Take a good look at the plants on these pages: you may never see some of them in the wild again. Nineteen British plants feature on a list of 34,000 facing global extinction. Should we care about the Lundy cabbage? The Snowdon eyebright? The Jersey pink? Yes, yes, yes, says Michael McCarthy
It's a long way from the African elephant to the dwarf Welsh eyebright, and not just in size (12ft tall for Loxodonta africana, an inch or so for Euphrasia cambrica). There is an even bigger disparity in the way we perceive them. Who could remain unaffected by the massive elephant slaughter of the Eighties, as ivory poachers left a bloody trail across Africa? Great beasts, noble beasts, whole family groups of them, shot down, tusks hacked out, and in shocking pictures on the TV screens. The world acted: in 1989, the international ivory trade was outlawed.

But what is this wee thing down in the short-grazed turf on the slopes of Snowdon? Minute. You can hardly see it. Is that it there? Tiny white- buff flowers, one of those little fiddly weeds that looks like a dozen others - does it really matter if that disappears, as the elephants might, and as the rhinos and the tigers nearly have? Does it matter if it vanishes from Snowdon? From Wales? From the earth?

There is an increasingly audible Yes. The African elephant is a prime example of what thinking conservationists now term, with a certain irritation, "charismatic megafauna": big, highly visible animals and birds that excite in human beings favourable emotions such as awe, admiration or tenderness. The giant panda heads the list, of course, and sits there in the logo of the World Wide Fund for Nature, cute, cuddly and alone. They're not stupid at WWF: it is a marvellous animal, no effort should be spared to save it, and it attracts attention at once. The trouble with charismatic megafauna, though, is that it can attract too much attention, and too much concern, and eventually too much conservation effort and funding, at the expense of everything else. And everything else matters.

Take plants. Plants underscore our world, not only shaping the landscape, but sitting at the bottom of the food chain, converting sunlight into things that can be eaten. All human civilisation depends on hybrid forms of between 20 and 50 plants - 30 is a good guess - such as rice and wheat and potatoes. "Without them," says Kerry Walter of the Royal Botanic Garden, Edinburgh, "we are nothing. We die. We have no civilisation. These are the most important assets we have."

Yet public awareness of the worldwide extinction threat to plants is nowhere near that of the threat to animals. Perhaps that is why such an international stir was created last month when Dr Walter and his colleague Harriet Gillett from the World Conservation Monitoring Centre at Cambridge unveiled the survey they have edited - the first - of the world's endangered plants, and showed that the figure was more than one in eight.

Animal species - meaning mammals, birds, fishes, reptiles, insects, everything that moves under its own steam - may total a million, or may be as many again. 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. Obviously, it's going to cost more to conserve animal than plant species, but there's no way you can justify 97-3. 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. 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. 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. 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. Another - the Lundy cabbage, Coincya wrightii - seems to be a strange Ice-Age survivor on its island in the Bristol channel. A third, the Killarney fern, Trichomanes speciosum, was nearly driven to extinction by Victorian fern-collectors avid to possess its diaphanous evergreen fronds. 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. 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 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. 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. 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. 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. 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 lives

in the Lundy cabbage. 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. As part of its responsibilities in signing the world's first comprehensive wildlife protection treaty, the Convention on Biodiversity, at the Earth Summit in Rio de Janeiro in 1992, the government in 1994 published a formal biodiversity action plan. It followed this up in 1995 with specific schemes to save 116 plants and animals. 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. [Taxol comes from yew species and vincristine from the rosy periwinkle of Madagascar.] We didn't know back then how to extract such chemicals, and we would have made a conservation decision that neither of these plants had a use and perhaps dropped them. But we can't predict what people are going to know."

However, he offers a much broader and more arresting argument in defence of letting nothing slip to extinction. "On the day of the launch last month [of the list of threatened plants] it was announced that a fault had been found in a single part in Boeing 747s that might have caused the planes to crash. We've got 270,00 kinds of plants on earth. Think of them as 270,00 dismantled parts sitting on the runway, and we've got 34,000 of them in the corner which are rusted, say, or we don't know where they go or how they fit in, so we just throw them out. We'll rebuild the plane without them.

"Are you going to get on that plane? Of course not. The fact that something is back in the tail section - it's some grass in Bhutan - and is of no interest to us up in first class, in the UK, say, doesn't make it any less important. We just don't know about the 34,000. Boeing would be able to tell you that this or that is a redundant part because they've got a user's manual. But we can't do that with plants. We don't have a user's manual for the earth."

And were we to have one, of course - in a short paragraph befitting its status as a piece of inconspicuous miniflora, but there nonetheless - the dwarf Welsh eyebright would be in it

Captions: Killarney fern Trichomanes speciosum (above) Nearly collected to extinction by Victorian plant hunters but clinging on in damp places along western coasts.

Interrupted brome Bromus interruptus (opposite) A grass of arable fields now extinct in the wild. Last seen at Pampisford, Cambs, 1972.

From top: English sandwort

Arenaria norvegica anglica. Found only on the slopes of Ingleborough mountain in North Yorkshire.

Lundy cabbage

Coincya wrightii A possible Ice-Age survival that brightens the cliffs of the island in the Bristol Channel and occurs nowhere else.

Western ramping fumitory Fumaria occidentalis A showy plant that climbs over hedges and walls in Cornwall with flowers that change from white to pink.

Rock sea lavender Limonium recurvum A rare subspecies of a commoner clifftop flower, first identified between the wars on the tip of Portland Bill in Dorset.

Jersey pink Dianthus gallicus (above)

A beautiful wild carnation growing on sand dunes in Jersey as well as in France and Spain.

Mountain scurvy grass Cochlearia micacea (left) A rarity of the Scottish highlands and a relative of a commoner plant that was once thought to cure scurvy.

Clockwise from right:

Dwarf Welsh eyebright Euphrasia cambrica

A tiny plant restricted to patches of cropped turf on Snowdon and surrounding peaks, and on Cader Idris further south. Probably depended on sheep grazing.

Heslop-Harrison's eyebright Euphrasia heslop-harrisonii

A flower of turf in salt marshes on the edge of sheltered sea lochs on the north-west coast of Scotland. Named after a professor of botany at Newcastle University.

Snowdon eyebright Euphrasia rivularis A misnomer in English because it is found in the Lake District as well as in North Wales. Covers wet rock ledges and mountain streams.

Cornish eyebright Euphrasia vigursii An increasing rarity with its purple rather than white flowers. Restricted to damp heathland on the Devon and Cornish coasts but has vanished from many former sites.

Shore dock Rumex rupestris (right) A plant that needs fresh water at the base of sea cliffs; only a few places are suitable, mainly in southern Cornwall

Coastal little robin Geranium purpureum forsteri (far right) Found only on the shore of the Solent, a maritime version of little robin, itself a rarity.

The full list of 19 globally threatened plant species which occur in Britain is:

1) English sandwort Arenaria norvegica anglica; 2) Interrupted brome Bromus interruptus; 3) Scottish small reed Calamagrostris scotica; 4) Mountain scurvy grass Cochlearia micacea; 5) Lundy cabbage Coincya wrightii; 6) Jersey pink Dianthus gallicus; 7) Western ramping fumitory Fumaria occidentalis; 8) Coastal little robin Geranium purpureum forsteri; 9) Rock sea lavender Limonium recurvum; 10) Shore dock Rumex rupestris; 11) Welsh groundsel Senecio cambrensis; 12) Arran whitebeam Sorbus arranensis; 13) Killarney fern Trichomanes speciosum; 14) Dwarf Welsh eyebright Euphrasia cambrica; 15) Snowdon eyebright Euphrasia rivularis; 16) Campbell's Eyebright Euphrasia campbelliae; 17) Heslop-Harrison's eyebright Euphrasia heslop-harrisonii; 18) Round-leaved eyebright Euphrasia rotundifolia; 19) Cornish eyebright Euphrasia vigursii.