One origin of the 'green man' images of the high medieval period is medieval religious folklore. Several 'mystery play' texts, including the Cornish Ordinalia, contain the story of Seth and Adam, which is the first part of the Tale of the Rood. At the conclusion of Seth & Adam, Seth places on his dead father's tongue three seeds taken from the (stolen) fruit from the tree of knowledge of good and evil. Straight away the seeds flourished and Adams face was surrounded by shoots and leaves. With other foliate decotations that image was placed i the roofs of medieval churches and catedrals to remind us that the seed of knowledge of good and evil lie within us all.

This Christian tale, which is not in the Bible, was well known in those days. It has its origins in a pre-Christian Judaic tale that can be found in the Midrash and started in oral tradition.

Sedayne's remarks about Lady Raglan are spot on.

The above is the most credible origi I've come across.

Oll an gwella

Crowdercref