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The Monday Garden
Great Americans: The Sycamores

Issue No. 144 - December 26, 2004
by Sue Sweeney

The strange thing about sycamores is that they aren’t very human-friendly, yet we plant a lot of them. The trees get big, fast, and have spreading root systems. The extended roots do make them fairly wind-proof; the trunks won’t fall over on your house. However, the roots clog the sewer and heave the sidewalk, the branches interfere with utility lines, and large limbs drop in ice storms. The early spring flowers can rate a whopping 9 out of 10 on the bad allergens scale. Further, the tiny hairs on the seeds are harmful if inhaled, so, as much as boys love throwing the “itchy balls” at each other; it’s not the best idea – stick with the sweet gum’s “sticky balls”.
picture: planetree, Strawberry Hill Ave Stamford CT early summer 2004; note the maple-like leaves and the zig-zag branching.
Native sycamores aren’t even all that useful to wildlife either. Some of the seeds are eaten by some of the smaller birds (and, of course, squirrels). However, the seeds are usually spread by wind and water, and many other native plants provide much more food and shelter. Even the deer don’t like it much.

I think that we keep sycamores around, despite the draw backs, because they’re interesting, as well as majestic.

For example, did you know that their signature thin, multi-colored bark probably evolved as a functional defense against the host of pests and diseases that attack the buds and leaves? The most famous sycamore leaf disease is a fungus called anthracnose. However, the trees are also subject to powdery mildew, bacterial leaf scorch, ozone damage, and late spring frosts; not to mention the lacebug and a bunch of his friends. Because sycamores can photosynthesize at least 10% of their energy directly through the bark, they are able to overcome early-season defoliation and generate a second set of leaves by early summer. Repeated and severe defoliation can weaken the trees but seldom kills them.

The American sycamore (Platanus occidentalis) (a/k/a buttonwood) is found presiding over floodplains, along wooded streams and in other places in Eastern North America with rich soil with abundant water. The American sycamore’s natural range is said to be Zone 4 to 9 (Maine, south to eastern Mexico, and west to Iowa).

pictures: Sycamores along Morgan Street,and on Morgan Street at the corner of the Hoyt Street Alley, all Stamford CT 2004
The London planetree (Platanus X acerfolia) is a hybrid between the American sycamore and its Asian kin, the oriental planetree (Platanus orientalis). Rumor has it that the tree was not intentionally created, but instead, it was discovered a century or so ago, growing in London where the American and Asian parents had come into proximity. Both the American sycamore and the London planetree are used as street, lawn, and park trees. The London planetree is not on the USA list of invasives, despite its wide use in cultivation.

It’s easy to distinguish the Western native sycamores, the California sycamore (Platanus racemosa) and the Arizona sycamore (Platanus wrightii) from the American. Both of these Western sycamores have star-shaped leaves and very white or near-white inner bark. However, because of the close kinship, it’s difficult to tell the native American sycamore from its half-American progeny, the London planetree.


pictures: young sycamore, Hoyt Street Alley, Stamford CT 2003- 2004
The American sycamore and the London planetree share an unmistakable outline. The fast growing trees get really tall, often towering 90 to 100 feet in the air. The form is a stout and lumpy, but tall and straight-ish trunk with irregular, spreading branches that start low. The twigs zig-zag and this pattern often reflected in the mature branches. The trunk and major branches develop muscular curves that mature into impressive compression bulges like those of a sumo wrestler.
pictures:new sycamore fruit in early summer; last fruit in winter; Hoyt Street and Hoyt Street Alley. 2004
The London planetree resembles its Asian parent in that it often has 2 or 3 seed balls in each cluster; while the American sycamore seed balls come one to a stem. In both cases, the early blooming flowers are followed by tightly packed green seeds that mature to brown, and often persist on the tree over winter. Eventually, the seed ball falls apart, releasing seeds that have tiny parachutes for wind travel but are equally likely to float down the closest stream.
picture 1: planetree leaf starting to show anthracnose damage, Strawberry & Hoyt, 2004
picture 2: leaves of a sycamore sapling along the Mill River at Scalzi Park, summer 2004
The London planetree and the American sycamore have similar raggedy maple-like leaves, 4 to 8” across, with 3 to 5 lobes and irregularly toothed edges. The American sycamore’s leaves are wider than the London planetree’s.

The American sycamore's inner bark is a creamy white; the London planetree's inner bark is usually more yellow.

(Don’t worry if you can’t tell the London planetree and the American sycamore apart, as I’ve overheard professional arborists whispering to each other that they find it nealy impossible at times.)

pictures: checkered bark pattern that forms usually towards the tree base, generally on American sycamores – not plane trees. First picture: planetree,Strawberry Hill Spring 2004; middle and last picture: mature sycamore 3rd Street, 2004
The London planetree is better able to resist the standard sycamore diseases and pests. In addition, it’s cold-hardy to frigid Zone 3, and it doesn’t have the American’s need for abundant water. As such the London planetree is even tougher than its parents, rivaling the pre-historic ginkgo for the title of “World’s Toughest and Most Ubiquitous Street Tree”.

This quote from Floridata.com, a wonderful gardener’s resource, is a good reminder of what these long-suffering street trees have to put up with, while cooling and cleaning our air; shading and decorating our streets and sidewalks; and hosting our squirrels and birds:

“London plane probably is more tolerant of smoke, dust, soot, air pollution, reflected heat, pavement over the roots, wind, heavy pruning, and general abuse than any other tree….”

Sycamores are very long lived, despite being fast growers. Once they reach their full height, they keep getting thicker (like many humans). The American sycamore has been reported to achieve trunk diameters of 10 to 15 feet, and live 500 years. After the first 200 or 300 years, the trunk starts hollow out, probably as way of reducing weight. Interesting tidbit from that collector of arcane forest lore, the USA Forest Service: “generally, sycamore is not dependable for seed after the age of 250 years.”

picture 1: planetree leaf in winter Cummings Park, Stamford CT 2004
picture 2: newly leafed-out planetree Strawberry & Hoyt, 2004
By the way, while some sources suggest that “sycamore” comes from a Native American word, other sources indicate that the word “sycamore” originated in long, long ago in the Mid-East.

Following pictures: planetrees at Stamford CT's Cove Island Jan. 1, 2005


From The Monday Garden. Copyright © by Sue Sweeney. Reproduced with permission. 

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