Platanus

Standard Cyclopedia of Horticulture

Platanus (its ancient Greek name). Platanaceae. Plane-tree. Buttonwood. Ornamental 'trees with handsome dense foliage, often planted as shade and street trees. Deciduous, with the bark exfoliating in thin plates, but at the base of older trunks the bark is persistent, of darker color and furrowed: stipules conspicuous, usually connate into a tube, with spreading lf.-like margin; petiole with the enlarged base inclosing the axillary bud: lvs. palmately lobed, covered densely with stellate hairs when young: fls. monoecious, in dense globular heads, staminate and pistillate similar, but on separate peduncles; sepals and petals 3-8; staminate with 3-8 stamens, pistillate with 3-8 pistils with elongated styles: fr.-heads consisting of numerous narrowly obconical, 1-seeded nutlets surrounded at the base by long hairs.—Six or 7 species are known in N. Amer., south to Mex. and from S. E. Eu. to India. The planes are handsome trees with large and palmately lobed leaves and small greenish flowers in drooping heads, followed by similar heads of fruits remaining on the branches during the winter. The smooth light-colored often almost creamy white bark of the branches and limbs, usually mottled by darker blotches of the older bark, which peels off in large thin plates, gives the tree a very characteristic appearance in winter, while in summer the plane-tree, with its large head of dense bright green foliage and with its massive trunk is a beautiful and majestic shade tree. The native P. occidentalis is hardy North and P. aceri- folia and P. orientalis hardy as far north as Massachusetts, while the southwestern and Mexican species cannot be cultivated in the North. From time immemorial, the oriental plane, which was well known to the ancient Greek writers, has been famous for the large size it attains—trunks of 30 feet in diameter and more are reported to exist—and has been planted as a shade tree in western Asia and southern Europe, and today it is still one of the favorite street trees throughout the temperate regions of Europe. It has also been recognized in this country as one of the best street trees, even to be preferred to the native plane, which, unfortunately, suffers from the attacks of a fungus, Gloeo- sporium nervisequum, while the oriental is not injured by it. The plane-trees stand pruning—even severe pruning—well. To what extent they are sometimes pruned in European cities without losing their vitality is shown in an interesting illustration in "Forest Leaves," Vol. III, p. 97. They are also easily transplanted even as larger trees. They grow best in a deep and rich moist soil. Propagation is by seeds sown in spring and only slightly covered with soil and kept moist and shaded; also by cuttings of ripened wood and by greenwood cuttings under glass in June taken with a heel, and sometimes by layers. Varieties are also sometimes grafted in spring on seedlings of one of the species. The stellate hairs of the young leaves when detached by the wind, sometimes float in great quantities in the air and are liable to cause irritation and sometimes inflammation of the mucous membranes of the eye, nose, and mouth. But as this is likely to occur only during a very limited period late in spring it can hardly be considered as a serious objection to the use of platanus as a street tree. P. vulgaris, Spach, comprises all species of the genus.—P. Wrightii. Wats. Tree, to 80 ft., often divided into several sts.: lvs. usually cordate or truncate, deeply 3-7-lobed, with lanceolate, acuminate, entire or dentate lobes, tomentose beneath or nearly glabrous at length, 6-8 in. long: fr.-heads racemose, rather smooth, each on a short stalk. New Mex. and Aris. to Calif. S.S. 7:329. The other species, as P. mexicana, Moric., which is sometimes planted as a street tree in Mex., P. Lindeniana, Mart. & Gal., and P. glabrata. Fern., all natives of Mex., are not yet intro. Alfred Rehder. The above text is from the Standard Cyclopedia of Horticulture. It may be out of date, but still contains valuable and interesting information which can be incorporated into the remainder of the article. Click on "Collapse" in the header to hide this text.

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Leaves and fruit of a London Plane
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"Plane tree" redirects here. In mathematics, "plane tree" refers to a tree embedded in the plane.

Platanus is a small genus of trees native to the Northern Hemisphere. They are the sole members of the family Platanaceae.

They are all large trees to 30–50 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 Europe, and as sycamores in North America. (Outside North America, the name "sycamore" refers to either the fig Ficus sycomorus, the plant originally so named, or the Great Maple, Acer pseudoplatanus.)

Natural history

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

Bole of an aged Platanus, in Trsteno, near Dubrovnik, Croatia

After being pollinated, 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 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 like dandelion.

The mature bark peels (exfoliates) off easily in irregularly shaped patches, producing a mottled, scaly appearance. Very old bark may not flake off, but can crack instead. The base of the 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.

Phylogeny

There are two subgenera, subgenus Castaneophyllum containing the anomalous P. kerrii, and subgenus Platanus, with all the others; recent studies in Mexico 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. 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 continents will cross readily resulting in fertile hybrids such as the London Plane.

Species

The following are recognized species of plane trees:

Scientific name	Common name	Distribution	flowerheads	Notes
Platanus chiapensis	Chiapas Plane	southeast Mexico	?	Subgenus Platanus
Platanus gentryi	Gentry's Plane	western Mexico	?	Subgenus Platanus
Platanus × hispanica (P. occidentalis × P. orientalis; syn. P. × acerifolia)	London Plane	Cultivated origin	1-6	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 or Buttonwood	eastern North America	1-2	Subgenus Platanus
Platanus orientalis	Oriental Plane	southeast Europe, southwest Asia	3-6	Subgenus Platanus
Platanus racemosa	California Sycamore	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

Diseases

Avenue of plane trees

Main article: List of sycamore 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. 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.

References

• Feng, Y.; Oh, S.-H., & Manos, P. S. (2005). Phylogeny and Historical Biogeography of the Genus Platanus as Inferred From Nuclear and Chloroplast DNA. Syst. Bot. 30 (4): 786-799 abstract
• Nixon, K. C. & Poole, J. M. (2003). Revision of the Mexican and Guatemalan species of Platanus (Platanaceae). Lundellia 6: 103-137 abstract.

External links

• Botany of Plane trees
• Flora of North America: Platanus
• Photos with descriptions
• A developmental and evolutionary analysis of embryology in Platanus (platanaceae), abasal eudicot, abstract of article by Sandra K. Floyd et al. in American Journal of Botany, 1999;86:1523-1537.