Platanus x hispanica
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| London Plane | ||||||||||||||
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 London Plane seed ball
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| Platanus × hispanica Muenchh. |
The London Plane or Hybrid Plane (Platanus × hispanica, synonyms Platanus × acerifolia and Platanus × hybrida) is a tree in the genus Platanus. It is usually thought to be a hybrid of the Oriental Plane, P. orientalis, with the American Plane (American sycamore), P. occidentalis. Some authorities think that it may be a cultivar of P. orientalis, but there is little evidence for this.
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[edit] Description
It is a large deciduous tree growing to 20-35 m (exceptionally over 40 m) tall, with a trunk up to 3 m or more in circumference. The bark is usually pale grey-green, smooth and exfoliating, or buff-brown and not exfoliating. The leaves are thick and stiff-textured, broad, palmately lobed, superficially maple-like, the leaf blade 10-20 cm long and 12-25 cm broad, with a petiole 3-10 cm 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 spherical inflorescences on a pendulous stem, with male and female flowers on separate stems. The fruit matures in about 6 months, to 2-3 cm diameter, and comprises a dense spherical cluster of achenes with numerous stiff hairs which aid wind dispersal; the cluster breaks up slowly over the winter to release the numerous 2-3 mm seeds.
[edit] Origin
It was first recorded as occurring in Spain in the 17th century, where the Oriental Plane and the American Plane had been planted in proximity to one another.
The leaf and flower characteristics are intermediate between the two parent species, the leaf being more deeply lobed than P. occidentalis but less so than P. orientalis, and the seed balls typically two per stem (one in P. occidentalis, 3-6 in P. orientalis). The hybrid is fertile, and seedlings are occasionally found near mature trees.
Controlled reciprocal pollinations between Platanus occidentalis and P. orientalis resulted in good yields of germinable seed and true hybrid seedlings. Crosses of both species, as females, with P. racemosa and P. 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 in P. orientalis [1].
In 1968 and 1970, Frank S. Santamour, Jr., recreated the P. orientalis, P. occidentalis cross using a P. orientalis of Turkish origin with American sycamores (P. occidentalis). The offspring were evaluated following several years of exposure to anthracnose infection. Two selections'Columbia' and 'Liberty' were released in August, 1984. [1 & 4].
[edit] Cultivars and varieties
- Augustine Henry. This is a tall growing variety, with very large, pale green leaves. It produces a strong leader and a cylindrical trunk. (Bean)
- Bloodgood, This is one of the first cultivars to be selected for anthracnose resistance. It is a rounded tree with deep green leaves that turn a poor yellow in fall. The plant tolerates poor cultural conditions, including heat, drought and poor soil. Recent observations indicate susceptibility to ozone.
- Columbia. Resists mildew and anthracnose, this tree has deeply-lobed, dark green leaves [3].
- Liberty. A U.S. National Arboretum introduction, this pyramidal tree grows vigorously. It shows good tolerance for mildew, anthracnose, heat and drought [3].
- Metzam (Metroshade), A new introduction that grows strongly with a pyramidal habit, this cultivar is also said to be disease resistant with lustrous green foliage that emerges with a reddish cast [3].
- Mirkovec. Has a dwarf, shrubby habit and unusual variegated lobed leaves with pink, cream and bronze regions. [3].
- Pyramidalis. A cultivar or cultivar group common in London, with rich glossy green leaves, and a characteristic tendency to produce straight branches, compared to sinuous branches ones in other forms. (Bean)
- Suttneri. Leaves are variegated creamy white. [5].
- Yarwood. Very resistant to powdery mildew and fairly resistant to anthracnose [2].
[edit] Usage
It is very tolerant of atmospheric pollution and root compaction, and for this reason it is a popular urban roadside tree. 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, not just London but Buenos Aires, New York City, Paris, Madrid, Melbourne,Shanghai, Chicago and many others. It has a greater degree of winter cold tolerance than the Oriental Plane, and is less susceptible to anthracnose disease than the American Plane. The seeds are used as a food source by some finches and squirrels.
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. The large leaves can create a disposal problem in cities. These leaves are tough and sometimes can take more than one year to break down if they remain whole.
The leaf of the London Plane is the symbol of the New York City Department of Parks and Recreation[1], and is prominently featured on signs and buildings in public parks across the city. Ironically the tree is today on the NYC Parks Department's list of restricted use trees for street tree planting.
London Planes are often pruned by a technique called pollarding. 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.
[edit] References
- Bean. Trees and Shrubs hardy in the British Isles. (8th ed., 1976)
- Huxley, A., ed. (1992). New RHS Dictionary of Gardening. Macmillan.
- Rushforth, K. (1999). Trees of Britain and Europe. Harper Collins ISBN 0-00-220013-9.
- [1] Interspecific Hybridization in Platanus. Author: Santamour, Frank S.1. Source: Forest Science, Volume 18, Number 3, 1 September 1972, pp. 236–239(4) Publisher: Society of American Foresters
- [2] Trees for you. http://www.treesforyou.org/Selection/Articles/sycamores.htm
- [3] University of Connecticut. http://www.hort.uconn.edu/Plants/p/plaace/plaace1.html
- [4] Nov. 1999 U.S. National Arboretum Plant Introduction (platanus PDF), Floral and Nursery Plants Research Unit. U.S. National Arboretum: www.ars-grin.gov/na/
- [5] The American Horticultural Society A-Z Encyclopedia of Garden Plants, pg. 808. DK Publishing, www.dk.com , 1st edition 1997, ISBN 0789419432.
