In the early to mid 1600s, botanists grew the American sycamore and Oriental planetree close to one another at the well-known Oxford Botanical Gardens in England. Apparently, these two species spontaneously hybridized in the late 1600s and produced a new hybrid species, the London planetree (Platanus X hybrida, but also given other Latin names). Although Platanus occidentalis and Platanus orientalis are believed to have been separate species for at least 50 million years, their hybrid was fertile and produced its own seeds.
The London planetree combines some of the characteristics of each of its parent species, as is typical of hybrid species. The leaves of the American sycamore have shallow lobes, the leaves of the Oriental planetree have deep lobes, and the leaves of the London planetree have lobes with intermediate depth. One fruit cluster is borne on each peduncle in the American sycamore, several fruit clusters are borne on each fruit cluster of the Oriental planetree, and two (or occasionally three) fruit clusters are borne on each peduncle of the London planetree.
Like the American sycamore, but unlike the Oriental planetree, the London planetree can endure cold climates. The London planetree can endure pollution and other environmental stresses better than either species. Thus, it is often cultivated as an ornamental tree and planted along streets in America and Britain. Moreover, the London planetree can grow up to 3 ft (0.9 m) per year, making it a very popular shade tree for homeowners.
In the 1920s, more than 60% of the trees planted along the streets of London were London planetrees. They are also well known in the Kensington Gardens of London.
Heywood, V.H. Flowering Plants of the World. Oxford: Oxford University Press, 1993.
White, John, and David More. Illustrated Encyclopedia of Trees. Portland, OR: Timber Press, 2001.
Peter A. Ensminger