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 mainlan ...

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 sout ...

. 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 ''Sassafras'' is a genus of three extant and one extinct species of deciduous trees in the family Lauraceae, native to eastern North America and eastern Asia.Wolfe, Jack A. & Wehr, Wesley C. 1987. The sassafras is an ornamental tree. "Middle ...

'', 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 ''Cassytha'' is a genus of some two dozen species of obligately parasitic vines in the family Lauraceae. Superficially, and in some aspects of their ecology, they closely resemble plants in the unrelated genus ''Cuscuta'', the dodders.Web ...

'' is unique in the Lauraceae in that its members are

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson ha ...

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 Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures fall as elevation increases, causing the ecosystem to stratify. This stratification is a crucial ...

. 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 The Magnoliaceae () are a flowering plant family, the magnolia family, in the order Magnoliales. It consists of two genera: ''Magnolia'' and '' Liriodendron'' (tulip trees). Unlike most angiosperms, whose flower parts are in whorls (rings), t ...

or Myrtaceae. 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 ''

'', all of which are obligately

s. The fruits of Lauraceae are drupes, one-seeded fleshy fruit with a hard layer, the

endocarp Fruit anatomy is the plant anatomy of the internal structure of fruit. Fruits are the mature ovary or ovaries of one or more flowers. They are found in three main anatomical categories: aggregate fruits, multiple fruits, and simple fruits. Aggr ...

, 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 A cupule is a small structure shaped like a cup, including: * In archeology, rock cupules are circular man-made hollows on the surface of a large rock or a rock slab ** On a smaller artifact they are called a cupstone. * In botany: the base of an ...

, 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 Dried fruits of ''Lindera neesiana'' used as spice (coll. MHNT) ''Lindera'' is a genus of about 80–100hypocarpium 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 o ...

at the base of the fruit.

Distribution and uses

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

supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", which leav ...

, modern species commonly occur in

relict A relict is a surviving remnant of a natural phenomenon. Biology A relict (or relic) is an organism that at an earlier time was abundant in a large area but now occurs at only one or a few small areas. Geology and geomorphology In geology, a r ...

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 (ecology ...

and

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

in communities of great value in inferring the

palaeontological Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

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 An essential oil is a concentrated hydrophobic liquid containing volatile (easily evaporated at normal temperatures) chemical compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetheroleum, or simply as the o ...

, 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 A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...

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 vo ...

, 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 a s ...

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 A cabinet is a case or cupboard with shelves and/or drawers for storing or displaying items. Some cabinets are stand alone while others are built in to a wall or are attached to it like a medicine cabinet. Cabinets are typically made of wood (so ...

, 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, Cinnamomum cassia, cassia and Cinnamomum camphora, camphor laurel *''Laurus'': bay laurel *''Persea'': avocado Loss of habitat and overexploitation for such products has put many species in endangered species, danger of extinction as a result of overcutting, extensive illegal logging, 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. 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, 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 (Biological dispersal, ornithochory). Some other birds that swallow the fruit pass the seed intact through their guts. Seed dispersal of various species in the family is also carried out by monkeys, Arboreal locomotion, arboreal rodents, porcupines, opossums, and fishes. Seed dispersal, Hydrochory occurs in ''Caryodaphnopsis''. The leaves of some species in the Lauraceae have domatia in the axils of their Veinlets, veins. The domatia are home to certain mites. Other lauraceous species, members of the genus ''Pleurothyrium'' in particular, have a symbiosis, symbiotic 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

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 forest, and in Africa for example there are species endemic to countries such as Cameroon, Sudan, Tanzania, Uganda and Democratic Republic of the Congo, Congo. Several

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, 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 (plant), Daphne'' (e.g., ''Daphnidium'', ''Daphniphyllum'') or "laurel" (e.g.,''Laureliopsis'', ''Skimmia laureola'') 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. Paleobotany, 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. Fossil flowers attributed to this family occur in Cenomanian clays (mid-Cretaceous, 90-98 Mya) of the Eastern United States (''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. 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 in tropical, subtropical, and arid regions. Laurel wilt disease, caused by the virulent fungal pathogen ''Raffaelea lauricola'', a native of South Asia, southern Asia, was found in the southeast United States in 2002. The fungus spreads between hosts via a wood-boring beetle, ''Xyleborus glabratus'', with which it has a symbiotic 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 Specialization (biology), specializations, including defensive or deterrent systems against other organisms. Phytochemicals in the Lauraceae are numerous and diverse. Benzylisoquinoline alkaloids include aporphines and oxoaporphines, as well as derivatives of morphinans. Essential oils include terpenoids, benzyl benzoates, allylphenols, and Phenylpropene, propenylphenols. Lignans and neolignans are present, along with ''S''-methyl-5-O-flavonoids, proanthocyanidins, cinnamoylamides, phenylpyrroles, styryl pyrones, polyketides (acetogenins), furanosesquiterpenes, and Germacranolide, germacranolidous, heliangolide, heliangolidous, eudesmanolide, eudesmanolidous and guaianolide, 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, and is associated in some countries with academic or literary achievement.