The London plane thrives in cities, though its relatives prefer riverbanks
Most plane trees grow wild along rivers and in wetlands, yet one hybrid, the London plane, has turned out to be remarkably tough in cities. It lines streets in London and across the temperate world. Its patchwork bark, peeling away in irregular flakes, gives mature trunks their familiar mottled look.
Platanus is a small genus, the only surviving group in its family. Mature trees reach 30 to 50 metres, and all but one species, P. kerrii, shed their leaves each year. The type species is the Oriental plane. Though wetland plants by nature, planes have proved drought-tolerant in cultivation. In English they are planes or plane trees, and some North American species, especially Platanus occidentalis, are called sycamores, a name also applied to several unrelated trees. The word plane came through Old French from Latin platanus and ultimately from a root meaning broad and flat, a reference to the wide leaves.
A neat detail hides in the leaf stalk. Its base swells and wraps completely around the young bud beside it, so that bud only becomes visible once the leaf falls. The flowers are tiny and packed into round heads, male and female on the same tree, and are pollinated by wind. How many heads a cluster carries helps identify the species.
After pollination, each female head becomes a ball 2.5 to 4 centimetres across, holding several hundred small single-seeded fruits. Each fruit is cone-shaped, pointing inward, and carries a tuft of stiff yellow-green bristles at its base that help it catch the wind, much as a dandelion seed does. Beneath the surface lies a core about a centimetre wide wrapped in a fine peelable mesh.
Genetics has redrawn the family tree. DNA shows that a group of western North American planes is more closely related to the Eurasian Oriental plane than to the planes of eastern North America. The two lineages have nonetheless swapped genes through hybridisation, and studies in Mexico have added more recognised species.
Source: Platanus
