Platanus

# Overview
Platanus (/pltns/)Template:Sfn is a genus comprising a small number of tree species native to the Northern Hemisphere. They are the sole living members of the family Platanaceae.
All members of Platanus are tall, reaching 30 to 50 meters in height. All except for  P. kerrii are deciduous, and most are 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 occidentalisTemplate:Sfn), although that term also refers to either the fig Ficus sycomorus, the plant originally so named, or the Great, or Sycamore Maple, Acer pseudoplatanus.Template:Sfn

# Botany
The flowers are reduced and are borne in balls (globose heads); 37 hairy sepals may be fused at the base, and the petals are 37 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 38 stamens; the female has a superior ovary with 37 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 2.54 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.

# Phylogeny
There are two subgenera, subgenus Castaneophyllum containing the anomalous P. kerrii, and subgenus Platanus, with all the others; recent studies in MexicoTemplate:Sfn 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.Template:Sfn 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.

# Species
The following are recognized species of plane trees:

# Diseases
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 platani, a wilt disease, has become a significant problem in recent years in much of Europe.Template:Sfn
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.

# Uses
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 is widely used as an ornamental and also has a number of minor medicinal uses.

# Cultural history
Most significant aspects of cultural history apply to Platanus orientalis in the Old World.

# Footnotes