A tiny difference

Along the road to the mountain, bare twigs of blackthorn sparkle with white blossom - "flowers without leaves like easter snow, hailstones clustering at dayligone" in one of Michael Longley's new poems, The Weather in Japan (the lovely Scots word for dusk is a gift in passing).

Flowers that jump the gun like this have a special, declarative beauty. Down in the dunes just now, coltsfoot has rushed up its flower-buds from under the sand, anxious to light a brief flare of gold and get its seeds launched on the wind.

It's a much bleaker scene on the machair, the close-cropped, wet and mossy plain that separates the dunes from farmland. But even here, things are happening, if you know where to look. Michael Longley once described how this landscape first intimidated him with the hugeness of mountains, sea and sky, then forced him down "on my knees, taking it all in".

"All" has often meant a flower: the tiny spiral of bells on a little autumn orchid, lady's tresses, or the chaste white buttercup of Grass of Parnassus, a green-veined chalice in the vastness of the machair. But what would Longley make, I wonder, of a plant so small that even a botanist has to learn to see it, and whose miniature rosette, like an exquisite lettuce, is best enjoyed under a microscope?

Petalwort, otherwise Petalophyllum ralfsii, is a liverwort, a class of "lower" plants, like mosses and lichens. Just now, under the lens, there are silvery stalks pushing up between the bright, translucent green wings of the male plants, each with its canister of spores. In the moistness of March, its colonies show up in green mats, but a hot, dry summer can send the plants shrinking underground into a network of tubers - "aestivating", just like earthworms do.

I could have lived on happily without a close encounter with petalwort, if it had not been elected such a rarity. It has been listed on Appendix 1 of the Bern Convention and Annex II of the EU Habitats Directive, which means that wherever it grows must be protected as a Special Area of Conservation. It was also among the four rare liverworts and 14 rare mosses named last year in Ireland in a special Flora Protection Order.

The irony is that, while indeed rare and threatened in most European countries, petalwort thrives in quite unprecedented numbers - by the million, in places - in the special conditions of Connacht's most overgrazed coastal machairs.

Petalophyllum is adapted to quite a narrow niche in nature. It likes the high calcium levels of freshly-blown shell sand, frequently flushed with water. And it dislikes competition from other vegetation. Typically, it finds these conditions around the edges of damp dune slacks and often along dune paths where trampling keeps taller plants in check.

It has travelled quite widely, its spores blown in the wind or carried on the muddy feet of birds. It grows around the Mediterranean, including north Africa and Turkey, and on Atlantic shores from Portugal to the north-west of Scotland. It has even reached the southern USA.

But despite this wide scattering, its actual populations are small and few, and many have been lost to the spread of golfcourses and other sand-dune developments. At most of the sites left in Britain, the plants are few enough to be counted individually - and they all add up to less than 100,000. Once Europe listed petalwort in such an urgent way, along with better-known rarities such as the Killarney fern, Duchas needed to map its distribution. Dr Neil Lockhart carried out widespread searches, and a British botanist, D. T. Holyoak, came in to help. What they found last spring on the intensively-grazed machairs of Mayo and Galway were expanses of Petalophyllum that are possibly unique in the world.

Here at Thallabawn, in a wide strip along the base of machair slopes, are at least 150,000 plants - more than Britain's entire total. At Garter Hill beside Carrowteige in North Mayo, the colonies are estimated at 1.6 million plants. And on the heavily-grazed commonage of the Slyne Head peninsula, Co Galway, where just one square metre might hold 200-300 petalwort plants, the total population reaches a startling estimate of about 5.5 million.

It is, of course, a freak circumstance. Left to nature, Petalophyllum would be an unobtrusive coloniser at the margins of sand-dune vegetation, growing mostly in a few hundreds of closely-cloned plants. Human disturbance, by destroying its habitats, has made it a rarity over most of its range. But abuse of other habitats, through overgrazing, has now turned its natural ecology on its head. Only in the west of Ireland, with its distinctive regime of rainfall and humidity and a special landform - the machair - could this have happened.

What does this do to its "rarity"? Nothing very much, actually, since a few more golf courses and caravan parks could make quick work of these exceptional colonies among the 18 Irish petalwort sites. That won't happen (and certainly not now) at the places I have named, but a plant as choosy as this one does pose problems for conservation.

Machair vegetation of the flowering kind is rich, diverse and beautiful - or would be, if the sheep ever let it bloom. Cut down on the sheep and petalwort could diminish. Put a fence round the petalwort and it is choked out by taller plants. All one can do, really, is to let it take its chances, ebbing and flowing within a reasonable management of change. What matters is to sustain the natural dune dynamics, so that all the special plants and plant-associations get a good chance to survive.

Why should we care about a plant that few human beings will ever actually see? Even if its precise form, its stemless whorls of green wings, is unique in our flora, is it worth all this fuss - all these costly person-hours invested by botanists, down on their knees on fertiliser sacks, counting with a finger-nail?

The loss of species, of biodiversity, is a degradation of the planet from one human generation to the next. A "rare" species often speaks for a vanishing habitat - the grouse that calls for the heatherless hills, the Ice Age snail for a marsh drained and built on. We often cheat about the rarities that move us, insisting that they charm us in some way. Petalwort is actually quite beautiful, lit in a fiber-optic glow - trust me.

Michael Longley's new collection, The Weather in Japan, is published by Cape Poetry, price £8 in the UK