| London plane | |
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| London plane trees inBerkeley Square, London, planted 1789 | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Order: | Proteales |
| Family: | Platanaceae |
| Genus: | Platanus |
| Species: | P. × hispanica |
| Binomial name | |
| Platanus× hispanica | |
| Synonyms[1] | |
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TheLondon plane, or sometimeshybrid plane,Platanus × hispanica,[2] is a tree in the genusPlatanus. It is often known by thesynonymPlatanus ×acerifolia, a later name. It is ahybrid ofPlatanus orientalis (oriental plane) andPlatanus occidentalis (American sycamore).
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The London plane is a largedeciduous tree growing 20–40 m (65–130 ft), exceptionally to 50 m (160 ft) tall, with a trunk up to 10 m (33 ft) in circumference.[3] Thebark is usually pale grey-green, smooth and exfoliating, or buff-brown and not exfoliating. Theleaves are thick and stiff-textured, broad, palmately lobed, superficiallymaple-like, the leaf blade 10–20 cm (4–8 in) long and 12–25 cm (5–10 in) broad, with apetiole 3–10 cm (1–4 in) long. The young leaves in spring are coated with minute, fine, stiff hairs at first, but these wear off and by late summer the leaves are hairless or nearly so. The flowers are borne in one to three (most often two) dense sphericalinflorescences on a pendulous stem, with male and female flowers on separate stems (monoecy). The fruit matures in about 6 months, to 2–3 centimetres (0.8–1.2 in) diameter, and comprises a dense spherical cluster ofachenes with numerous stiff hairs which aid wind dispersal; the cluster breaks up slowly over the winter to release the numerous 2–3 mm (0.08–0.12 in) seeds. The London Plane is one of the most efficient trees in removing small particulate pollutants in urban areas.[4]
It shares many visual similarities withAmerican sycamore (Platanus occidentalis), from which it is derived; however, the two species are relatively easy to distinguish, considering the London plane is almost exclusively planted in urban habitats, while American sycamore is most commonly found growing in lowlands and alluvial soils along streams.[5]
The species was formed by hybridization in the 17th century afterP. orientalis andP. occidentalis had been planted in proximity to one another. It is most likely that the hybridization took place in Spain or southern France, as theP. occidentalis parent needs considerable summer heat to grow well and is near-impossible to grow successfully in cooler climates like Britain,[6] but there is also speculation that it could have happened inVauxhall Gardens in London whereJohn Tradescant the Younger saw the tree in the mid-17th century.[7][8]The leaf and flower characteristics are intermediate between the two parent species, the leaf being more deeply lobed thanP. occidentalis but less so thanP. orientalis, and the seed balls typically two per stem (one inP. occidentalis, 3–6 inP. orientalis). The hybrid is fertile, and seedlings are occasionally found near mature trees.
Controlled reciprocal pollinations betweenP. occidentalis andP. orientalis resulted in good yields of germinable seed and true hybrid seedlings. Crosses of both species, as females, withP. racemosa andP. wrightii produced extremely low yields of germinable seed, but true hybrids were obtained from all interspecific combinations. Apomixis (asexual reproduction from non-fertilized seeds) appeared common inP. orientalis.[9]
In 1968 and 1970, Frank S. Santamour Jr. recreated theP. orientalis byP. occidentalis cross using aP. orientalis of Turkish origin with American sycamores (P. occidentalis). The offspring were evaluated following several years of exposure toanthracnose infection. Two selections, 'Columbia' and 'Liberty', were released in August 1984.[9][10]
Platanus × hispanica was first formally described in the botanical literature by the German botanistOtto von Münchhausen in his 1770 workder Hausvater.[11] Later, it was described in the botanical literature by the Scottish botanistWilliam Aiton in his 1789 workHortus Kewensis as avariety ofP. orientalis.[12] Aiton described this variety with a two-word Latin diagnosis, "foliis transversis", and called it the Spanish plane tree.[13] In 1805,Carl Ludwig Willdenow chose to elevate Aiton's variety to species rank, publishing the new speciesP. acerifolia in the fourth edition ofSpecies Plantarum.[14][15] The species name was then modified to include the multiplication symbol to indicate its suspected hybrid parentage.
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| Avenue of London plane trees onJesus Green | |||
Two of 50 "Great British Trees" thatthe Tree Council selected in 2002 in honour ofQueen Elizabeth II's Golden Jubilee are London planes.[16] The list specifically mentions Britain's first London plane being in the city ofEly, Cambridgeshire.
The London plane is very tolerant of atmospheric pollution and root compaction, and for this reason it is a popular urban roadside tree. It was planted extensively inVictorian times to weather the pollution of London. It is now extensively cultivated in most temperate latitudes as an ornamental and parkland tree, and is a commonly planted tree in cities throughout the temperate regions of the world, in London and many other cities.[7] It has a greater degree of winter cold tolerance thanP. orientalis, and is less susceptible toanthracnose disease thanP. occidentalis. The tree has gained theRoyal Horticultural Society of Great Britain'sAward of Garden Merit.[17][18]
The tree is fairly wind-resistant. However, it has a number of problems in urban use, most notably the short, stiff hairs shed by the young leaves and the dispersing seeds; these are an irritant if breathed in, and can exacerbate breathing difficulties for people with asthma.[6] The vigorous roots can also cause problems with paving in cities, making uneven surfaces with tripping hazards.[6] The large leaves can create a disposal problem in cities, as they are tough and sometimes can take more than one year to break down if they remain whole.
London planes are often pruned by a technique calledpollarding. A pollarded tree has a drastically different appearance than an unpruned tree, being much shorter with stunted, club-like branches. Although pollarding requires frequent maintenance (the trees must usually be repruned every year), it creates a distinctive shape that is often sought after in plazas, main streets, and other urban areas.
According to theNew York City Department of Parks and Recreation the symbol of that organization is a cross between the leaf of the London plane and a maple leaf. It is prominently featured on signs and buildings in public parks across the city. The tree is on the NYC Parks Department's list of restricted use species for streettree planting, because it constitutes more than 10% of all street trees.
In Australia, the London plane is used extensively as a street tree in major cities, particularlySydney,Melbourne,Adelaide andPerth. The tree is commonly used because of its resilience to warm weather, its benefits as ashade tree, resistance to breakage and tolerance of urban pollution.
InJohannesburg, South Africa many London planes line streets in older suburbs. In recent years the trees have been infested with the Polyphagous shot hole borer beetle (Euwallacea fornicatus). Some trees are reportedly developing resistance mechanisms but there are currently no effective measures against the borer beetle and it remains unclear how many trees will have to be cut down.[19]
The London plane is cultivated in central, northeastern and southern China.[12]
Whenquarter-sawn, the timber has a distinctive and highly decorative appearance of dark reddish-brown flecks against a lighter background and is known aslacewood.[20]
