Pointy Galls on Maple Leaves

Question:

 I have noticed multiple, small, vertical "spikes" on many of the leaves of my maple tree in my yard. What is this, and do I need to do anything?

Minnesota Master Gardeners say:

 These abnormal growths are leaf galls. While they may be aesthetically unattractive, they seldom result in harm to the tree so control is not warranted or necessary.

A University of Minnesota fact sheet, Insect and Mite Galls in the Landscape, is available on line at http://www.extension.umn.edu/distribution/horticulture/DG6704.html

The fact sheet discusses how the galls are formed and also contains images of several different types of galls.