''Semecarpus australiensis'', commonly known as the tar tree, native cashew, marking nut, or cedar plum, is a species of tree in the cashew and mango family

Anacardiaceae The Anacardiaceae, commonly known as the cashew family or sumac family, are a family of flowering plants, including about 83 genera with about 860 known species. Members of the Anacardiaceae bear fruits that are drupes and in some cases produce ...

, native to parts of

Melanesia Melanesia (, ) is a subregion of Oceania in the southwestern Pacific Ocean. It extends from New Guinea in the west to the Fiji Islands in the east, and includes the Arafura Sea. The region includes the four independent countries of Fiji, Vanu ...

and northern

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

. Contact with the plant can cause serious allergic reactions, a common characteristic of this family.

Description

The tar tree is a large rainforest tree up to in height. The trunk is generally straight and cylindrical, and marked with numerous oval-shaped

lenticel A lenticel is a porous tissue consisting of cells with large intercellular spaces in the periderm of the secondarily thickened organs and the Bark (botany), bark of woody stems and roots of gymnosperms and dicotyledonous flowering plants. It func ...

s arranged in more or less vertical lines. When cut or damaged the trunk and branches produce a tar-like

exudate An exudate is a fluid released by an organism through pores or a wound, a process known as exuding or exudation. ''Exudate'' is derived from ''exude'' 'to ooze' from Latin language, Latin 'to (ooze out) sweat' (' 'out' and ' 'to sweat'). Medi ...

which turns black on exposure to the air. The leaves are up to long by wide with prominent pale yellow veins. They are dark green and

glabrous Glabrousness () is the technical term for a lack of hair, down, setae, trichomes, or other such covering. A glabrous surface may be a natural characteristic of all or part of a plant or animal, or be due to loss because of a physical condition, ...

on the upper surface and chalky blue-green (

glaucous ''Glaucous'' (, ) is used to describe the pale grey or bluish-green appearance of the surfaces of some plants, as well as in the names of birds, such as the glaucous gull (''Larus hyperboreus''), glaucous-winged gull (''Larus glaucescens''), ...

) underneath. The flowers are pentamerous and are quite small; petals on the male flowers are about long, while those on female flowers measure up to long. Flowering occurs in spring (September to November) and fruits are produced through the summer. The fruits are a

true nut A nut is a fruit consisting of a hard or tough nutshell protecting a kernel which is usually edible. In general usage and in a culinary sense, many dry seeds are called nuts, but in a botanical context, "nut" implies that the shell does not open ...

attached beneath a colourful fleshy receptacle. To the casual observer it appears to be a "fruit" (the receptacle) with a "seed" (the nut) on the outside. The receptacle is actually the swollen flower stem or

pedicel Pedicle or pedicel may refer to: Human anatomy *Pedicle of vertebral arch, the segment between the transverse process and the vertebral body, and is often used as a radiographic marker and entry point in vertebroplasty and kyphoplasty procedures ...

and is much larger than the nut (see

images An image or picture is a visual representation. An image can be two-dimensional, such as a drawing, painting, or photograph, or three-dimensional, such as a carving or sculpture. Images may be displayed through other media, including a project ...

below). Neither are edible to humans in their raw state due to the presence of highly irritant resins.

Taxonomy

''Semecarpus australiensis'' was first described by the German botanist

Adolf Engler Heinrich Gustav Adolf Engler (25 March 1844 – 10 October 1930) was a German botanist. He is notable for his work on plant taxonomy and phytogeography, such as ''Die natürlichen Pflanzenfamilien'' (''The Natural Plant Families''), edited with K ...

. His treatment was published in volume 4 of ''Monographiae Phanerogamarum'' in 1883.

Etymology

The genus name ''Semecarpus'' is from the Latin ''semi-'', meaning half, and the Ancient Greek ''κᾰρπός (karpós)'', meaning fruit. It is a reference to the appearance of the fruit. The

species epithet Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In Taxonomy (biology), taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany) ...

means "from Australia".

Distribution and habitat

The natural range of ''Semecarpus australiensis'' is from the

Moluccas The Maluku Islands ( ; , ) or the Moluccas ( ; ) are an archipelago in the eastern part of Indonesia. Tectonically they are located on the Halmahera Plate within the Molucca Sea Collision Zone. Geographically they are located in West Melanesi ...

in the west, into

New Guinea New Guinea (; Hiri Motu: ''Niu Gini''; , fossilized , also known as Papua or historically ) is the List of islands by area, world's second-largest island, with an area of . Located in Melanesia in the southwestern Pacific Ocean, the island is ...

, the Bismark Archipelago,

Vanuatu Vanuatu ( or ; ), officially the Republic of Vanuatu (; ), is an island country in Melanesia located in the South Pacific Ocean. The archipelago, which is of volcanic origin, is east of northern Australia, northeast of New Caledonia, east o ...

and

New Caledonia New Caledonia ( ; ) is a group of islands in the southwest Pacific Ocean, southwest of Vanuatu and east of Australia. Located from Metropolitan France, it forms a Overseas France#Sui generis collectivity, ''sui generis'' collectivity of t ...

in the east; and south to the coastal parts of the

Northern Territory The Northern Territory (abbreviated as NT; known formally as the Northern Territory of Australia and informally as the Territory) is an states and territories of Australia, Australian internal territory in the central and central-northern regi ...

and

Queensland Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...

in Australia. It grows in lowland rainforest,

monsoon forest Seasonal tropical forest, also known as moist deciduous, semi-evergreen seasonal, tropical mixed or monsoon forest, typically contains a range of tree species: only some of which drop some or all of their leaves during the dry season. This tropic ...

and

gallery forest A gallery forest is one formed as a corridor along rivers or wetlands, projecting into landscapes that are otherwise only sparsely treed such as savannas, grasslands, or deserts. The gallery forest maintains a more temperate microclimate above th ...

, close to the sea or to water courses.

Ecology

The fruits of this species are eaten by

cassowaries Cassowaries (; Biak language, Biak: ''man suar'' ; ; Papuan_languages, Papuan: ''kasu weri'' ) are flightless birds of the genus ''Casuarius'', in the order Casuariiformes. They are classified as ratites, flightless birds without a keel (bird a ...

(''Casuarius casuarius'') with no apparent adverse effects from the sap that is toxic to humans. The tree also serves as one of the host plants for the larvae of the Purple Line-blue butterfly (''Prosotas dubiosa'').

Toxicity

Like many other species in the family Anacardiaceae, this tree may cause severe allergic responses after contact with it. The agents responsible for the allergies are resinous phenolic compounds found in most parts of the plant, including the fruits and the

from the trunk and branches. Direct contact with the tree is not necessary to elicit the allergic response; in March 1954, an article appeared in the local newspaper in

Cairns Cairns (; ) is a city in the Cairns Region, Queensland, Australia, on the tropical north east coast of Far North Queensland. In the , Cairns had a population of 153,181 people. The city was founded in 1876 and named after William Cairns, Sir W ...

, Australia, describing how a number of children suffered rashes after swimming in a stream beneath a tar tree.

Indigenous uses

Indigenous Australians Indigenous Australians are people with familial heritage from, or recognised membership of, the various ethnic groups living within the territory of contemporary Australia prior to History of Australia (1788–1850), British colonisation. The ...

were are aware of the toxic nature of this plant, and kept their children away from it. They also knew that the fleshy receptacle and the nut (which is similar to the cashew) were edible, and they developed methods of deactivating the toxins so that they could be eaten. These included covering the hands with clay before handling the plant, and roasting the nuts in a fire. Even the smoke from the fire can cause problems, and they were careful to prepare the food well away from their camp.

Gallery

File:Semecarpus-australiensis-SF21353-02.jpg , Mature fruit File:Semecarpus-australiensis-SF21349.jpg , Detail of trunk File:Semecarpus australiensis leaves SF21170.jpg , Foliage File:Semecarpus australiensis exudate SF21170.jpg , Branch with black exudate

References

External links

* *
View a map
of recorded sightings of this species at the

Australasian Virtual Herbarium The ''Australasian Virtual Herbarium'' (AVH) is an online resource that allows access to plant specimen data held by various Australian and New Zealand herbaria. It is part of the Atlas of Living Australia (ALA), and was formed by the amalgama ...

View observations
of this species on

iNaturalist iNaturalist is an American 501(c)(3) nonprofit social network of naturalists, citizen scientists, and biologists built on the concept of mapping and sharing observations of biodiversity across the globe. iNaturalist may be accessed via its web ...

See images
of this species on Flickriver {{Taxonbar, from=Q7449189 australiensis Taxa named by Adolf Engler Plants described in 1883 Flora of Malesia Flora of Melanesia Flora of the Northern Territory Flora of Queensland Bushfood