Secret life of knobs and pillys

Philip Hoare does a little muck-raking on our plant life; Flora Britannica by Richard Mabey, Sinclair Stevenson, pounds 3

Take a suburban train out of any city or town, put down your paper and pay some attention to that green stuff at the side of the tracks. Britain's history in plants is passing you by, a bio-diverse record of human habitation: the ubiquitous vivid purple of rosebay willow herb, named fireweed because it was thrown up by the great 19th century rail network; the equally common buddleia, the butterfly bush, its tenacity in seemingly soil-less vertical cracks a reminder of its origins in the mountains of China; the sudden burst of scarlet poppies germinated from newly-disinterred seed, an echo of Flanders fields where the more deadly machinations of man enabled them to bloom. Wild plants, by definition, are everywhere: only yards from a south London station last week I saw clumps of brown velvet bulrushes as rural as you like, albeit decoratively surrounded by Tennents Super beer cans.

With its "urban commons" and modern folklore, Richard Mabey's book is no update of the Diary of an Edwardian Country Lady. "When wild flowers are dragged willy-nilly into shampoo advertisements and state rituals, maybe it is time to ask whether the particular plants themselves have any meaning left for us, or whether they have become purely notional, registers of a fashionably Green 'life style'." Drawing on his own researches and contributions from the plant-aware public, Mabey's book is a botanical vox pop, a green Mass Observation: from the primeval horsetails, Equisetaceae, briskly updated as "Lego plants" (pull 'em apart and put 'em back together again) to the tragedy of the elms, doomed to regenerate as suckers only for Dutch Elm disease to strike again as they reach maturity, the fungus Ceratocystis ulmi severing their water supply and killing them through thirst.

The cycles of life and death and sex are as dramatic in botany as in the rest of creation and like any potential best seller Flora Britannica has a good smattering of sex. Natural nomenclature is phallicentric enough to rival Mapplethorpe: dog's cock, priest's pilly and cuckoo pint (pint being short for pintle or penis) exhibit a rural preoccupation with matters genital. One informant tells Mabey that the youthful fishermen of the Isle of Man still used, in the 1930s, the milky sap of the sun spurge Euphorbia heliscopia to "get themselves excited" - hence its indelicate local name, "big knobs"; or "Saturday night pepper". Elsewhere we are told that the yellow flowers of the sweet chestnut smell distinctly of semen and that the thick furry grey leaves of the great mullein give rise to its modern appellation, the "Andrex plant". Less intimate cleansing may be had from the common nettle, which gypsies grasp by the stem and pull through work -smeared hands; the effect is also supposed to prevent against arthritis. The Romans used nettles in "therapeutic self-flagellation" to warm up the circulatory system in our chilly climate and in the First World War the Germans wove them into cloth. And here's a useful tip from a Devon boy on how to eat the raw leaves: "The trick is to roll them up in a special way with the tongue, making sure there is plenty of saliva to coat them."

There are elegant essays on significant trees such as yews, hollies, elms and oaks; ancient inhabitants of our land whose heartwood-decayed trunks resemble "a wooden cave system more than a tree." Mabey deftly evokes the atmosphere of plants with a particular taste for the macabre: the Gothic tracery of ivy, the surreal weirdness of the giant hogweed; the sinister, malodorous henbane which supplied Dr Crippen with the means to his poisonous ends. A fig tree grows out of a Watford grave, "originated in a snack taken by the unfortunate occupant." His use of art, literature and allusion is illuminating: Ruskin on the field poppy as "painted glass; it never glows so brightly as when the sun shines through it." But Mabey is eminently able to match such poetry, describing the delicate beauty of the hound's tongue, its flowers a "colour whose tone is more like that of dyed fabric - worn purple velvet, perhaps - than a bloom. The 17th- century herbalist John Pechey described them as 'sordid red'."

Inevitably, folk tales abound in Mabey's account, but with startlingly modern correlations, vividly illustrated by a chap who has a nasty brush with a chain-saw. In an episode straight out of Casualty, the intrepid victim cycles four miles to a comfrey-plenty place, digs up some of the plant root and scrapes it into a thick paste which sets hard and eventually drops off, leaving our hero with a "surprisingly small scar". The intoxicating properties of plants are well covered, but foraging druggies will be disappointed: opium poppies just don't make enough latex in our climate and legally field-grown cannabis hasn't got the THC to get you high. In one anecdote, the book describes a police raid on a secondary school where they confiscated a horse chestnut sapling, confusing its finger-like leaves for those of Cannabis sativa.

If you want to know what Berkshire schoolchildren use for itching powder (crushed plane seeds) or what cured George III's insomnia (hops), the details are all here, exquisitely illustrated and elegantly edited. But the cumulative effect of this body of knowledge is ultimately humbling: less about what use we can put plants to than the intrinsic sanctity of nature itself. In the habitat unfriendly late 20th century, this can no longer be merely a moot point; and those who would seek to plough through the water meadows of Salisbury should be force fed Flora Britannica until they see the evil of their tarmac ways.