How can you display the Maven dependency tree for the *plugins* in your project?

The output via mvn -X will printout the information indirectly. Currently there is no other option to get the dependencies of a Maven-Plugin.

Update You can use the following command to get a list of plugin dependencies (resolve-plugin goal from dependencies plugin):

mvn org.apache.maven.plugins:maven-dependency-plugin:2.10:resolve-plugins

The shorter version is (and it is a bad habit to specify plugin versions)

mvn dependency:resolve-plugins