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The genus Platanus is a small genus of six species of trees native to the Northern Hemisphere. They are the sole members of the family Platanaceae. They are all large trees to 30-40 m tall, deciduous (except for P. kerrii), and are mostly found in riparian or other wetland habitats in the wild, though proving drought tolerant in cultivation away from streams.

They are known as planes in the Old World, and as sycamores in North America. Elsewhere, the name "sycamore" refers to either the fig Ficus sycomorus (the species originally so named), or the Sycamore Maple, Acer pseudoplatanus.

The reduced flowers, borne in balls (globose head), 3 to 7 hairy sepals (may be fused at base), and 3 to 7 (or no) spathulate petals. The male and female flowers are separate, but 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 with 3-8 stamens; the female has superior ovary with 3 to 7 carpels. Plane trees are wind-pollinated. Male balls fall off branch after shedding their pollen. The female flowers, on the other hand, remain attached to the branch firmly.

After they withered, the female flowers become achenes that aggregate on the 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 3 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 the wind dispersion of the fruits like dandelion.

The mature bark peels (exfoliate) off easily in irregularly shaped patches, proucing a mottled, scaly appearance. Very old barks may not flake off, but would crack instead. The base of leaf stalk (petiole) is enlarged and completely wraps around the young stem bud in its axil. The bud will be exposed only after the leaf falls off.

The following are recognized species of plane trees:

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.

There are fossil records of plane trees as early as 115 million years (the Lower Cretaceous). Despite the geographic separation between North America and Europe, species from these continent remain interfertile, resulting in hybrids such as London Plane.

Under the Cronquist system, Platanus was placed in the order Hamamelidales. Newer systems place it in the order Proteales.

External links

• Great Americans: The Sycamores from The Monday Garden
• Botany of Plane trees
• Plane trees
• Photos with descriptions