The other day I visited a psychic medium in Croydon, south-east London. Mavis Grimstick (not quite her real name) boasted an ability to hear the dead — ‘clairaudience’. Her front room, hung with plastic foliate Green Man gargoyle motifs and photographs of Stonehenge, was grimly inimical to mediumship and made me want to make a joke about striking a happy medium. ‘Have you been meditating of late? No? ’Cos I’m getting a gorgeous greenish light off of you, and it’s making me feel ever so sunshiny.’ She fluttered her hands. ‘Yes, I like the psychic aura that you have, but why do I see Stonehenge?’ (The roar of an airplane coming in to land over Gatwick muted my reply.) ‘Are you the sort that reaches out for the ancient understanding?’

The medium might have hailed from the pages of Uprooted, Nina Lyon’s gloriously eccentric study of Green Man mythology from medieval times to the present. The Green Man, a pagan forest-god archetype, is commonly found in northern Europe on pub signs, tinned vegetable labels (Green Giant sweetcorn) and Romanesque church ceiling bosses. In the ancient Welsh kingdom of Archenfield and other noted pockets of the paranormal, Green Manifestos (‘Connect with your Shamanic Inner-Self’) circulate among people who converse with trees and eat pharmaceutically active field mushrooms. Prince Charles is no longer such a laughing stock, perhaps, if we happily embrace the eco-morality enshrined at Stonehenge and other solstice sites. Still, we must live in disenchanted times if ravers, spiritualist mediums, hedge-funders and ‘cagoule people’ of every stripe increasingly turn to the Green Man as a sex-magick master of misrule and ozone-friendly woodland sprite.

There is something dark and morose about this chap. Rarely is the Green Man represented as smiling or benevolent. Hitler’s chief race ideologist, the Tallinn-bon Alfred Rosenberg, could almost have co-opted the Green Man’s life-force into his Aryan race-soul paganism. ‘The Nazis were the first European Green Party’, argues Lyon. Nazis lived in a world of Teutonic pagan myths, where symbols appropriated from the Wotan and Beowulf legends (shields, swords, lances) served to establish a sturdy Hitlerite bond of brotherhood and soil; Jews had no place in this dark, poisonous green Fatherland.

Green Man symbolism abounds in the forests of south-west Germany. Beardy, leaf-sprouting heads glower from the cloister roof of Trier cathedral in the Rhineland, while in the Harz mountains a vegetation spirit known as the Brocken Specter leaves a trail of lichen as he clomps about the crags by night. According to Lyon, the term ‘Green Man’ was coined by Julia Hamilton, Lady Raglan, in her 1939 Folklore Journal article on pagan church symbolism. No simple stock image of the Green Man exists; subsets of the Green Men elide in the folk memory with the ritual May Day figure of Jack-in-the-Green (first recorded in England in the 16th century), the medieval Green Knight and the horned Roman forest-god Sylvanus. Visually, what these Bacchic offshoots have in common are extruded leaves, rude poking tongues and other fertility cult atavisms.

In a spirit of subversion, Lyon decides to start her own neo-pagan swingers’ club near her home in (where else?) Hay-on-Wye. The locals refuse to give her the green light. For all their talk of getting laid on ley-lines, the inhabitants of Brecknockshire appear to be a prudish lot; they shun Wicker Man-style exhortations to forest sprites and midsummer sex fests. Lyon considers Green Man sandstone carvings in Herefordshire, stained-glass windows in Snowdonia, and leaf-disgorging medieval misericords in Ludlow. In their different ways, Green Man figures all served to remind our ancestors of the superior force of nature over human endeavour.

Along the way, Lyon digresses somewhat bizarrely on the Bromley punk-rock scene, ambient techno music and shadowy conventicles such as the Knights Templar and the Hermetic Order of the Golden Dawn. Clearly impatient of extremist New Age flim-flam, she is often a sardonic presence during her ‘hunt’ for Green Man marvels. She recruits a Black Mountain animist to help her ‘connect shamanically with trees’ but, sacrilegiously, she drives an eco-unfriendly SUV. Distinguished by the excellence of its writing and its quirky, hobbyhorsical discursiveness, Uprooted is very much a book for our confusing and ever more confused times.

Meanwhile, the Madame Sosostris of Croydon continued to insist that I was bathed in a verdant light. ‘And you will be bathed in this light until the time you get cured.’ (The consultation was a snip at £150.) The medium was possibly mad as well as, surely, a mountebank. When she accurately divined not only the date of my mother’s birth but her maiden name, however, I was not so sure. I left the medium to her Green Man spook-dabbling; on my way home I was alarmed to find a spinach-coloured vegetation issuing from my nostrils.