The London plane tree (Platanus acerifolia) is a hardy ornamental tree in Manhattan, Kansas. This tree is a hybrid of the oriental plane tree (Platanus orientalis) and the American sycamore (Platanus occidentalis). The original hybridization event might have occurred in about 1650 in the Tradescant nursery garden in London. The basis for this conjecture is merely the recorded presence of the parental species in the nursery garden, however. The hybridization event could have occurred anyplace in Europe that had ornamental specimens of the American sycamore and either ornamental specimens or native specimens of the oriental plane tree.
There are several different hypotheses about the origin of the London plane tree, and some people don't believe that it's really a hybrid between the oriental plane tree and the American sycamore. These species do hybridize, however, producing offspring that are extremely similar to the London plane tree, and molecular techniques will probably be used some day to firmly prove or disprove the hybrid origin of the London plane tree.
The London plane tree is usually propagated asexually. The first cuttings from the hybrid were probably rooted and planted in London in about 1680. So far, none of the trees in London have become decrepit from old age. Based on the longevity of the oriental plane tree and the American sycamore, hybrid specimens may not begin to become decrepit until they have reached 500 years of age. Gradually, more and more specimens of the hybrid were planted in London until they accounted for over 60% of the trees in the 1920's. Part of the reason for its popularity was its ability to withstand severe pollution from the industrial revolution. The smooth surfaces of its leaves were well cleaned by rain and the outer layers of the tree's bark fell away in patches, shedding pollutants. It was also tolerant of heat reflected from the streets and was more tolerant of cold winters than the oriental plane tree.
A large proportion of the seed from this tree is not viable. This is fantastic news for people who are concerned about competition between non-native and native trees. This tree can successfully cross with the oriental plane, producing forms that can gradually merge into the typical form of the oriental plane tree. I haven't found any information about its ability to cross with the American sycamore. However, I suspect that experts who recommend the London plane tree for planting in our cities may be right, and there is little chance that this non-native tree will influence the survival of our native trees. Now, having arrived at that opinion, I will be able to enjoy the specimens of this tree that much more.
In the future, as I walk past King Hall at Kansas State University, I will notice that the specimens of the London plane tree near Mid Campus Drive are similar in appearance to specimens of the American sycamore, but usually have more than one fruit per stem and have lobes in their leaves that are not much wider than they are long. I will gaze up at these large, beautiful specimens and wonder how much larger they will be when they reach 500 years of age.
© - 2003 Thomas Morgan