A deciduous tree of the largest size, frequently over 100 ft high, with a smooth, erect trunk, whose bark peels off in flakes, and a huge rounded head of somewhat contorted branches, the terminal parts of which in large trees are pendulous; young shoots and leaves covered at first with a dense, pale brown wool much of which falls away by autumn. The leaves of mature trees are very variable in shape, even on the same individual. The commonest type of leaf is truncate to shallowly cordate at the base, three- or five-lobed, entire except for a few teeth at the base or sparsely toothed throughout, mostly 6 to 7 in. long and 8 to 9 in. wide (measured between the tips of the two lateral lobes), the central lobe broadest at its base, somewhat longer than wide, separated from the lateral lobes by approximately right-angled sinuses (but by a lesser angle in some small, three-lobed leaves); petiole 2 to 3 in. long. Towards the end of the summer leaves are produced which are deeply cordate at the base, strongly toothed (though sometimes almost entire on old trees) mostly five-lobed, sometimes even seven-lobed; the sinuses are deeper than on the lower leaves, and the central lobe is commonly constricted at the base; these leaves are mostly 6 to 71⁄2 in. long, 8 to 10 in. wide, and have a disproportionately short petiole, which is 13⁄4 to 2 in. long (usually shorter than the depth of the basal sinus). On some shoots a peculiar type of leaf is produced which is smaller than in the previous two types and wide for its length, mostly three-lobed, the lateral lobes spreading almost horizontally; the base is cordate, and at its centre is a triangular wedge devoid of tissue on the outside, its margins being formed by the bases of the two lateral ribs; the petiole in this type of leaf is long in proportion to the size of the blade, e.g. 23⁄4 in. long on a leaf 4 in. long. On the leaves of mature trees the two main lateral ribs meet the central rib at the base of the blade, i.e., there is no tissue between the apex of the petiole and the junction of the main ribs. But this is not always the case on the leaves of the lowermost branches, which are sometimes uncharacteristic both in this respect and in having an unusually broad central lobe. There is also evidence that anomalous leaves are produced after a tree has been heavily lopped, and on second growths, made after damage by frost or the plane-tree wilt disease. The fruit-balls are mostly two to four on each peduncle, about 11⁄4 in. wide, bristly at first, becoming smoother during the winter owing to the breaking off of the styles near their point of insertion; achene with hairs on the body as well as at the base, its head conical, glabrous when mature.
Under the name P. acerifolia have been grouped various intermediates between P. orientalis and P. occidentalis, of whose origin nothing is known for certain, and whose taxonomic status is still undecided. Of these, at least in Britain, is the form, possibly a clone, that came in the last century to be known as the ‘London plane’, and was for a long time confused with P. occidentalis. The description given above is of this plane only; other forms of P. acerifolia are discussed below, and for two very distinct planes usually placed under P. acerifolia, see P. ‘Augustine Henry’ and P. ‘Pyramidalis’.
In its fruits, the London plane is nearer to the oriental plane than it is to the western, but the fruit-balls are fewer on each peduncle and are less bristly when mature. The foliage of a single individual of the London plane is so variable that herbarium specimens rarely show its full repertoire, and can be very misleading. For the most part the leaves are not unlike those of P. occidentalis, especially of its var. glabrata, but the sinuses are somewhat deeper and the central lobe is usually longer than wide. The only leaves that indicate any affinity with P. orientalis are those borne at the ends of strong shoots, which often have the rhombic central lobe seen in most forms of the oriental plane, but their deeply cordate base is not a regular feature of that species. The young leaves are not so densely woolly as in P. occidentalis, and in this respect are more like those of P. orientalis.
Most modern authorities accept that P. acerifolia is a hybrid between P. orientalis and P. occidentalis. The belief finds support not only in the botanical characters of the London plane but also in its great vigour – a common feature of first-generation hybrids between related species – and in the variability of its seedlings. But the theory is still unproven, however likely it may be. It could be tested by making an artificial cross between the putative parents, and this has now been carried out. The cross was made in 1968 at the National Arboretum, Washington, USA, by F. S. Santamour, Jr, and the seedlings will throw much-needed light on this problem once they reach maturity (Amer. Hort. Mag., Vol. 49 (197o), PP. 23-5).
Having at first taken the view that the London plane was a seedling variant of P. orientalis that became fixed by cultivation, Dr Henry later came to accept that it was of hybrid origin, and in his paper ‘The History of the London Plane’ he attempted to show that it had originated in the Botanic Garden at Oxford around 1670.This paper, written in collaboration with Margaret Flood, was published in 1919 in Proceedings of the Royal Irish Academy, Vol. 35 (B), pp. 9-28, and its main conclusions are summarised in Gard. Chron., Vol. 66 (1919), p. 47. The Oxford tree, catalogued by the younger Bobart as Platanus inter orientalem et occidentalem media, is represented by two herbarium specimens dating from the latter part of the 17th century, which Henry identified with the London plane. One of the weaknesses of his argument is the absence of any proof that the tree originated at Oxford. If P. acerifolia is a hybrid between the oriental and western planes it is likely that the cross occurred – very probably more than once – somewhere in southern Europe, and that the Oxford tree, or the seed from which it was raised, came from a botanic garden in that region. But it should be remarked that, judging from one of the two herbarium specimens cited by Henry, it is questionable whether the Oxford tree was P. acerifolia and not some form of P. occidentalis.
Despite the mists that veil the early history of P. acerifolia, it must have been in cultivation in Britain by the middle of the 18th century, since the largest of the existing trees can hardly be less than 200 years old. Being both hardy and vigorous, and easily increased by cuttings, it usurped the place of P. occidentalis and, to a large extent, that of P. orientalis also. With the coming of the industrial revolution and the growth of cities another virtue of P. acerifolia became manifest. It ‘thrives better in and about London than any other park tree; consequently, it has been planted extensively there during the present century, and has succeeded so well that it has become known as the London Plane. In the numerous London squares and gardens it is certainly surprising to see how healthy, clean and fresh looking this Plane appears, particularly in Berkeley, Bedford and Mecklenburg Squares. Although surrounded by myriads of chimneys, its leaves for size and freshness can vie almost with the foliage in the country far removed from smoke and town atmosphere’ (G. Berry, The Garden, Vol: 20 (1881), p. 372). Like so many of his contemporaries, Berry believed that the London plane was P. occidentalis, and referred to it as the “western” plane. There seems to be little doubt that this false western plane, or London plane, is a clone, or a group of very similar clones, distinguished not by any single leaf picked at random, but by a set of leaves, comprising many different shapes but constant from tree to tree. The London plane also has a characteristic crown: the branches are somewhat tortuous, and the perimeter is intricately branched, giving a winter silhouette which is surprisingly delicate for such a robust tree, and very different from that of the coarser and inferior ‘Pyramidalis’, with which the true London plane has been so lamentably confused.
Most of the older trees of P. acerifolia are probably of the London form, and similar planes are cultivated on the continent. For example, F. Jaennicke, in his admirable study of the planes (1892-7), illustrates his account of P. acerifolia with more than sixty drawings of leaves and leaf-sprays from German trees, mostly from old trees in the Stadtpark at Mainz planted early in th ecentury (Abh. Leop.-Carol. Akad. Naturf, Vol. 77 (1901), plates VIII and IX). A match for every one of these leaves could be picked up in St James’s Park or Green Park in late autumn. The Toulouse tree mentioned below is also very similar to the London plane, but it is likely that most trees of P. acerifolia growing in southern Europe differ in one way or another from the London form.
Among the old trees, one that appears to be distinct from the common London; plane is the tree at the north end of the Rhododendron Dell, which, as mentioned in the footnote below, was probably planted in the 1770s. It bears an unusually high proportion of leaves in which the blade is deeply divided into entire lobes and deeply indented at the base; the central lobe is often inordinately long, and its base may reach to within 1 in. or less of the apex of the petiole. Up to six fruit-balls have been found on one peduncle in this plane, and the styles appear to be unusually long. The fruiting specimen depicted in Dr Henry’s paper on the London plane appears to have been taken from this tree (op. cit., plate VI, fig. 3). Of the other specimens listed below, the tree at Witley Rectory is of the same character. See also P. acerifolia ‘Palmata’. Such trees could represent different forms of the first-generation cross (assuming, of course, that P. acerifolia is a hybrid, which is not so far proven).
Especially in the streets of London, planes can be seen which are clearly not the true London plane and are yet quite different from ‘Pyramidalis’, the common street-plane. These nondescripts are younger than the planes of the parks and older squares of central London, and of no obvious merit. Considering that the true London plane and ‘Pyramidalis’ are so easily propagated by cuttings or layers the existence of these oddments is puzzling. The probable explanation is provided by Thomas Rivers, who remarked that British nurserymen, finding P. orientalis hard to propagate, imported seed from France which was in fact P. acerifolia – often grown on the continent as P. orientalis. According to him, the seedlings from these importations resembled the London plane but had more deeply cut leaves (Gard. Chron. (1866), p. 316). It is possible that the use of prunings as propagating material may have resulted in some of these inferior forms being perpetuated. Nondescript planes are to be found in the streets near Kew Gardens and specimens from some of them are preserved in the herbarium. The planes on the Thames Embankment, planted after the foreshore was built up in the late 1860s and early 1870s, seem to be a varied lot and different from the London plane. According to Berry they came from France, which, if true, would bear out Rivers’s statement.
The following are some of the largest specimens of P. acerifolia measured in recent years: Kew, in Rhododendron Dell, 98 × 171⁄4 ft, bole 30 ft (1965); Osterley Park, Hounslow, London, 98 × 171⁄4 ft, bole 30 ft (1965); Barn Elms, London (grounds of the former Ranelagh Club), 103 × 2o1⁄4 ft (1903), 110 × 25 ft (1971); Riverside Gardens, Richmond, London, 123 × 17 ft and 99 × 181⁄2 ft (1952); Montpelier Row, Twickenham, London, 120 × 181⁄2 ft, bole 40 ft (1968); Ravensbury Park, Morden, London, 110 × 191⁄2 ft and 96 × 2o1⁄4 ft (1968); Carshalton, Surrey, in Festival Walk, 123 × 21 ft (1967); Witley Rectory, Surrey, 115 × 20 ft (1965); Albury Park, Surrey, 110 × 151⁄2 ft (1968); Woodcote House, Dorking, Surrey, 90 × 201⁄2 ft (1956); Kelsey Park, Beckenham, Kent, 96 × 21 ft (1957); Woolbeding Rectory, Sussex, 102 × 161⁄2 ft (1957); Blenheim Palace, Oxon, by the Cascades, 120 × 181⁄4 ft (1965); Pusey House, Oxon, 85 × 24 ft, bole 12 ft (1968); Mottisfont Abbey, Hants, 105 × 211⁄4 ft and a double tree 115 × 36 ft (1968); Cirencester Abbey, Glos., 108 × 183⁄4 ft (1972); Woolverstone Hall, Suffolk, 70 × 21 ft (1968); Kings College Meadow, Cambridge, 100 × 181⁄2 ft (1969); Ely Cathedral, Cambs., 104 × 2o1⁄2 ft (1903), 115 × 273⁄4 ft (1969).
var. hispanica (Muenchh.) Bean – See P. hispanica below, and P. ‘Augustine Henry’.
var. minor Ten. P. hispanica Graeffer ex Ten.; P. acerifolia var. hispanica Ten. – The name P. acerifolia var. minor was given by the Italian botanist Tenore to a plane cultivated in the gardens of the royal palace at Caserta near Naples under the name P. hispanica. It had very small leaves, cordate at the base, with triangular, almost entire lobes. Similar forms of independent origin have occurred elsewhere, and may be seedlings of the London plane or similar forms. Here may be mentioned a curious tree at Kew in Syon Vista that came from Van Houtte’s nursery in the 1870s, but under what name is not certain. The leaves are mostly 4 in. or less long, ovate in general outline, broadly cuneate at the base, scarcely lobed, or with a pair of short lateral lobes; leaves at the ends of the shoots are more like those of the London plane, but much smaller.
cv. ‘Palmata’. – According to Thomas Rivers, who imported it from France, this plane makes a vigorous, erect tree; the leaves are more deeply lobed than in the London plane, and persist longer on the tree in the autumn; the bark flakes less (Gard. Chron. (1860), p. 47 and (1866), p. 316). A plane under the same name was sold by Barron’s nursery, Elvaston, near Derby, in the last century. Rivers also mentions ‘Palmata Superba’, which may be the same as the plane sold by Späth’s nursery, Berlin, as “P. superba”. Young plants under both names were growing at Kew in the 1830s, but it is uncertain whether either still exists. There are, however, two fine trees in the collection which may well have come under distinguishing names, since both are very distinct from the ordinary London plane and are certainly worthy of distinction. One grows by the south-east corner of the Herbarium; the other stands north of the planting around King William’s Temple, behind the collection of Japanese cherries.
cv. ‘Pyramidalis’. – See P. ‘Pyramidalis’.
cv. ‘Suttneri’ . – A handsome variegated tree, its leaves being conspicuously blotched, spotted, or patched with creamy white, and sometimes almost wholly of that colour. It was introduced shortly after the middle of the last century, and almost certainly originated as a seedling. It is weaker-growing than the London plane, and rather susceptible to plane-tree wilt. Examples are: Holland Park, London, 54 × 41⁄2 ft (1964); Heath Cottage, Puttenham, Surrey, 73 × 7 ft (1963); National Botanic Garden, Dublin, 60 × 31⁄2 ft (1966). ‘Argentea Variegata’, raised by Messrs Russell, then of Richmond, is similar to ‘Suttneri’, and the two may have become confused; it received an Award of Merit in 1897. In ‘Kelseyana’ (‘Aureo-variegata’), raised in the USA, the leaves are variegated with yellow. This clone (and ‘Suttneri’) were both wrongly placed under P. occidentalis by Jaennicke.
P. hispanica Muenchh. Spanish Plane (of Miller). – In 1770, Muenchhausen gave the name P. hispanica to the plane that Miller had first described in the 1759 edition of his Dictionary. Miller’s description is as follows: “The Spanish Plane-tree has larger leaves than either of the other sorts, which are more divided than those of the Occidental plane-tree, but not so much as those of the Eastern. Some of the leaves are cut into five and others but three lobes; these are sharply indented on the edges, and are of a light green; the foot-stalks are short, and covered with a short down. This is by some called the middle Plane-tree, from its leaves being shaped between those of the two other sorts. It grows rather faster than either of the other sorts, but I have not seen any very large trees of this kind.’
Muenchhausen added nothing of significance to Miller’s description, but made the suggestion that P. hispanica might be a hybrid (Vermischung) between the oriental and western planes.
Unfortunately no specimen of Miller’s Spanish plane can be traced, and its identity is uncertain. It is very probable – but perhaps unprovable – that it was the London plane or at least some very similar form. Miller’s description agrees quite well with the London plane, and it is surely significant that Aiton gave ‘Spanish plane-tree’ as the vernacular name for P. orientalis var. acerifolia Ait., which is usually supposed to be the London plane. But Miller himself considered the maple-leaved plane (acerifolia) to be distinct from the Spanish plane, and there is some evidence that the London plane was grown by Miller at Chelsea under the name P. occidentalis. Since the evidence is so contradictory, the name P. hispanica Muenchh. must be regarded as of uncertain application. For the plane that Henry considered to be Miller’s Spanish plane, see P. ‘Augustine Henry’.
Later uses of the name P. hispanica should be mentioned, though they do not necessarily have any bearing on the typification of Miller’s Spanish plane. The identity of the plane distributed by Loddiges’ nursery under the name P. hispanica is uncertain; according to Loudon it resembled P. orientalis but had ‘longer’ leaves. P. hispanica Hort. ex Gord. (Garden, Vol. 1 (1872), p. 588) is a form of P. occidentalis and is probably the plane distributed commercially as P. hispanica integrifolia or P. integrifolia, which was placed under P. occidentalis by Wesmael as var. hispanca. The leaves of this plane, which are matched by those of some wild trees, are very shallowly lobed and some are almost circular in outline, but with a deeply cordate base. Finally, a tree cultivated as P. hispanica at Caserta was referred by Tenore to P. acerifolia as var. minor (q.v.).
P. hybrida Brot. – The name P. hybridus [sic] was given by the Portuguese botanist Brotero in 1804 to a plane described by him as fast-growing, with subpalmate, five-lobed leaves, the lobes acute and dentate. He suggested it might be a hybrid between P. occidentalis and P. orientalis, or a variety of the latter. The name P. hybrida has priority over P. acerifolia Willd., and is used by some authorities. But the identity of Brotero’s plane is uncertain, and it therefore seems preferable to retain the more familiar and better established name P. acerifolia for this group. In the Prodromus Alphonse de Candolle gives P. hybrida Brot. as a synonym of P. occidentalis.
The specimens of P. acerifolia in Willdenow’s herbarium have not been seen. But the French authority Dr P. Rivals, who examined them, has presented to Kew a set of specimens taken from a single tree of P. acerifolia growing at Toulouse and has annotated two of these as matching the specimens of P. acerifolia in Willdenow’s herbarium. The Toulouse tree is evidently very similar to our London plane.