Flowers of a form of Platanus orientalis;
showing the prominent female flowers, and also
the less showy male flowers to the left.
The genus Platanus is the only one in the dicotyledon family Platanaceae. It arose early in the evolution of flowering plants, and fossil specimens are known from the earlier Cretaceous period, over 100 million years ago.
There are about 6-10 species of plane tree, depending on botanic authority. New species have been described recently for North America. All plane trees are from the northern hemisphere, mostly in temperate regions. Two species are from the Old World; Platanus kerrii is the only tropical species, found in Indochina, and it is sometimes placed in a separate subgenus. Platanus orientalis is found from West (and perhaps South) Asia and South Europe. Several others, including Platanus occidentalis, Platanus racemosa, Platanus wrightii, Platanus lindeniana and perhaps others are from North America. Platanus kerrii is evergreen, and the others are deciduous.
Flowers of a form of Platanus orientalis;
showing the prominent female flowers, and also
the less showy male flowers to the left.
Their preferred natural habitat is river valleys and wetlands in warmer temperate regions, but they can tolerate dry conditions after establishment. All are large trees, generally 20-50m high. A common characteristic is flaking bark that peels away in sections or sheets, leaving a dappled trunk.
Leaves are borne alternately on the stem. They are always simple (not split into leaflets). In most species they are palmately lobed and veined, (in Platanus kerrii leaves are unlobed, pinnately serrate and pinnately veined). Juvenile leaves are distinct from adult leaves, being more deeply and narrowly lobed in most species. The axillary bud on the shoot is covered completely during the growing season by the base of the petiole, which may be swollen to accommodate it. The shoots and young leaves are covered by hairs or a fine down when young, this is probably to protect the young tissue from sunlight and water loss. The hairs are usually shed as the leaves mature, but sometimes they are partially retained on the underside of the leaves. Stipules are usually present, part of each stipule forming a tube around the shoot, the rest of it forming a leaf-like extension.
London plane fruit
Plants are bisexual - both sexes borne on the same tree. Male and female flowers are borne on separate spherical inflorescences, which hang on fibrous stalks. They are wind pollinated. The female flower-heads are more showy, generally greenish flushed red or purple, colour varying with the clone, sometimes entirely green or a bright sea-green. The flowers form dense spherical heads, sometimes separately stalked, 1 to 12 on a stem. Of the forms seen in Britain, the oriental plane has the greatest number of female flower heads per stem, up to 6. There may be between 3 and 8 each of petals and sepals. There are between 3 and 4 anthers on the male flowers and between 6 and 9 pistils on the female flowers. The flowers may be covered by hairs as in the leafy shoot. Each female flower becomes an achene, united with the others on the flower-head to form the spherical fruit. Often the styles persist to form bristles or prickles on the seed, and they aid dispersion of the seed. The fruits persist through the winter on the temperate species. They then distintegrate in early spring, generally while still on the tree, releasing the achenes.
The generic name Platanus was published by Linnaeus. The oriental and occidental planes were known to him and named by him.
The common name for the genus is 'plane' in British English, 'sycamore' or 'planetree' in US English. Variations of 'platane', 'platano' are used in much of Europe, names derived from the Greek 'platanos' or 'platus', meaning broad, and referring to the leaves. 'Chenar' or variations of it are used in the region from Turkey to Kashmir. In Kashmir itself, the name 'bouin' (derived from the goddess Bhavani) was originally used. In Arabic, the name 'dulb' is used.
There is some disagreement about the correct specific name for the London plane. The principal contenders are;
Platanus x hispanica Muenchhausen. This name was published in 1770, based on a description by Miller from a now untraceable source. (Augustine Henry believed that Miller was describing the clone now named after him, P. 'Augustine Henry'.)
Platanus x hybrida Brotero (1804). This was based on a tree which Brotero suggested might be a hybrid, but which Bean feels cannot be reliably identified.
Platanus x acerifolia Willdenow, based on a descripton by Aiton. This name was published in 1805, and hence both other names above have priority. However, this name is in widespread use now, much more so than its closest contender, P. x hispanica. Bean makes a case for it to continue to be used on the basis that the specimens described for the other two names cannot be reliably identified. Santamour and McArdle describe his arguments as 'not entirely convincing', but agree that this name should continue to be used. It is used on this website.
Naming according to some standard works and institutions;
The hybrid plane trees that are grown in London are normally described as belonging to a single species, Platanus x acerifolia. It is clear on close inspection that individual trees vary, though the variation can easily fit into one species. Some of the distinct observed forms are described on this website, together with a summary of the information in the literature.
Commonly, all forms of the hybrid plane are called the London plane in English, both in Britain, and commonly in other countries. However, W. J. Bean, in Bean's Manual, uses the term 'London Plane' refers to a single distinctive clone or group of similar trees, which is often found in Central and Inner London. He also used the name 'London Form' at least once to refer to this distinctive clone. Because of the possible confusion, in the rest of this web site I use the term Platanus 'London form' or Platanus x acerifolia 'London Form' to describe this particular clone. It constitutes a minority of the trees in the city, especially among the younger plantings in suburban London.
The wider terms Platanus x acerifolia and 'London plane' are used in this website to describe all the hybrid forms collectively, in accordance with common usage.
Santamour and McArdle call this same clone 'London', again after Bean. They (being Americans) also suggest that the term 'London plane' is used in Britain to describe only the above clone - while it is true that Bean used it thus, it is also true that most of the rest of Britain has consistently called all forms of the hybrid plane the London plane.
Bean may have included the trees that I refer to as the 'Westminster Form' together with the 'London Form', since the trees are very alike in many characteristics.
Comparison table for some characteristics of the three most commonly seen plane species.
| Number of distinct leaf lobes | Ratio, width of main lobe to length of lobe. | Number of fruits per stem | |
| Platanus occidentalis | 3-5 | lobe is usually wider than long | 1-2 |
| Platanus x acerifolia | 5, rarely 3 or 7. | lobe is usually about as wide as long | 2-4 |
| Platanus orientalis | 5-7 | lobe always longer than wide | 2-6 |
Pictures below (not to same scale) shows some variations in leaf shape
There is considerable variation within Platanus orientalis. This can be noted in the different leaf shapes, branching patterns, and bark formation of the trees found in London.
The different clones of Platanus x acerifolia can vary in most of the visible characteristics. These include the leaf shape and colour, glossiness, colour and density of the hairs covering expanding leaves, bud shape and colour, stipules and their persistence, shoots, fruit size, bark colour, persistence of bark, branching habit, and the straightness of branches. In addition some of these characteristics can vary with the age and vigour of a tree, the season, and according to what part of the tree is being considered. One usually has to look at a combination of these factors to be have any idea which clone a tree belongs to.
The National Trust holds an NCCPG National Collection, of seven forms of Platanus, at Mottisfont Abbey in Hampshire. Other significant British collections are held at principal botanic gardens, including particularly Kew Gardens and The Hillier Arboretum, Hampshire.
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27-Apr-2007