Platanus racemosa Nutt.

Platanus racemosa is the characteristic plane or sycamore species of central and southern California, growing near streams and rivers and forming picturesque, wide-spreading and often strikingly white-barked trees; occasionally, their autumn colour can be a deep gold. A specimen growing before 1884 in Santigo Canyon, Los Angeles County, had a recorded dbh of 2.85 m (Jacobson 1996). The species commonly grows in open woodland alongside other trees, but dominates in one rare habitat type, Sycamore Alluvial Woodland, which occurs along the floors of mountain valleys surrounding California’s Central Valley in places where the soil is a deep alluvial gravel (Wikipedia 2025).

Especially in southern California, natural stands of Platanus racemosa are often retained for their shade and shelter in urban locations, and this has long been the preferred Platanus species for planting in the south-western States. Like the rest of its genus it is a thirsty tree, and will need plenty of irrigation if planted away from water or underground aquifers; in the right location, it is very drought tolerant (San Marcos Growers 2025).

The natural range of Platanus racemosa is entirely disjunct from that of P. occidentalis, and the Californian tree lacks the latter species’ innate resistance to Canker Stain Disease (CSD), a generally fatal disease of plane-trees. CSD was first identified in California in 1961 on street trees in Modesto, where it went on to attack P. racemosa and P. × hispanica equally (Perry & McCain 1988). In marked contrast to the spread of CSD across Europe, however, it has not become a significant problem in this area. Plane Anthracnose, a major issue in the eastern United States, has also had less impact in California, presumably because springs are seldom humid enough for the fungal spores to spread far. However, when visiting the Los Angeles area in 2023, which had had a very cool wet spring that year, John Grimshaw (pers. comm.) observed trees of P. racemosa that were almost defoliated by anthracnose (see image).

The poor performance of Platanus occidentalis from the eastern United States at Kew through the early 20th century has helped to give New World Platanus a reputation for being tender or a least difficult to grow in Europe and has probably deterred experimentation. P. californica is certainly a tree that enjoys plenty of warm sunshine and is unlikely to tolerate intense frost, and several early attempts to grow it in Britain met with failure (Bean 1976). The vigorous tree sold by the van Houtte nursery in Belgium as ‘P. californica’ to Kew in 1878 is a clone of London Plane (P. × hispanica), known today as ‘Augustine Henry’. However, a P. racemosa accessioned in 2015 at the Sir Harold Hillier Gardens in southern England was a respectable 4.6 m tall by 2022, while at Matthew Ellis’s Grange Farm Arboretum in the Lincolnshire Fens, where soils are extremely fertile and summers among the hottest in Britain, several young plants were up to 4 m tall in 2019 (Tree Register 2025).

Even within the native zone of Platanus racemosa, introduced London Planes have sometimes been planted in its stead. Evidence of hybridisation has been found along the Sacramento River in California, leading to concerns of genetic erosion within the native populations (Johnson et al. 2016). Some of the trees sold as P. racemosa in American nurseries may themselves be accidental hybrids with P. × hispanica; the now defunct San Marcos Growers in California preferred to sell scions of a genuine specimen of P. racemosa, the ‘Sister Witness Tree’ in Goleta, which antedated the introduction of P. × hispanica to the area (San Marcos Growers 2025).

Inland, and at higher elevations, Platanus racemosa is replaced by forms with somewhat less pubescent foliage and generally only about three seed-balls per inflorescence. In their definitive account of New World Platanus, Nixon & Poole (2003) follow a treatment recognising this taxon as a variety of P. racemosa (var. wrightii (S. Wats.) Benson), but admit that the choice of whether to treat is as a variety, a subspecies or a species remains, on macroscopic evidence, ‘somewhat arbitrary’. For the sake of simplicity, this account follows Plants of the World Online in treating this taxon as a species, P. wrightii S. Wats. (Royal Botanic Gardens Kew 2025).