One of my favorite authors, Terri Windling (author of The Wood Wife [my long time favorite book of hers] and many other fine books) edited a series of short stories with different aspects of the Green Man several years ago (see: http://www.amazon.com/Green-Man-Anthology-Mythic-Forest/dp/B003F76FMM/ref=sr_1_1?ie=UTF8&qid=1340191170&sr=8-1&keywords=green+man+windling).  She also has an outstanding treatise of art and philosophy on her Endicott Studio site on the Green Man and the Green Woman: http://www.endicott-studio.com/gal/galgreen.html which includes fantastic art by Brian Froud of  Faerie fame.  The image below is copyrighted to Brian Froud and there is a link to his other Green Men on the Endicott Studio site listed above.

With all of his many faces, I have found the Green Man as a guide -- a loving, fatherly type figure.  I suppose this is why/how he is portrayed in the Green Man series to Sylvia.  Years ago, I knew a storyteller from Gambia.  He told me of his cultures views on God and Christ.  He said that God is a laughing God who chuckles over his children and all of their antics on Earth.  I have always enjoyed this positive, warm image of an omnipotent being.  Madeleine L'Engle speaks of "The Laughing Christ" -- a statue that portrays an important piece in her book A House Like a Lotus.  Another portrayal. 

The Muslim faith has Khidr, or the green one.  Al Khidr was a guide to Moses.  Where he sat in the desert, everything turned green.  http://www.spiritandflesh.com/Paganism_Islam_Green_Man_Al_Khidr.htm

More mystery...