American sycamore

The American sycamore (Platanus occidentalis), also known as American plane, Occidental plane, and Buttonwood, is one of the species of Platanus native to North America. It is usually called Sycamore in North America, a name which can also refer to other types of tree.

Description
Easily recognized by its mottled exfoliating bark. The bark of all trees has to yield to a growing trunk; in the case of the Silver Maple and the Shagbark Hickory the process is not hidden, but the Sycamore shows the fact more openly than any other tree. The bark of the trunk and larger limbs flakes off in great irregular masses leaving the surface mottled, greenish white and gray and brown. Sometimes the smaller limbs look as if whitewashed. The explanation is found in the rigid texture of the bark tissue, which entirely lacks the expansive power common to the bark of other trees, so it is incapable of stretching to accommodate the growth of the wood underneath and the tree sloughs it off.

It forms a massive tree, typically reaching up to 30-40 meters high and 1.5 to 2 meters in diameter when left to grow in deep soils. At its tallest, the species has been measured to 51 meters, and at its largest, it has been measured to nearly 4 meters in diameter. Historical specimens over 5 meters thick have been reported, but verifying the accuracy of these early accounts is seldom possible.

It is often divided near the ground into several secondary trunks, very free from branches. Spreading limbs at the top make an irregular, open head. Roots are fibrous. The trunks of large trees are often hollow.

Another peculiarity is the way the leaves protect the growing buds. Examine a branch of almost any tree in early August and nestled in the axils of the leaves you will find the tiny forming bud which will produce the leaves of the coming year. The sycamore branch apparently has no such buds. Instead there is an enlargement of the petiole which encloses the bud in a tight-fitting case at the base of the petiole.


 * Bark: Dark reddish brown, broken into oblong plate-like scales, higher on the tree smooth and light gray; separates freely into thin plates which peel off and leave the surface pale yellow, or white, or greenish. Branchlets at first pale green, coated with thick pale tomentum, later dark green and smooth, finally become light gray or light reddish brown.
 * Wood: Light brown, tinged with red; heavy, weak, difficult to split. Largely used for furniture and interior finish of houses, butcher's blocks.  Sp. gr., 0.5678; weight of cu. ft., 35.39 lbs.
 * Winter buds: Large, conical, three-scaled, form in summer within the petiole of the full grown leaf. The inner scales enlarge with the growing shoot.  There is no terminal bud.
 * Leaves: Alternate, palmately nerved, broadly-ovate or orbicular, four to nine inches long, truncate or cordate or wedge-shaped at base, decurrent on the petiole. Three to five-lobed by broad shallow sinuses rounded in the bottom; lobes acuminate, toothed, or entire, or undulate.  They come out of the bud plicate, pale green coated with pale tomentum; when full grown are bright yellow green above, paler beneath.  In autumn they turn brown and wither before falling.  Petioles long, abruptly enlarged at base and inclosing the buds.  Stipules with spreading, toothed borders, conspicuous on young shoots, caducous.
 * Flowers: May, with the leaves; monoecious, borne in dense heads. Staminate and pistillate heads on separate peduncles.  Staminate heads dark red, on axillary peduncles; pistillate heads light green tinged with red, on longer terminal peduncles.  Calyx of staminate flowers three to six tiny scale-like sepals, slightly united at the base, half as long as the pointed petals.  Of pistillate flowers three to six, usually four, rounded sepals, much shorter than the acute petals.  Corolla of three to six thin scale-like petals.
 * Stamens: In staminate flowers as many of the divisions of the calyx and opposite to them; filaments short; anthers elongated, two-celled; cells opening by lateral slits; connectives hairy.
 * Pistil: Ovary superior, one-celled, sessile, ovate-oblong, surrounded at base by long, jointed, pale hairs; styles long, incurved, red, stigmatic, ovules one or two.
 * Fruit: Brown heads, solitary or rarely clustered, an inch in diameter, hanging on slender stems three to six inches long; persistent through the winter. These heads are composed of akenes about two-thirds of an inch in length.  October.

Distribution
In its native range, it is often found in riparian and wetland areas. The range extends from Iowa to Ontario and Maine in the north, Nebraska in the west, and south to Texas to Florida. Closely related species (see Platanus) occur in Mexico and the southwestern states of the U.S.A. It is sometimes grown for timber, and has become naturalised in some areas outside its native range. It has grown well in Bismarck, North Dakota, and is sold as far south as Okeechobee. The American Sycamore is also well adapted to life in Australia and is quite widespread across the Australian continent especially in the cooler southern States eg. Victoria and New South Wales.

Cultivation
The sycamore is able to endure a city environment and has been extensively planted as a shade tree. It bears transplanting well and grows rapidly.

Propagation and pests
The American sycamore is a favored food plant of the pest sycamore leaf beetle.

Diseases
American sycamore is susceptible to Plane anthracnose disease (Apiognomonia veneta, syn. Gnomonia platani), an introduced fungus naturally found on the Oriental plane P. orientalis, which has evolved considerable resistance to the disease. Although rarely killed or even seriously harmed, American sycamore is commonly partially defoliated by the disease, rendering it unsightly as a specimen tree.

The disease makes its appearance soon after the leaves have expanded, appearing in the form of small black spots which lie close to the veins. As a result, the half grown leaves turn brown, shrivel, and fall. It is very common in early July to see these trees putting forth their second crop of leaves while the first hang brown, dead, and unsighly on the ends of the branches. This greatly shortens the effective growing season for the plant.

As a result of the fungus' damage, American sycamore is not often planted; the more resistant London plane (P. x hispanica; hybrid P. occidentalis x P. orientalis) being preferred instead.

History
The terms under which the New York Stock Exchange was formed is called the Buttonwood Agreement, because it was signed under a Buttonwood tree.

Sycamore made up a large part of the forests of Greenland and Arctic America during the cretaceous and tertiary periods. It once grew abundantly in central Europe, from where it has now disappeared.