| Platanus | |
|---|---|
| Leaves and fruit of a London Plane | |
| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Eudicots |
| Order: | Proteales |
| Family: | Platanaceae |
| Genus: | Platanus |
| Species | |
|
See text |
|
Platanus ( /ˈplætənəs/)[1] is a small genus of trees native to the Northern Hemisphere. They are the sole living members of the family Platanaceae.
They are all large trees to 30–50 m tall. All are deciduous, except for P. kerrii, and are mostly found in riparian or other wetland habitats in the wild, though proving drought-tolerant in cultivation. The hybrid London Plane has proved particularly tolerant of urban conditions.
They are often known in English as planes or plane trees. Some North American species are called sycamores (especially Platanus occidentalis[2]), although that term also refers to either the fig Ficus sycomorus, the plant originally so named, or the Great, or Sycamore Maple, Acer pseudoplatanus.[2]
Contents |
The flowers are reduced and are borne in balls (globose heads); 3–7 hairy sepals may be fused at the base, and the petals are 3–7 and are spatulate. Male and female flowers are separate, but borne on the same plant (monoecious). The number of heads in one cluster (inflorescence) is indicative of the species (see table below). The male flower has 3–8 stamens; the female has a superior ovary with 3–7 carpels. Plane trees are wind-pollinated. Male flower-heads fall off after shedding their pollen.
After being pollinated, the female flowers become achenes that form an aggregate ball. Typically, the core of the ball is 1 cm in diameter and is covered with a net of mesh 1 mm, which can be peeled off. The ball is 2.5–4 cm in diameter and contains several hundred achenes, each of which has a single seed and is conical, with the point attached downward to the net at the surface of the ball. There is also a tuft of many thin stiff yellow-green bristle fibers attached to the base of each achene. These bristles help in wind dispersion of the fruits as in the dandelion.
The leaves are simple. In the subgenus Platanus they have a palmate outline. The base of the leaf stalk (petiole) is enlarged and completely wraps around the young stem bud in its axil. The axillary bud is exposed only after the leaf falls off.
The mature bark peels off or exfoliates easily in irregularly shaped patches, producing a mottled, scaly appearance. On old trunks, bark may not flake off, but thickens and cracks instead.
There are two subgenera, subgenus Castaneophyllum containing the anomalous P. kerrii, and subgenus Platanus, with all the others; recent studies in Mexico[3] have increased the number of accepted species in this subgenus. Within subgenus Platanus, genetic evidence suggests that P. racemosa is more closely related to P. orientalis than it is to the other North American species.[4] There are fossil records of plane trees as early as 115 million years (the Lower Cretaceous). Despite the geographic separation between North America and Old World, species from these continents will cross readily resulting in fertile hybrids such as the London Plane.
The following are recognized species of plane trees:
| Scientific name | Common name | Distribution | flowerheads | Notes |
|---|---|---|---|---|
| Platanus × acerifolia (P. occidentalis × P. orientalis; syn. P. × hispanica, P. × hybrida) |
London Plane, Hybrid Plane | Cultivated origin | 1–6 | Subgenus Platanus |
| Platanus chiapensis | Chiapas Plane | southeast Mexico | ? | Subgenus Platanus |
| Platanus gentryi | Gentry's Plane | western Mexico | ? | Subgenus Platanus |
| Platanus kerrii | Kerr's Plane | Laos, Vietnam | 10–12 | Subgenus Castaneophyllum |
| Platanus mexicana | Mexican Plane | northeast and central Mexico | 2–4 | Subgenus Platanus |
| Platanus oaxacana | Oaxaca Plane | southern Mexico | ? | Subgenus Platanus |
| Platanus occidentalis | American Sycamore, American Plane, Buttonwood, Occidental Plane | eastern North America | 1–2 | Subgenus Platanus |
| Platanus orientalis | Oriental Plane | southeast Europe, southwest Asia | 3–6 | Subgenus Platanus |
| Platanus racemosa | California Sycamore, Western Sycamore, Aliso | California | 3–7 | Subgenus Platanus |
| Platanus rzedowskii | Rzedowski's Plane | eastern Mexico | ? | Subgenus Platanus |
| Platanus wrightii | Arizona Sycamore | Arizona, New Mexico, northwest Mexico | 2–4 | Subgenus Platanus |
Planes are susceptible to Plane Anthracnose (Apiognomonia veneta), a fungal disease that can defoliate the trees in some years. The worst infections are associated with cold, wet spring weather. P. occidentalis and the other American species are the most susceptible, with P. orientalis the most resistant. The hybrid London Plane is intermediate in resistance.
Ceratocystis fimbriata f. platani, a wilt disease, has become a significant problem in recent years in much of Europe.[5]
Other diseases such as powdery mildew occur frequently, but are of lesser importance.
Platanus species are used as food plants by the larvae of some Lepidoptera species including Phyllonorycter platani and Setaceous Hebrew Character.
The principal use of these trees is as ornamental trees, especially in urban areas and by roadsides. The London plane is particularly popular for this purpose. The American plane is cultivated sometimes for timber and investigations have been made into its use as a biomass crop. The oriental plane has a number of minor medicinal uses.
Most significant aspects of cultural history apply to Platanus orientalis in the Old World.