There are a number of trees in my neighborhood which seem to be abnormal. The branches are changing shape, and instead of being round, they have ridges growing lengthwise along them. It makes the branches look misshapen, almost like elongated stars. It looks unnatural, maybe like a disease. I think the trees are maples. Do you know what could be causing this?
There are some trees and shrubs whose branches normally take the form I think you are describing, which is sometimes referred to as winged or alate. I am not aware of maples which do this, so I wonder if perhaps you were seeing sweet gum trees, or Liquidambar styraciflua. According to information from the Mathilda Mathias Botanical Garden in Los Angeles,
“One diagnostic character is the presence of corky wings on young stems. In some cases, wings are due to stimulation of localized phellogens along a stem angle, as in winged euonymus (Euonymus alatus). Wings also occur on young stems of sweet gum (Liquidambar). Longitudinal splitting is the cause of stem wings in certain species of elm (Ulmus.)
Here are more images:
Euonymus alatus
Ulmus alata
Liquidambar styraciflua
According to the book Plant Form: an Illustrated Guide to Flowering Plant Morphology by Adrian Bell (Oxford University Press, 1990), these wings can be part of the way a particular plant grows. The book shows an illustration of metamers (also called phytomers), which are repeated constructional units
(like building blocks) in the plant’s development. From my unscientific perspective, I wondered if the wings might have a leaflike photosynthetic function. I did find an article from the Botanical Gazette from February 1889 (yes, 19th century!) by Emily Gregory which examines this issue. It seems to suggest that the corky wings on the branches may have the function of increasing branch circumference and this may provide the tree with extra protection.
A version of this question and answer appeared in the Spring 2014 issue of the Washington Park Arboretum Bulletin.