Platanus

Lore & Background

The flowers of Platanus are reduced and borne in globose heads, with male and female flowers separate but on the same plant. The fruit is an aggregate ball of achenes, each with a tuft of bristles aiding wind dispersal. The leaves are simple and alternate, with the petiole base wrapping around the young bud. Mature bark peels in irregular patches, creating a mottled appearance. Phylogenetic studies divide the genus into two subgenera: Castaneophyllum (containing P. kerrii) and Platanus (all others). Within subgenus Platanus, genetic evidence reveals two distinct lineages: the Atlantic North American (ANA) clade and the Pacific North American-European (PNA-E) clade. Hybridization and introgression have occurred between these lineages, as seen in species like P. rzedowskii and the hybrid London plane (Platanus × hispanica). The fossil record of Platanus leaves and fruit begins in the Paleocene. Despite geographic separation, North American and Old World species can cross to produce fertile hybrids, such as the London plane, which is an anthropogenic hybrid between P. occidentalis and P. orientalis.

Reader's Guide

Platanus trees are significant for their ecological and urban roles. They are often found in riparian or wetland habitats in the wild, but many species prove drought-tolerant in cultivation. The hybrid London plane (Platanus × hispanica) is especially valued for its tolerance of urban conditions and has been widely planted in London and elsewhere. The genus illustrates the concept of a 'Coral of Life,' where modern species result from both evolutionary splitting and hybridization. Platanus species are susceptible to several diseases, including plane anthracnose and Ceratocystis platani wilt. The North American species are mostly resistant to the wilt disease, while Old World species are highly sensitive. In the 21st century, Massaria disease, caused by Splanchnonema platani, has attacked plane trees across Europe. Human exposure to fine star-shaped trichomes from Platanus trees can cause 'platanus cough,' with symptoms of shortness of breath, coughing, and irritated eyes. This is not an allergic reaction but direct irritation, and protection involves avoiding contact and wearing protective glasses and masks.

Did You Know?

• The genus name Platanus comes from Ancient Greek πλάτανος, which referred to Platanus orientalis.
• The hybrid London plane (Platanus × hispanica) is an anthropogenic hybrid between North American P. occidentalis and Mediterranean P. orientalis.
• The fruit ball of Platanus is 2.5–4 cm in diameter and contains several hundred achenes, each with a tuft of bristles for wind dispersion.
• Platanus trees can cause 'platanus cough' due to fine star-shaped trichomes that break off in strong wind after a dry period.