Pittosporum Tobira

''Pittosporum tobira'' is a species of sweet-smelling flowering plant in the pittosporum family Pittosporaceae known by several common names, including Australian laurel, Japanese pittosporum, mock orange and Japanese cheesewood. It is native to Japan (south of Kanto), China, Taiwan, and Korea, but it is used throughout the world as an ornamental plant in landscaping and as cut foliage.

Description

It is an evergreen shrub which can reach tall by broad, and can become treelike. It can also be trimmed into a hedge. The leaves are oval in shape with edges that curl under and measure up to in length. They are leathery, hairless, and darker and shinier on the upper surfaces. The inflorescence is a cluster of fragrant flowers occurring at the ends of branches. The flower has five white petals each about a centimetre long. The fruit is a hairy, woody capsule about 1 cm wide divided into three valves. Inside are black seeds in a bed of resinous pulp.

Distribution

It is native to parts of Eastern Asia but has been introduced as an ornamental plant in many parts of the world. In China, it is found in the Fujian province and has been introduced in several others. In Japan, it is found in Honshu and the islands of Kyushu, Shikoku, as well as the Ryukyu Islands. It is also found in South Korea and northern Taiwan. It has been introduced to parts of the United States, and may be found in California, North Carolina, Georgia, and Florida.

It grows in forests, limestone areas, slopes, sandy seashores, and roadsides, usually to 1800 m sea level.

Taxonomy and phylogeny

''P. tobira'' is one of over 200 species of the genus ''Pittosporum'' which also includes ''kōhūhū'' and '' tarata''. Phylogenetic research suggests '' P. japonicum'' , '' P. glabratum'' , '' P. illicioides'', and '' P. balfouri'' are closely related.

Names and Etymology

The binomial qualifier ''tobira'' derives from the Japanese name for the plant. The genus name ''Pittosporum'' derives from the Greek substantives ' (meaning "pitch") and (meaning "seed") in reference to the resinous substance that surrounds the seed.

In Japan and China, where it is native to, it is known as (トベラ in Japanese) and (海桐花属 in Chinese). Its Japanese name, , comes from "" which roughly translates to "door tree". This is because the plant emits a foul odour when leaves or branches are cut and so it was hung up in doorways during Setsubun along with the heads of sardines.

In English, it is known as Japanese pittosporum, mock orange, Australian-laurel, and Japanese cheesewood. In German it is also known as ("Chinese sticky seed") or (Pech = pitch,tar, Same = seed). In Swedish it is called ("glossy shrubs"). In Brazilian Portuguese, it is known as lágrima-sabéia ("teardrop"), pau-de-incenso ("incense stick"), or pitósporo-japonês.

Chemistry

Although not typically considered edible, the nutritional composition of ''P. tobira'' seeds have been analyzed. The seeds are mostly carbohydrates (71.3%) while their low fat content (5.6%) means it cannot be classified as an oily seed. The high ash content may suggest the presence of considerable amounts of inorganic nutrients in this plant.

The total phenolic content was 102.7 mg gallic acid equivalents per gram (GAE/g) while the total flavonoid content was 31.62 mg of catechin equivalent per gram dry weight basis (CAE/g DW).

An HPLC analysis revealed the presence of five phenolic acids with caffeic acid being the most numerous (38.57 mg/g). The next most common phenolic acids were ferulic acid (20.07 mg/g), p-coumaric acid (12.85 mg/g), cinnamic acid (5.14 mg/g), and gallic acid (1.03 mg/g). Nineteen components were found to makeup 89.5% of the total essential oil content with oxygenated sesquiterpenes being most present (57.5%) followed by sesquiterpene hydrocarbons (11.8%) and oxygenated monoterpenes (6.7%). Spathulenol was the most representative component (48.0%), followed by isospathulenol (5.8%), δ-Elemene (4.2%), λ-gurjunene (4.0%) and camphor (3.7%). Additionally, it was found that ''P. tobira'' seed essential oils exhibited important antioxidant activity.

Methanol extracts of ''P. tobira'' was found to control more than 90% development of rice blast, an important rice pathogen for commercial rice production, at 1,000 μg/ml.

Cultivation and uses

This shrub is a common, drought-tolerant and fairly hardy landscaping plant. Many cultivars have been developed, including dwarf forms and the popular 'Variegata', which has variegated leaves. It is used for hedges, living privacy screens, and indoor and outdoor planter boxes. The stems, leaves, and dried fruits are used in flower arrangements.

''P. tobira'' is suitable for a Mediterranean climate, but may be more sensitive than other common ornamental plants to drought-induced stress. In 2014, a study comparing the effects of drought stress of five common ornamental plants found ''P. tobira'' to be the only plant whose total dry biomass was significantly affected (noting a 19% decrease in biomass). The plant may also be useful for fire-resistant landscaping due to its high gross heat of combustion. This plant may also be associated with more damage to other plant species when it is nonnative. A 2016 analysis of 49 plant species in green spaces in Madrid found ''P. tobira'' to be among the most likely shrubs to be associated with damage to native plant species.

The species and the cultivar 'Variegatum' have both gained the Royal Horticultural Society's Award of Garden Merit.

Ecology and interactions

Common pests of this plant include various aphids, mites, and leafhoppers, the cotton cushiony scale (''Icerya purchasi''), and root-knot nematodes (''Meloidogyne'' spp.). It can be attacked by the pit-making pittosporum scale (''Planchonia arabidis''). It is vulnerable to the fungal plant pathogen '' Erythricium salmonicolor'', which causes galls and the dieback disease known as pink limb blight.

The pathogenic plant fungus ''Rhizoctonia solani'' forms white, web-like basidial fructifications on the lower sides of infected leaves of Pittosporum tobira.

The fruit of the plant are not poisonous but not edible. However, they are eaten by bulbuls and other birds in Japan. The sticky substance around the seeds allow them to stick to the beaks of birds and be carried long distances. The stench given off when broken is thought to have evolved to repel predation from foraging animals but it is a favorite of the silka deer.

Gallery

File:Japanese Cheesewood -- Pittosporum tobira.jpg, Japanese Cheesewood flowers
File:Pittosporum tobira MHNT.BOT.2006.0.1264.JPG, ''Pittosporum tobira'' - MHNT
File:Pittosporum tobira Fruits.jpg, Fruits and seeds in Japan
File:Unidentified plants in Italy.JPG, ''P. tobira'' growing in Italy

References

External links

Jepson Manual TreatmentPhoto galleryFlora of ChinaFlowerDB

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tobira
Flora of China
Flora of Japan
Flora of Korea
Flora of Taiwan
Garden plants of Asia