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, synonym Platanus × acerifolia) 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. 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. It was first recorded in London around 1645.
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 symptomless P. orientalis of Turkish origin with two susceptible American sycamores (P. occidentalis). Progeny from these crosses were evaluated following several years of exposure to Apiognomonia veneta Hohn. ( = Gnomonia platani) anthracnose infection in the field. Four clones that remained symptom free were further evaluated for growth and landscape attributes in field and street plantings for 12 years. Two selections, both strong compartmentalizers, 'Columbia' and 'Liberty' were released August, 1984. [1 & 4].
Cultivars/Varieties
'Bloodgood', This is a popular selection and one of the first cultivars to be selected for anthracnose resistance, though reports vary regarding this trait. It is a large, rounded tree to 60' tall 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, which may limit its use in urban environments [3].
'Columbia', A tough plant that resists mildew and anthracnose, this pyramidal selection reaches 50' tall and features deeply-lobed, dark green leaves [3].
'Liberty', A U.S. National Arboretum introduction, this pyramidal grower reaches 50' and grows vigorously. It shows good tolerance for mildew, anthracnose, heat and drought [3].
'Metzam' (Metroshade™), A new introduction that grows very strongly to 70' tall with a pyramidal habit, this cultivar is also notable for its disease resistance and handsome lustrous green foliage that emerges with a reddish cast [3].
'Mirkovec', A very unusual selection out of Europe, this plant has a dwarf, shrubby habit and unusual variegated lobed leaves with pink, cream and bronze regions. It is not commonly available [3].
‘Suttneri’, Leaves marked creamy white. 70’ tall x 50’ wide [5].
`Yarwood’, Very resistant to powdery mildew and fairly resistant to anthracnose [2].
It is a large deciduous tree growing to 20-35 m (exceptionally 43 m) tall, with a trunk up to 3 m diameter. The bark is usually smooth and exfoliating, pale grey-green, rarely thicker, scaly, and buff-brown, not exfoliating. The leaves are alternate, 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.
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.
[edit] Ecology
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 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 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 tree also drops many sticks and branches during storms, and 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, 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.
[edit] References
- Huxley, A., ed. (1992). New RHS Dictionary of Gardening. Macmillan.
- Rushforth, K. (1999). Trees of Britain and Europe. HarperCollins ISBN 0002200139.
- [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 0-7894-1934-2.
