The London plane tree (Platanus × acerifolia) is a very large deciduous tree that is quite resilient in urban conditions. This tree is a cross between two sycamore species: Platanus occidentalis (American sycamore) and Platanus orientalis (Oriental plane).
This very large tree with maple-like leaves can be hard to distinguish from the American sycamore since it has the same mottled brownish-green or grayish-green bark and grows to roughly the same size—75 to 100 feet with a spread of 60 to 75 feet. However, the lobes on the leaves of the London plane tree are deeper than with the American sycamore, and this is the species most often planted in urban environments. The American sycamore more often appears in native situations, growing along streams and in lowlands.
Like all sycamores, the London plane has bark that peels away in irregular patches to show creamy whitish-green inner bark. The large leaves have three to five lobes and are 4 to 9 inches wide. Fall foliage is a rather plain yellow-brown. Small flowers appear in clusters in May, gradually ripening into small fruiting balls that turn brown in fall.
The London plane tree is a hybrid plant, a cross between the American sycamore (Platanus occidentalis) and the Oriental plane tree (Platanus orientalis). Platanus is the sole genus found in the Platanaceae plant family. Occasionally, especially in older literature, this tree may be called Platanus x hispanica or Platanus hybrida.
Hybridization is thought to have occurred accidentally in either Spain or London when the American sycamore and Oriental plane tree were planted close to one another. The hybrid was recognized and cataloged in 1789 by Scottish botanist William Aiton.
London plane tree is used most often in urban landscapes where a very large tree is desired. It has excellent tolerance for city pollution and is a common choice in large city parks and other public lands. It also works well in boulevards and planting strips because the roots can tolerate small spaces with soil compaction is an issue. The roots may also cause damage to buildings, sidewalks, and driveways, so choose your location wisely. Its huge size and messy growth habit make the London plane tree unsuitable for all but the largest residential landscapes. The short stiff hairs and falling seeds can create a nuisance, as well as an irritant for people suffering from allergies.
The London plane tree is very easy to grow in any average, medium-to-wet soil. It thrives in rich, humusy soils that are constantly moist. It can handle alkaline pH levels. London plane tree prefers full sun but will tolerate light shade, and it is quite tolerant of urban pollution.
Left unpruned, this specimen will grow very large, but it is often trained with a technique called pollarding, in which the tree is pruned to maintain short, club-like branches. To keep this unique shape, annual pruning is necessary. Another pruning style that is used with this species is pleaching, in which the branches are braided together to form a living fence.
Propagation is carried out through cuttings or from the seeds that break off from the fruit ball in the fall and spread through the air. Grafting is used to preserve the traits of cultivated varieties.
- 'Liberty' is a U.S. National Arboretum introduction, a quick-growing variety with a pyramidal shape. It has a good tolerance for mildew, anthracnose, heat, and drought.
- 'Columbia' resists mildew and anthracnose, and has dark green leaves.
- 'Metzam' (Metroshade) is a fast-growing variety with a pyramid shape. Another disease-resistant cultivar, this one has leaves that emerge with a reddish color that quickly become a lustrous green.
- 'Mirkovec' is a dwarf variety with a shrubby growth habit and unusual variegated lobed leaves with pink, cream, and bronze colors.
London planetree may be susceptible to the same sycamore anthracnose disease that affects the American sycamore, but there are disease-resistant cultivars available, including 'Columbia' and 'Liberty.' Another disease affecting this tree is canker stain, which can be fatal. Canker, leaf spot, and powdery mildew are also seen in London plane tree.
Insect pests include borers, scale, sycamore lace-bug, Japanese beetles, caterpillars, and mites.