A tree up to 140 ft high in N. America, with a bark similar to that of the London plane. Leaves shallowly lobed, sometimes very indistinctly so (but occasionally they are quite as deeply lobed as on some leaves of the London plane), lobes acuminate at the apex, usually sinuately toothed, 4 to 7 in. long and about as wide, cordate or truncate at the base or sometimes with a decurrent wedge each side of the junction with the petiole (as so often in the oriental and London planes), densely stellate-tomentose when young, at length glabrous except for some down remaining on the midrib and veins beneath (but the original coating persists longer than in the oriental and London planes); petioles 3 to 5 in. long; stipules 1 to 11⁄2 in. long, entire or toothed. Fruit clusters solitary (rarely in twos), on glabrous peduncles 3 to 6 in. long; achenes truncate to rounded at the apex, crowned by the short persistent base of the style and ringed only at the base with a tuft of hairs (in the oriental plane the achenes are rather more conical at the apex and sometimes the body of the achene is hairy; a more reliable difference is that in the oriental plane, and most of the hybrids, the peristent style is longer and the fruit-balls hence more bristly than in the American species).
Native of eastern and southern N. America from New England to Florida and west to the Mississippi basin and Ontario, south-west to Texas; introduced to Britain before 1634, probably from Virginia. This species has no value in British gardens. It has many times been raised from seed at Kew, and the young plants grow freely for a time, but owing to injury by spring frost and the attacks of a parasitic fungus (for which see p. 264) they rarely get beyond 6 ft in height. Early this century a tree at Kew raised from Michigan seed reached a height of 12 ft but became so diseased that it had to be cut down. Since P. occidentalis ranges over many climatically diverse regions, and ascends to 2,500 ft in the Appalachians, it seems to be not beyond the bounds of possibility that there might still be found a form of the western plane capable of growing well in our climate. But even then the attacks of the plane-tree disease Gnomonia veneta, to which this species is very susceptible, would probably make it worthless. Even in the United States it has been supplanted as an ornamental by the oriental and London planes. But before the disease reached this country, probably early in the 19th century, the American plane may have fared rather better than now. At any rate, there is a specimen in the British Museum of the true P. occidentalis taken from a tree growing at Kew in 1781; and in Bishop Goodenough’s Herbarium there is a specimen bearing a mature fruit-ball which almost certainly came from a tree at Kew around that time.
During the 19th century P. occidentalis seems to have become rare in Europe, but some of the trees from the early introductions continued to exist, e.g., in France at Angers and near Montpelier. It also remained in commerce, but often under such incorrect names as “P. macrophylla” and “P. hispanica”. At the present time (1974) there is a promising young tree at Kew raised in 1969 from seeds received from the National Arboretum, Washington, US A. At Borde Hill in Sussex a shrubby specimen has existed in a damp, shady place for about sixty years.
Although the true species has always been rare in this country, its name was once generally used in gardens for P. acerifolia. The first to question the correctness of this identification was the nurseryman Thomas Rivers, who expressed his doubts both to Loudon and Professor Lindley at some time during the 1830s, but apparently neither agreed with him. However, Rivers was vindicated in 1856, when Sir William Hooker, the Director of Kew, wrote to The Gardeners’ Chronicle remarking that a tree in the collection planted as P. occidentalis was not the true species (the tree in question is almost certainly the fine specimen of London plane growing at the end of the Rhododendron Dell). After Hooker’s intervention, and the correspondence that followed, it came to be accepted among the better informed that the plane so common in the parks and squares of London was not P. occidentalis, and discussion shifted to the problem of its identity and origin. But most nurserymen and a surprising number of botanists continued to confuse the two until well into this century.
var. glabrata (Fern.) Sarg. P. glabrata Fern.; P. lindeniana sens. S. Wats., not Mart. & Gal.; P. racemosa sens. Hemsl., not Nutt.; P. densicoma Dode, in part, teste Sarg. – Leaves mostly truncate to shallowly cordate at the base, more deeply lobed than in the typical state, with acute or rounded sinuses, the lobes slenderly acuminate, more or less entire except for small secondary lobes at the base of the blade and sometimes on the central lobe (but the leaves on strong shoots more numerously toothed). Fruit-balls and achenes as in typical P. occidentalis.
Native of N. Mexico (Coahuila, Nuevo Leon, and San Luis Potosi), extending into the USA, where it is common in W. Texas but occurs occasionally farther north and east. It was described from an herbarium specimen originally identified as P. lindeniana, a Mexican species with a more southern distribution. The epithet glabrata refers to the fact that the undersides of the leaves become nearly glabrous, whereas in P. lindeniana they are permanently hairy. Sargent retained the epithet when placing P. glabrata under P. occidentalis, though there does not seem to be any marked difference in leaf-indumentum between the variety and the typical state, unless it be that the young leaves in var. glabrata are less woolly.
It is tempting to suppose that the var. glabrata was introduced to Europe from Mexico at an early date, and that some cultivated planes considered by the early botanists to be intermediate between P. occidentalis and P. orientalis were really this variety and not P. acerifolia.