Six of the 19 endangered plants are now the subject of such schemes, and most of the others are under consideration, as the government would have been able to inform any of the signatories to the treaty, who have been meeting in Bratislava, Slovakia, for the past fortnight to discuss progress.But why should we care? Why should it matter if any of these small obscure things disappears? What if they have no obvious use?The last question ignites Dr Walter. “Conservationists are pushed into the corner by the media and the development community to prove that something is useful, otherwise, they say, we’re going to get rid of it. It’s completely the wrong question.”My response when people say, prove it’s useful, is to say, prove to me it’s not.”With the technology of 50 years ago we would have missed taxol and vincristine, which are both anti-cancer drugs that come from plants. But now he has become responsible for the plant itself, journeying to the island to study it once a year with his colleague, Steve Compton from the University of Leeds. (They live in a hut at the foot of the lighthouse.) He describes it: “Three feet tall with great big yellow heads, looks like oil seed rape but grows out of sea cliffs, a big bulky plant with a lot of architecture, and you would think it would get smashed to bits by the wind but it doesn’t Why it’s there is a mystery. Its friends and relatives are all down in the Iberian peninsula. The cabbage population goes up and down like a yo-yo,” he explains, “and when anything does that, there’s always the possibility that the string will break when it’s at the bottom.”What are we doing about the threats? In Britain, quite a lot.

Roger Key defends the Lundy cabbage, a bright yellow flower that covers the cliffs of the island and occurs nowhere else. Short, bearded, long-haired, bespectacled and enthusiastic, Dr Key is an insect specialist at English Nature’s Peterborough headquarters, and his first love was the bronze Lundy cabbage flea beetle, which livesin the Lundy cabbage. And then he will tell you, with more concern in his voice, of the worries about the most threatened ones, the round-leaved eyebright, Euphrasia rotundifolia, down to one clifftop site in north- west Scotland, and the Cornish eyebright, Euphrasia vigursii, which has vanished from many of its sites in the past 10 years.All these plants have their defenders. He will tell you that Euphrasia heslop-harrisonii was named after JW Heslop-Harrison, professor of botany at the University of Newcastle in the post-war years, and that Euphrasia campbelliae was named after Miss Maybud Campbell, a Scottish botanist of the early part of the century who discovered it in its sole location, the island of Lewis. He explains that eyebrights are a genus whose members find it easy to interbreed, so some of these British rarities are new species that have evolved by hybridisation.

But the more you go into it, the more fascinating it becomes, for the plants themselves and for the people who are studying and protecting them.The eyebrights – six of them in the list – are a good example. The man who can tell you about them is Dr Alan Silverside, lecturer in plant ecology at the University of Paisley near Glasgow. He will tell you that the Dwarf Welsh eyebright is found on Snowdon and Cader Idris, but the Snowdon eyebright Euphrasia rivularis was badly named in English by the great plant illustrator W Keble Martin because it is found in the Lake District as well as Snowdonia. And a fourth, Interrupted brome, Bromus interruptus, did finally become extinct in the wild in 1972, despite the efforts of conservationists in Cambridgeshire to save it.It is at first sight an obscure list, and the majority of the species will not be found in the sort of pocket guide to wild flowers you can pick up in a bookshop, unless in some of the footnotes. A third, the Killarney fern, Trichomanes speciosum, was nearly driven to extinction by Victorian fern-collectors avid to possess its diaphanous evergreen fronds. They have evolved through hybridisation with other species, or through isolation in a particular habitat, then found an ecological niche and clung on to it, and, in some cases, evolution can still be observed taking place. Another – the Lundy cabbage, Coincya wrightii – seems to be a strange Ice-Age survivor on its island in the Bristol channel.

One – the Welsh groundsel, Senecio cambrensis – evolved independently in two separate places, Wrexham and Edinburgh docks, only the second occasion this is ever known to have happened. But there are also thousands of examples of less, shall we say, theatrical plants that are imperilled, and 19 of them, including the dwarf Welsh eyebright, are from Britain.What are they, these bits of the world’s threatened flora that we have in our care? Sixteen of them are endemic – they occur in Britain and nowhere else. We are way out.”Some of the 33,798 are themselves what might be termed charismatic megaflora, once you can decipher the scientific names – magnificent ornamentals such as the Cilician cyclamen from Turkey, whose flowers are pale pink with deep carmine and magenta blotches, and which has been persecuted by collectors, or the bright-yellow Drury’s orchid from Kerala in India, which is threatened by forest fires. Obviously, it’s going to cost more to conserve animal than plant species, but there’s no way you can justify 97-3. No one has counted the beetle species in the canopy of the Amazon rainforest. But when the Red List of Threatened Animals was published by the World Conservation Union in 1996, it listed 5,205 species thought to be in various degrees of danger. When the Red List of Threatened Plants was published on April 8 this year, it listed 33,798 flowers, trees, grasses and ferns thought to be imperilled, out of a world total estimated at 270,000.”I’m not saying we know all the plants that should be in the book,” says Dr Walter, a softly-spoken botanist from Michigan, “but between six and seven times as many plants as animals are threatened, and, according to US figures, 97 cents of every conservation dollar are spent on animals, and three on plants It’s an unbelievable disparity.