Lauraceae, or the laurels, is a plant

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

that includes the true laurel and its closest relatives. This family comprises about 2850 known species in about 45 genera worldwide (Christenhusz & Byng 2016 ). They are dicotyledons, and occur mainly in warm temperate and tropical regions, especially

Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical south-eastern region of Asia, consisting of the regions that are situated south of mainland ...

and

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...

. Many are aromatic

evergreen In botany, an evergreen is a plant which has foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm climates, and contrasts with deciduous plants, whic ...

trees or shrubs, but some, such as '' Sassafras'', are

deciduous In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, ...

, or include both deciduous and evergreen trees and shrubs, especially in tropical and temperate climates. The genus '' Cassytha'' is unique in the Lauraceae in that its members are parasitic

vine A vine (Latin ''vīnea'' "grapevine", "vineyard", from ''vīnum'' "wine") is any plant with a growth habit of trailing or scandent (that is, climbing) stems, lianas or runners. The word ''vine'' can also refer to such stems or runners themsel ...

s. Most laurels are highly-poisonous.

Overview

The family has a worldwide distribution in tropical and warm climates. The Lauraceae are important components of tropical

forest A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' ...

s ranging from low-lying to montane. In several forested regions, Lauraceae are among the top five families in terms of the number of species present. The Lauraceae give their name to habitats known as laurel forests, which have many trees that superficially resemble the Lauraceae, though they may belong to other plant families such as Magnoliaceae or

Myrtaceae Myrtaceae, the myrtle family, is a family of dicotyledonous plants placed within the order Myrtales. Myrtle, pōhutukawa, bay rum tree, clove, guava, acca (feijoa), allspice, and eucalyptus are some notable members of this group. All sp ...

. Laurel forests of various types occur on most continents and on many major islands. Although the taxonomy of the Lauraceae is still not settled, conservative estimates suggest some 52 genera worldwide, including 3,000 to 3,500 species. Compared to other plant families, the taxonomy of Lauraceae still is poorly understood. This is partly due to its great diversity, the difficulty of identifying the species, and partly because of inadequate investment in taxonomic work. Recent monographs on small and medium-sized genera of Lauraceae (up to about 100 species) have revealed many new species. Similar increases in the numbers of species recognised in other larger genera are to be expected.

Description

Most of the Lauraceae are evergreen

tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...

s in

habit A habit (or wont as a humorous and formal term) is a routine of behavior that is repeated regularly and tends to occur subconsciously.

. Exceptions include some two dozen species of '' Cassytha'', all of which are obligately parasitic

s. The fruits of Lauraceae are drupes, one-seeded fleshy fruit with a hard layer, the endocarp, surrounding the seed. However, the endocarp is very thin, so the fruit resemble a one-seeded berry. The fruit in some species (particularly in the genera ''Ocotea'' and ''Oreodaphne'') are partly immersed or covered in a cup-shaped or deep thick cupule, which is formed from the tube of the calyx where the peduncle joins the fruit; this gives the fruit an appearance similar to an acorn. In some '' Lindera'' species, the fruit have a hypocarpium at the base of the fruit.

Distribution and uses

Because the family is so ancient and was so widely distributed on the

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final sta ...

supercontinent, modern species commonly occur in relict populations isolated by geographical barriers, for instance on islands or tropical mountains. Relict forests retain

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...

fauna Fauna is all of the animal life present in a particular region or time. The corresponding term for plants is '' flora'', and for fungi, it is '' funga''. Flora, fauna, funga and other forms of life are collectively referred to as '' biota''. ...

and

flora Flora is all the plant life present in a particular region or time, generally the naturally occurring ( indigenous) native plants. Sometimes bacteria and fungi are also referred to as flora, as in the terms '' gut flora'' or '' skin flora''. ...

in communities of great value in inferring the palaeontological succession and

climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...

that followed the breakups of the supercontinents. *Many Lauraceae contain high concentrations of essential oils, some of which are valued for spices and perfumes. Within the plants, most such substances are components of irritant or toxic sap or tissues that repel or poison many herbivorous or parasitic organisms. *Some of the essential oils are valued as

fragrances An aroma compound, also known as an odorant, aroma, fragrance or flavoring, is a chemical compound that has a smell or odor. For an individual chemical or class of chemical compounds to impart a smell or fragrance, it must be sufficiently v ...

, such as in the traditional

laurel wreath A laurel wreath is a round wreath made of connected branches and leaves of the bay laurel (), an aromatic broadleaf evergreen, or later from spineless butcher's broom ('' Ruscus hypoglossum'') or cherry laurel ('' Prunus laurocerasus''). It is ...

classical antiquity Classical antiquity (also the classical era, classical period or classical age) is the period of cultural history between the 8th century BC and the 5th century AD centred on the Mediterranean Sea, comprising the interlocking civilizations of ...

, or in cabinet making, where the fragrant woods are prized for making insect-repellant furniture chests. *Some are valued in cooking, for example,

bay leaves The bay leaf is an aromatic leaf commonly used in cooking. It can be used whole, either dried or fresh, in which case it is removed from the dish before consumption, or less commonly used in ground form. It may come from several species of tr ...

are a popular ingredient in European, American, and Asian cuisines. *Avocados are important oil-rich fruit that are cultivated in warm climates around the world. *Many species are exploited for timber. *Some species are valued as sources of medicinal material. These genera include some of the best-known species of particular commercial value: *'' Cinnamomum'': cinnamon, cassia and

camphor laurel ''Camphora officinarum'' is a species of evergreen tree that is commonly known under the names camphor tree, camphorwood or camphor laurel. Description ''Camphora officinarum'' is native to China south of the Yangtze River, Taiwan, southern ...

*'' Laurus'': bay laurel *'' Persea'':

avocado The avocado (''Persea americana'') is a medium-sized, evergreen tree in the laurel family ( Lauraceae). It is native to the Americas and was first domesticated by Mesoamerican tribes more than 5,000 years ago. Then as now it was prized for ...

Loss of habitat and overexploitation for such products has put many species in

danger Danger is a lack of safety and may refer to: Places * Danger Cave, an archaeological site in Utah * Danger Island, Great Chagos Bank, Indian Ocean * Danger Island, alternate name of Pukapuka Atoll in the Cook Islands, Pacific Ocean * Danger Is ...

of extinction as a result of overcutting, extensive

illegal logging Illegal logging is the harvest, transportation, purchase or sale of timber in violation of laws. The harvesting procedure itself may be illegal, including using corrupt means to gain access to forests; extraction without permission, or from a ...

, and habitat conversion. Conversely, some species, though commercially valuable in some countries, are regarded as aggressive invaders in other regions. For example, ''Cinnamomum camphora'', though a valued ornamental and medicinal plant, is so invasive as to have been declared a weed in subtropical forested areas of South Africa.

Ecology

Lauraceae flowers are protogynous, often with a complex flowering system to prevent

inbreeding Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically. By analogy, the term is used in human reproduction, but more commonly refers to the genetic disorders a ...

. The fruits are an important food source for birds, on which some Palaeognathae are highly dependent. Other birds that rely heavily on the fruit for their diets include members of the families Cotingidae,

Columbidae Columbidae () is a bird family consisting of doves and pigeons. It is the only family in the order Columbiformes. These are stout-bodied birds with short necks and short slender bills that in some species feature fleshy ceres. They primarily ...

, Trogonidae, Turdidae, and Ramphastidae, amongst others. Birds that are specialised frugivores tend to eat the whole fruit and regurgitate seeds intact, thereby releasing the seeds in favourable situations for germination ( ornithochory). Some other birds that swallow the fruit pass the seed intact through their guts.

Seed dispersal In Spermatophyte plants, seed dispersal is the movement, spread or transport of seeds away from the parent plant. Plants have limited mobility and rely upon a variety of dispersal vectors to transport their seeds, including both abiotic vector ...

of various species in the family is also carried out by

monkey Monkey is a common name that may refer to most mammals of the infraorder Simiiformes, also known as the simians. Traditionally, all animals in the group now known as simians are counted as monkeys except the apes, which constitutes an incomple ...

s, arboreal

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...

porcupine Porcupines are large rodents with coats of sharp spines, or quills, that protect them against predation. The term covers two families of animals: the Old World porcupines of family Hystricidae, and the New World porcupines of family, Erethiz ...

opossum Opossums () are members of the marsupial order Didelphimorphia () endemic to the Americas. The largest order of marsupials in the Western Hemisphere, it comprises 93 species in 18 genera. Opossums originated in South America and entered No ...

s, and

fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

es.

Hydrochory In Spermatophyte plants, seed dispersal is the movement, spread or transport of seeds away from the parent plant. Plants have limited mobility and rely upon a variety of dispersal vectors to transport their seeds, including both abiotic vectors, ...

occurs in '' Caryodaphnopsis''. The leaves of some species in the Lauraceae have domatia in the axils of their

veins Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated ...

. The domatia are home to certain

mite Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear e ...

s. Other lauraceous species, members of the genus '' Pleurothyrium'' in particular, have a

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or para ...

relationship with ants that protect and defend the tree. Some '' Ocotea'' species are also used as nesting sites by ants, which may live in leaf pockets or in hollowed-out stems. Defense mechanisms that occur among members of the Lauraceae include irritant or toxic sap or tissues that repel or poison many herbivorous organisms. Trees of the family predominate in the world's laurel forests and cloud forests, which occur in tropical to mild temperate regions of both northern and southern hemispheres. Other members of the family however, occur pantropically in general lowland and

Afromontane The Afromontane regions are subregions of the Afrotropical realm, one of the Earth's eight biogeographic realms, covering the plant and animal species found in the mountains of Africa and the southern Arabian Peninsula. The Afromontane regions of ...

forest, and in Africa for example there are species endemic to countries such as

Cameroon Cameroon (; french: Cameroun, ff, Kamerun), officially the Republic of Cameroon (french: République du Cameroun, links=no), is a country in west-central Africa. It is bordered by Nigeria to the west and north; Chad to the northeast; the ...

Sudan Sudan ( or ; ar, السودان, as-Sūdān, officially the Republic of the Sudan ( ar, جمهورية السودان, link=no, Jumhūriyyat as-Sūdān), is a country in Northeast Africa. It shares borders with the Central African Republic t ...

Tanzania Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands ...

Uganda }), is a landlocked country in East Africa. The country is bordered to the east by Kenya, to the north by South Sudan, to the west by the Democratic Republic of the Congo, to the south-west by Rwanda, and to the south by Tanzania. The ...

and Congo. Several relict species in the Lauraceae occur in temperate areas of both hemispheres. Many botanical species in other families have similar foliage to the Lauraceae due to

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...

, and forests of such plants are called laurel forest. These plants are adapted to high rainfall and humidity, and have leaves with a generous layer of wax, making them glossy in appearance, and a narrow, pointed-oval shape with a 'drip tip', which permits the leaves to shed water despite the humidity, allowing transpiration to continue. Scientific names similar to '' Daphne'' (e.g., '' Daphnidium'', '' Daphniphyllum'') or "laurel" (e.g.,''

Laureliopsis ''Laureliopsis'' is a genus of flowering plants with just one species, ''Laureliopsis philippiana'', known as tepa and wawán, endemic to Chile and the narrow neighboring strip of Argentina (35 to 45°S). In Chile it is found from Maule to Aysé ...

'', ''

Skimmia laureola ''Skimmia laureola'' is a species of shrub grown as an ornamental plant. The leaves are edible when cooked. The leaves give an aromatic smell when crushed. It produces white flowers that develop into small round red berries. The berries are eaten ...

'') indicate other plant families that resemble Lauraceae. Some Lauraceae species have adapted to demanding conditions in semiarid climates, but they tend to depend on favorable edaphic conditions, for example, perennial aquifers, periodic groundwater flows, or periodically flooded forests in sand that contains hardly any nutrients. Various species have adapted to swampy conditions by growing pneumatophores, roots that grow upward, that project above the levels of periodic floods that drown competing plants which lack such adaptations. Paleobotanists have suggested the family originated some 174±32 million years ago (Mya), while others do not believe they are older than the mid-

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

. Fossil flowers attributed to this family occur in

Cenomanian The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in ...

clays (mid-Cretaceous, 90-98 Mya) of the Eastern

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

(''Mauldinia mirabilis''). Fossils of Lauraceae are common in the Tertiary strata of Europe and North America, but they virtually disappeared from central Europe in the Late

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

. Because of their unusual fragility, the pollens of Lauraceae do not keep well and have been found only in relatively recent strata. Deciduous Lauraceae lose all of their leaves for part of the year depending on variations in rainfall. The leaf loss coincides with the

dry season The dry season is a yearly period of low rainfall, especially in the tropics. The weather in the tropics is dominated by the tropical rain belt, which moves from the northern to the southern tropics and back over the course of the year. The ...

in tropical, subtropical, and arid regions. Laurel wilt disease, caused by the virulent fungal pathogen ''Raffaelea lauricola'', a native of southern Asia, was found in the southeast United States in 2002. The fungus spreads between hosts via a wood-boring beetle, ''

Xyleborus glabratus ''Xyleborus glabratus'', the redbay ambrosia beetle, is a type of ambrosia beetle invasive in the United States. It has been documented as the primary vector of ''Raffaelea lauricola'', the fungus that causes laurel wilt, a disease that can ki ...

'', with which it has a

relationship. Several Lauraceae species are affected. The beetle and disease are believed to have arrived in the US via infected solid wood packing material, and have since spread to several states.http://www.ars.usda.gov/SP2UserFiles/Place/00000000/opmp/Redbay%20Laurel%20Wilt%20Recovery%20Plan%20January%202015.pdf

Classification

Classification within the Lauraceae is not fully resolved. Multiple classification schemes based on a variety of morphological and anatomical characteristics have been proposed, but none are fully accepted. According to Judd et al. (2007), the suprageneric classification proposed by van der Werff and Richter (1996) is currently the authority. However, due to an array of molecular and embryological evidence that disagrees with the groupings, it is not fully accepted by the scientific community. Their classification is based on inflorescence structure and wood and bark anatomy. It divides Lauraceae into two subfamilies, Cassythoideae and Lauroideae. The Cassythoideae comprise a single genus, ''Cassytha'', and are defined by their herbaceous, parasitic habit. The Lauroideae are then divided into three tribes: Laureae, Perseeae, and Cryptocaryeae. The subfamily Cassythoideae is not fully supported. Backing has come from ''matK'' sequences of chloroplast genes while a questionable placement of ''Cassytha'' has been concluded from analysis of intergenetic spacers of chloroplast and nuclear genomes. Embryological studies also appear contradictory. One study by Heo et al. (1998) supports the subfamily. It found that ''Cassytha'' develops an ''ab initio'' cellular-type endosperm and the rest of the family (with one exception) develops a nuclear-type endosperm. Kimoto et al. (2006) suggest ''Cassytha'' should be placed in the tribe Cryptocaryeae because it shares a glandular anther tapetum and an embryo sac protruding from the nucellus with other members of the Cryptocaryeae. The tribes Laureae and Perseeae are not well supported by any molecular or embryological studies. Sequences of the ''matK'' chloroplast gene, as well as sequences of chloroplast and nuclear genomes, reveal close relationships between the two tribes. Embryological evidence does not support a clear division between the two tribes, either. Genera such as ''Caryodaphnopsis'' and ''Aspidostemon'' that share embryological characteristics with one tribe and wood and bark characteristics or inflorescence characteristics with another tribe blur the division of these groups. All available evidence, except for inflorescence morphology and wood and bark anatomy, fails to support separate tribes Laureae and Perseeae. The tribe Cryptocaryeae is partially supported by molecular and embryological studies. Chloroplast and nuclear genomes support a tribal grouping that contains all the genera circumscribed by van der Weff and Richter (1996), as well as three additional genera. Partial support for the tribe is also attained from the ''matK'' sequences of chloroplast genes as well as embryology. Challenges in Lauraceae classification The knowledge of the species comprising the Lauraceae is incomplete. In 1991, about 25-30% of neotropical Lauraceae species had not been described. In 2001, embryological studies had only been completed on individuals from 26 genera yielding a 38.9% level of knowledge, in terms of embryology, for this family. Additionally, the huge amount of variation within the family poses a major challenge for developing a reliable classification.

Phytochemistry

The adaptation of Lauraceae to new environments has followed a long evolutionary journey which has led to many specializations, including defensive or deterrent systems against other organisms. Phytochemicals in the Lauraceae are numerous and diverse.

Benzylisoquinoline Substitution of the heterocycle isoquinoline at the C1 position by a benzyl group provides 1‑benzylisoquinoline, the most widely examined of the numerous benzylisoquinoline structural isomers. The 1-benzylisoquinoline moiety can be identified w ...

alkaloid Alkaloids are a class of basic, naturally occurring organic compounds that contain at least one nitrogen atom. This group also includes some related compounds with neutral and even weakly acidic properties. Some synthetic compounds of simila ...

s include aporphines and oxoaporphines, as well as derivatives of

morphinan Morphinan is the prototype chemical structure of a large chemical class of psychoactive drugs, consisting of opiate analgesics, cough suppressants, and dissociative hallucinogens, among others. Structure Morphinan has a phenanthrene core struct ...

s. Essential oils include terpenoids,

benzyl benzoate Benzyl benzoate is an organic compound which is used as a medication and insect repellent. As a medication it is used to treat scabies and lice. For scabies either permethrin or malathion is typically preferred. It is applied to the skin as a ...

s, allylphenols, and propenylphenols. Lignans and

neolignan The lignans are a large group of low molecular weight polyphenols found in plants, particularly seeds, whole grains, and vegetables. The name derives from the Latin word for "wood". Lignans are precursors to phytoestrogens. They may play a role ...

s are present, along with ''S''-methyl-5-O- flavonoids, proanthocyanidins, cinnamoylamides, phenylpyrroles, styryl pyrones, polyketides ( acetogenins), furanosesquiterpenes, and germacranolidous, heliangolidous, eudesmanolidous and guaianolidous sesquiterpene lactones.

Genera

Recent taxonomic revisions of the family include these genera: These genera have traditionally been considered separate within Lauraceae, but have not been included in the most recent treatments:

Popular culture

, a round or horseshoe-shaped wreath made of connected laurel branches and leaves, is an ancient symbol of triumph in classical Western culture originating in

Greek mythology A major branch of classical mythology, Greek mythology is the body of myths originally told by the ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the origin and nature of the world, the lives and activities o ...

, and is associated in some countries with academic or literary achievement.