Platanus occidentalis L.

Platanus occidentalis is a characteristic species of the forests which once dominated the river valleys across much of the eastern third of North America, extending from central Texas to the far south of Canada’s Ontario Province. The secondary forests which have regrown widely in this region remain rich in tree species and the plane-trees tend to occur singly or in small groups, although in the bottomlands of Mississippi pure stands up to 40 ha in extent are known (Wells & Schmidtling 1990). They can tolerate winter flooding, but die if inundated for more than a fortnight during the growing season; within the region’s iconic Taxodium distichum and Nyssa aquatica swamplands, they are confined to patches of higher ground (Silberhorn 1994).

The rich valley bottom sites which Platanus occidentalis favoured were among the first areas of woodland to be cleared for agriculture by European settlers, meaning that, in the case of trees as long-lived as planes, the largest in the wild today are scattered survivors in remote and generally sub-optimal habitats, such that this tree’s potentially vast stature is liable to be underestimated. Elwes & Henry (1906–1913) cited the experience of the ornithologist Robert Ridgway, who in the 1880s recalled finding near his birthplace at Mount Carmel, Illinois, a fallen trunk 5.8 m thick at the base and nearly 6 m thick 6 m up, where it forked into three huge limbs each over 20 m long. However this tree was measured, it must have been very much larger than any tree of any species measured more recently in the eastern United States, according to the records provided by American Forests 2024. Because the heartwood rots with age, the lifespan of many old P. occidentalis cannot be calculated from their growth rings; American Forests (2025) suggests a top age of 412 years, but the analogy of the estimated 2000-year potential lifespan for European P. orientalis might imply that this figure underestimates the likely ages of specimens such as Ridgway’s fallen giant.

The original forests of the eastern United States seem to have tended more towards closed-canopy woodland than was the case for equivalent ecosystems in temperate Europe; fire, which in pre-Columbian times took the place of Europe’s large primeval herbivores in creating a patchwork of grassy clearings, will have had less impact on the moist, riverine habitats where plane-trees naturally grow (Wikipedia 2025). Platanus occidentalis is certainly more of a woodland tree than P. orientalis, one consequence of this being that it is less well adapted to harsh urban conditions than its hybrid descendent P. × hispanica; sensitivity to ozone in the lower atmosphere seems a particular problem (Kline et al. 2008; Jacobson 1996). Young trees, used to side shelter and competition, are often much more slender than is the norm for Oriental and London Planes; one from the collection CAHY 10–92 for example, planted in woodland shelter at Wakehurst Place in England, was 17 m tall after 30 years’ growth, with a trunk only 14 cm thick, placing it within the very select group of trees – as opposed to saplings – whose height is more than a hundred times their dbh (Tree Register 2025). Even within its native area, P. occidentalis is very little utilised as a ornamental tree, with its hybrids enjoying a monopoly as formal and street plantings.

The vigorous performance of the Wakehurst Place tree so far is at odds with the reputation which Platanus occidentalis has acquired in cultivation in northern Europe. In W.J. Bean’s experience at Kew through the first half of the 20th century, the species was a comprehensive failure, failing to ripen its new growths before autumn frosts cut them back and hence never reaching tree size. These failures seem to have coloured expectations across Europe, even where summers are much longer and warmer than those of London; when France’s London Planes started dying of Canker Stain Disease (CSD), the potential of the naturally resistant P. occidentalis as a replacement tree was generally overlooked, thanks to the view that ‘this species is not adapted to the climatic conditions in Europe’ (Vigouroux & Olivier 2004).

In fact there are plenty of records for the successful performance of Platanus occidentalis across much of Europe. The species first seems to have been cultivated by John Tradescant at his garden, ‘The Ark’, at Lambeth, now in south London, around 1630 (Gerard & Johnson 1633), probably as material from the English colony in Virginia. Since plane trees apparently of hybrid origin were being documented in England after just a few decades, the implication is that that Tradescant’s trees and their progeny or sister plants had at least grown well enough to flower and fruit. In the later 18th century, Samuel Goodenough, Bishop of Carlisle and amateur botanist, had been able to collect a specimen of P. occidentalis with a mature fruit-ball, almost certainly from Kew (Bean 1976). During the later 20th century, P. occidentalis was again growing well in London; one of a pair outstationed by Kew Gardens at nearby Bushy House in 1952 was a respectable 23 m × 78 cm dbh by 2016, while in the slightly cooler climate of Westonbirt National Arboretum in Gloucestershire, one accessioned as recently as 1985 was 19.5 m tall by 2024. As far north as the Royal Botanic Garden Edinburgh, 1936 and 1946 accessions had made good trees 19 m and 18 m tall in 2015 (Tree Register 2025). Summers in Edinburgh, in 2025, remain significantly cooler and shorter than were those at Kew even during the ‘Little Ice Age’, making it seem likely that the difficulties Bean experienced in growing P. occidentalis in London a century ago owed as much to the city’s then extremely polluted air as they did to its moderately maritime climate; in the case of a species with the broad natural range of P. occidentalis, provenance must also be important.

One factor which has served to obscure the story of the performance of Platanus occidentalis across Europe has been the long-term failure of botanists and gardeners to distinguish the true species from its hybrid offspring. In the 1830s, for example, J.C. Loudon described many thriving trees in Britain and Ireland as P. occidentalis (Loudon 1838); nowadays these are all assumed to have represented early plantings of P. × hispanica, although it is not beyond the bounds of reason that some of them could have been genuine. In continental Europe, this confusion continues to the present day, with many huge and historic trees being labelled or described as P. occidentalis. The records posted at Monumental Trees (2025) often allow positive identification through expert scrutiny and, although by 2025 many of these trees had been confidently re-identified within that resource as P. × hispanica, several do seem likely to represent genuine P. occidentalis. Among these are a tree at Presov in Slovakia, 32 m × 2.48 m dbh (planted after 1870 in a very rich soil), one c. 33 m × 2.27 m dbh at Schloss Trumau in Austria, and one 1.94 m dbh at le Manoir de Bigards in northern France. (Genuine P. occidentalis is supposed to have been introduced to France by Georges-Louis Leclerc, the Comte de Buffon, in the mid 18th century – Geerinck 1998). Although these giants grow in kindly conditions on large estates, rather than in tough urban situations, they certainly do not suggest a species which struggles in the climate of central Europe. Today, P. occidentalis is successfully cultivated as far north as the Linnaean Garden of Uppsala University in Sweden (Royal Botanic Garden Edinburgh 2025).

Although the sizes of some of these European trees bear comparison with the best specimens of Platanus × hispanica and of P. orientalis, P. occidentalis should not be considered as an equal substitute. Leaving aside the issue of its susceptibility to urban pollutants and its relative discomfort in growing solo rather than as a part of a woodland community, it is highly susceptible to Plane Anthracnose, a fungal infection which is endemic to Europe and to which P. orientalis has a good degree of resistance. Anthracnose will not kill a plane-tree unless it is already severely weakened, but in warm and humid springs specimens of P. occidentalis can be completely defoliated and will take time to grow a new crop of leaves – something which obviously affects their value as ornamental plants or as shade trees. (For a further discussion of the pests and diseases of Platanus, see the genus article.) The leaves, being only shallowly lobed, may also be felt to be less attractive than the deeply cut foliage of P. orientalis and of some of its hybrids. The growth form of P. occidentalis is variable, but seldom approaches the magnificent shapeliness of the best hybrid clones.

Genuine Platanus occidentalis can only be distinguished from look-alike forms of the hybrids by studying the fruit-balls. It is unusual for P. × hispanica to carry these singly, as the American parent usually does; the balls of the hybrid have a spikier look, since the top of each individual fruit (achene) is pointed or rounded rather than flattened, and is usually tipped until winter with a persistent style which projects about 5–7 mm; in P. occidentalis the style is more quickly shed, leaving just a 1 mm stub. The very shallowly lobed and almost rounded leaves of many P. occidentalis are also distinctive; the young foliage is slightly hairier, and these hairs take rather longer to wear off.

In the south-eastern United States, Platanus occidentalis has found one use as a fast-growing biomass crop (Wells & Schmidtling 1990), although in these monocultures anthracnose can be a particular problem. Plantations are also sometimes made for the species’ timber, which is strong, odourless and takes a good polish, and is used for furniture, veneers, musical instruments, and chopping boards (Paratley 2025). Native Americans used to drink the tree’s sugary sap (Chengappa 2022).

In some nomenclatural systems, the range of Platanus occidentalis extends southwards from central Texas into northeastern Mexico (Coahuila) as the variety glabrata (Fernald) Sarg., or the variety palmeri (Kuntze) Nixon & Poole ex Geerinck. These populations differ obviously from the plane-trees of central and southern Mexico in their much less hairy leaves which consequently do not look silvered underneath, but their leaves’ often untoothed lobes are one featured shared with P. mexicana and P. rzedowskii rather than with P. occidentalis; they seem to form part of a cline, with features such as leaves with untoothed lobes occuring within the populations of ‘good’ P. occidentalis from Oklahoma, Iowa, Arkansas and Louisiana, and even rarely further east (Nixon & Poole 2003; Grimm & Denk 2010). For simplicity’s sake alone, the core population is discussed further here as the species P. glabrata.