like
899-689: The thicket area, while forests receive higher levels of precipitation. Forests also do not experience as much herbivory and browsing in comparison to thickets. The thicket biome has been identified in Africa, Madagascar, Australia, North America, and South America. One of the most studied and well-recognized thickets is the Albany thicket biome, located in the Eastern Cape of South Africa. Due to their overlapping ranges and similarity of plant species, thicket biomes may be misidentified as being portions of savannas . However, these areas can be differentiated through
930-497: The thickness. 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). Short root spines cover
961-484: 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 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 and references therein). It has been proposed that thorny structures may have first evolved as