| Tar tree | |
|---|---|
 | |
| Fruits and foliage | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Sapindales |
| Family: | Anacardiaceae |
| Genus: | Semecarpus |
| Species: | S. australiensis |
| Binomial name | |
| Semecarpus australiensis | |
| Synonyms[3] | |
| |
Semecarpus australiensis, commonly known as thetar tree,native cashew,marking nut, orcedar plum, is a species of tree in the cashew and mango familyAnacardiaceae, native to parts ofMelanesia and northernAustralia. Contact with the plant can cause serious allergic reactions, a common characteristic of this family.
The tar tree is a large rainforest tree up to 40 m (130 ft) in height.[5][6] The trunk is generally straight and cylindrical, and marked with numerous oval-shapedlenticels arranged in more or less vertical lines. When cut or damaged the trunk and branches produce a tar-likeexudate which turns black on exposure to the air.[4][7]
The leaves are up to 30 cm (12 in) long by wide 12 cm (4.7 in)[4][7] with prominent pale yellow veins. They are dark green andglabrous on the upper surface and chalky blue-green (glaucous) underneath.[4][6]
The flowers arepentamerous and are quite small; petals on the male flowers are about 1.5 mm (0.059 in) long, while those on female flowers measure up to 4 mm (0.16 in) long.[4][5][7] Flowering occurs in spring (September to November) and fruits are produced through the summer.[8]
The fruits are atrue nut attached beneath a colourful fleshyreceptacle.[4][7] 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 orpedicel and is much larger than the nut (seeimages below). Neither are edible to humans in their raw state due to the presence of highly irritant resins.[9][10]
Semecarpus australiensis was first described by the German botanistAdolf Engler. His treatment was published in volume 4 ofMonographiae Phanerogamarum in 1883.[11]
The genus nameSemecarpus is from the Latinsemi-, meaning half, and the Ancient Greekκᾰρπός (karpós), meaning fruit. It is a reference to the appearance of the fruit. Thespecies epithet means "from Australia".[6]
The natural range ofSemecarpus australiensis is from theMoluccas in the west, intoNew Guinea, theBismark Archipelago,Vanuatu andNew Caledonia in the east; and south to the coastal parts of theNorthern Territory andQueensland in Australia.[3][4]
It grows in lowland rainforest,monsoon forest andgallery forest, close to the sea or to water courses.[4][5][10][12]
The fruits of this species are eaten bycassowaries (Casuarius casuarius)[4][6][10] 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 thePurple Line-blue butterfly (Prosotas dubiosa).[13]
Like many other species in the family Anacardiaceae, this tree may cause severe allergic responses after contact with it.[4][5][7][9][10] The agents responsible for the allergies areresinous phenolic compounds[14] found in most parts of the plant, including the fruits and theexudate from the trunk and branches.[14][15] Direct contact with the tree is not necessary to elicit the allergic response; in March 1954, an article appeared in the local newspaper inCairns, Australia, describing how a number of children suffered rashes after swimming in a stream beneath a tar tree.[16]
Indigenous Australians were are aware of the toxic nature of this plant, and kept their children away from it.[9] 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.[9][10][12] Even the smoke from the fire can cause problems, and they were careful to prepare the food well away from their camp.[9][10]
Media related toSemecarpus australiensis at Wikimedia Commons
Data related toSemecarpus australiensis at Wikispecies