Written by Dr. Sarah Dooling
Our cultural appreciation of trees is often tied to distinct physical characteristics of trees. The American Sycamore (Platanus occidentalis) can grow up 175 feet tall and 14 feet wide, sometimes creating a canopy more than 70 feet in diameter! In North America, there are stories of early colonial settlers living in the hollowed out portions of sycamores while they built log cabins (see Donald Peattie, A Natural History of Trees, 1950). Sycamores are also associated with sustaining troops in the American Civil War during prolonged periods. The LaFayette Sycamore in Pennsylvania was used to keep troops warm during the winter encampment of 1777-1778 – which makes this particular tree 275-325 years old!
Sycamores are also known as American planetree, buttonball tree, or buttonwood. The name of the tree comes from the Greek word sukomoras, which is a native Mediterranean fig tree. Botanists speculate that English colonialists named the sycamore tree because its broad leaves reminded them of the English Sycamore tree. Sycamores are also called “ghost trees” because of their brilliant white bark that appears to be shedding. This process of exfoliation is much more visible in sycamores than in other trees. As branches thicken during the summer months of rapid growth, the brittle bark splits apart and flakes off, revealing the speckled inner bark of greens, greys and browns. This is the new wood growing underneath the bark. Unlike other trees, the bark of sycamores is rigid and not able to stretch as the trees grow. Only by exfoiliating its bark, can these trees continue to grow. Some people call this tree Lacewood because of its shedding bark.
The American Sycamore is one of the largest broadleaf tree species in North America. The historic range extends from southern Ontario to Florida, then verges west to Michigan, then down to Nebraska and Texas. Sycamores thrive in moist, rich soils found in floodplains and bottomlands. Some botanists think that exfoliation is an adaptive response to the tree living near water where the soils are saturated with water and oxygen is limited. A thin bark might be better able to absorb oxygen and compensate for the absorption deficiency of the roots.
The alternating leaves can be quite large, measuring 4”-6”, and exhibit short hairs on the stems and veins giving the leaves an overall fuzzy appearance. The leaves turn a pale yellow in fall. Given the large size of this tree, the trunk often splits close to the ground. The branches twist and contort in unusual ways contributing to its whimsical shape. The sycamore fruit is a small ball that ripens in October and breaks up into dozens of tiny seeds with little brown hairs that become wind borne. Trees have both male and female flowers.
Sycamores are fast growing and love direct sun. Saplings can grow 10 feet in a single year under ideal conditions! They also grow well in compacted soils and contaminated environments, which is one reason why sycamores are often used as a street tree in cities. However, American sycamores are vulnerable to anthracnose infections (a fungal disease that appears when the weather is cool and wet; it results in small, irregular yellow or brown spots on the leaves). The fungus causes the leaves to fall off prematurely and can eventually kill trees if not treated. Leaf scorch is a more deadly threat. Leaf scorch is a non-infectious physiological condition caused by trees living in unfavorable environmental conditions, which means that sometimes urban conditions are not well tolerated by sycamores. The leaf margins and tips become brown, and the leaf veins darken, which leads to wilting and abscission (a fancy-pants word meaning natural detatchment of parts from a plant) of the leaf.
Because of these risks, urban arborists tend to plant sycamore hybrids, such as the London planetree or, here in Central Texas, Mexican sycamore (Platanus mexicana), which are more disease resistant. The Mexican sycamore is not vulnerable to these diseases and is well adapted to dry, rocky alkaline soils as well as moist soils. Their inner wood is shiny white, which makes for a stunning tree in the winter. Many landscape architects in Austin and Dallas plant this tree – so when you go to the Home Depot store in the Mueller Development, take a close look at the sycamore trees in the parking lot and decide for yourself which Platanus you’re looking at.
If you are interested in a large shade tree, and have rich, moist soil, then an American sycamore is a fantastic choice. They thrive in large, open areas so be sure to give the tree ample room to grow. To minimize the risk of anthracnose infection, prune the tree regularly and water weekly. Be sure that your planting site has full sun!
Sycamores are some of the oldest trees on the planet! They are gentle, majestic creatures that remind us of the co-evolutionary relationships between people and trees, a relationship that offers protection, shade and a unique aesthetic in a sea of concrete.
Click here to read pt.1 of August’s TOTM.