According to new research, three-quarters of all the threatened species have no legal protection.

The most threatened tree species in the UK are all inter-related.

Each tree is a clone of another.

BBC environment correspondent Robert Pigott reports

Anyone concerned about genetic engineering can relax - these are not products of some geneticist's laboratory.

Instead, they exist because of a natural creative process dating back to the ice age.

The trees known as whitebeams are very good at reproducing, but not so clever when it comes to moving around and colonising areas.

Because they are copies of their parents they cannot adapt to changing circumstances and locations.

One of only 16 Leys Whitebeams in the world

All 11 UK tree species on the list published by the World Wide Fund for Nature, are from the Sorbus group.

One such species is the highly rare Ley's Whitebeam, which can only be found in the wild on one hillside in the Brecon Beacons, in Wales.

There are just 16 examples left of this tree, which was probably created shortly after the last ice age, when the Rowan tree and the Rock Whitebeam reproduced.

The Rowan and the Rock Whitebeam bred together.....

Ray Woods, from the Countryside Council For Wales, calls it "slightly fertile," since it spreads seeds which are identical clones to the mother plant.

He said: "Leys Whitebeam has found a way of asexual reproduction. None of the pollen that it produces is good at all, but it's managed to find a way.

.... to form the Leys Whitebeam

"But all its offspring are identical to the parent tree, so its not well adapted to change."

Nature is not the only reason though - man does not help either.

According to the World Conservation Monitoring Centre's Website showing the full list of trees, quarrying has destroyed some of the sites the species did manage to colonise nearby.

The BBC's Richard Wilson in the Avon gorge where whitebeams are surviving

Another endangered species is Sorbus Wilmottiana - or Wilmott's Whitebeam - with only 20 examples managing to live on in the Avon Gorge, where three of the other ten species can also be found including the Bristol variety, whose numbers are slowly growing.

However the Wilmott's variety is causing greater concern. The new World List says there have been recent reports of the illegal collection and cutting down of trees in the gorge, despite attempts to protect the species.

Tony Robinson from English Nature, who works in the area, told BBC Radio 4's Today programme that the whitebeams are actually very good at forming new species.

But it is then that their problems start.

"The Whitebeams are very much trees of open space - rock faces and open slopes.

"Most people know Mountain Ash which is actually a member of the same group as the whitebeams and this grows in very open, mountainous spaces."

He also explained how they can be protected: "What we're trying to do here in the Avon gorge is retain the open spaces, the rocky open cliffs and slopes."

The UK's threatened trees

The areas featured here - the Brecon Beacons and the Avon Gorge near Bristol - are home to over half the 11 threatened species in the UK.

In fact the south west of Britain is where you can find eight of them.

Only two are in Scotland - on the remote island of Arran, and just one in northern England.

• Sorbus wilmottiana: 20 trees in Avon Gorge where the area is managed so as to conserve the rare plants.

• Sorbus bristoliensis (Bristol Whitebeam): 100 also found in Avon Gorge, where numbers are increasing.

• Sorbus anglica: 600 left. Found in Avon Gorge, but also Devon, north Somerset, the Wye Valley, Shropshire, Brecon, Montgomery, Denbigh and Kerry.

• Sorbus eminens: 250 found mostly in Avon Gorge, but also Somerset, the Wye Valley, and Bangor in North Wale.

• Sorbus subcuneata: Found along Devon and Somerset coasts, but population at Minehead threatened.

• Sorbus vexans: Found along small part of Devon and Somerset coast.

• Sorbus leyana (the Leys Whitebeam): 20 trees known at two sites in Brecon Beacons. 16 are in the wild (pictured above).

• Sorbus leptophylla: 44 at last count. Also in Brecon Beacons.

• Sorbus lancastriensis: Morecambe Bay, Lancashire.

• Sorbus pseudofennica: 500 left on Scotland's Isle of Arran.

• Sorbus arranensis: 500 left in northern Arran.