And up to where the rare lily lives

IT IS tiny, yellow and lovely, and perhaps Britain's most inaccessible wildflower. To pick it, you'd have to know where it was, and then you'd have to be a rock climber. Yet the rare Snowdon Lily is still threatened.

If and when global warming comes to Britain, it is likely to be among the first wildflower casualties: the minute alpine bloom, which flourishes only in cold, hostile conditions where it can hold its own against competitors, will be forced higher up the flanks of its mountain namesake to seek out cooler air.

But, as the temperature rises, there will come a time when it is confined to the highest cliffs and can retreat no further skywards. The Snowdon Lily will run out of mountain.

Pondering this future every year is Barbara Jones, a keen climber and botanist, who is an expert on Lloydia serotina, named after the 17th-century botanist Edward Lloyd. Ms Jones became intrigued and charmed by the lily after being introduced to it a dozen years ago and has now made it the subject of her PhD thesis.

The plant is found at less than a dozen locations in Snowdonia National Park, north-west Wales, usually on cold, dark slopes such as north-east facing cliffs, many of them inaccessible without climbing gear and experience.

Ms Jones has both, and this is her busiest time of year, when the lily puts out its delicate creamy yellow flower for a few weeks - six petals with a diameter a little larger than a 1p piece.

She spends hours slowly abseiling down cliff faces, pausing to count the plants and record their location, vigour and the physical and chemical conditions they live in. When it is not flowering, the lily looks just like grass - a few whiskery blades poking from cracks in the rocks.

The lily grows on mountains around the northern hemisphere, but in Britain it is clinging on by its fingertips. It is slow-growing, with five years elapsing from seed germination to first flowering, and seems to produce few successful seeds.

Its distribution in Britain is a mystery. No one knows why it is found only in Snowdonia and not in higher and colder mountains like the Cairngorms, where incidentally it might have a better chance of surviving global warming. The British population probably suffers from a lack of genetic variation, which further reduces its ability to cope with a warming climate.

Although there may be several thousand plants left in Snowdonia, many will be clones of each other because the lily often reproduces vegetatively rather than sexually, growing rhizomes which become new plants. It emerges from a tiny bud each spring with the leaves and flower dying back for the winter.

''This is a relict population and I'd like to find out if it's stable, falling or growing,'' says Ms Jones, who is taking three years' unpaid leave from her job with the Countryside Council for Wales to study the lily.

Victorian plant collectors and then the high-altitude grazing of sheep have pushed Lloydia to the brink. It has been illegal to pick flowers or collect specimens for decades, but there is little sign of a comeback.

Last weekend, near the base of a great cliff, Ms Jones was monitoring the plants at one of the lily's last two strongholds. Her passion for it gives her a certain possessiveness; she talks of ''my plants''. Some of her monitoring is done in midwinter, when the rocks are covered in ice and snow. You would have to be wicked and crass to snatch the lily - and extremely nimble to escape her if she caught you in the act.

Some of the attraction seems to be born out of sympathy for one of nature's underdogs. ''Most alpine plants keep low down on the rocks and stay tiny in order to seek shelter,'' she says.

''Yet here's this daft thing sticking its flower and long leaves out into the cold and wind.''