By Alex Kirby BBC News Online environment correspondent

Encephalartos woodii Photo: JS Donaldson

Cycads, plants resembling palms, first appeared in the fossil record about 300 million years ago.

But today they face a risk of extinction four times greater than the average for plants.

One of the worst threats comes from the trade in wild plants for the horticultural trade.

The plight of the cycads, which are found in Asia, Africa, Australia and the Americas, is described in a report by IUCN-The World Conservation Union.

The report, Cycad Status Survey And Conservation Action Plan, was prepared by the cycad specialist group of IUCN's species survival commission.

Demand from landscapers

There are about 297 cycad species and sub-species, varying from small plants found beneath the forest canopy to tall ones growing in the canopy itself or out in the open.

Despite their venerable lineage, the report says, 53% of all cycads are threatened with extinction, compared with an average 12.5% for plants in general.

Bowenia spectabilis in the rainforests of northern Queensland, Australia Photo: JS Donaldson

Two species are already extinct in the wild, and IUCN says the pressures of modern lifestyles suggest more are likely to follow suit.

It says the main threats include habitat destruction for farming, mining and urban development, traditional use, both for medicine and magic, and invasive plant species.

And the collection of plants and seeds from the wild for horticulture is high on the list.

The report says the demand for large cycads from landscapers means a high risk of mature plants being taken straight from the wild.

So there is more need for cultivated plants to supply a legal trade and lessen the pressure on the wild stocks.

Plant passports

Technology means it is becoming easier to tell wild from cultivated cycads.

In South Africa, individual plants are being microchipped with a unique number which is entered on a national register to trace their movements, and DNA techniques are also helping to trace the parentage of plants in trade.

Cycads are slow-growing dioecious plants (ones with separate male and female forms), which reproduce infrequently and depend on specialist pollinators.

This means that individual plants need to be close together for pollination and reproduction to occur.

Some species, like the Albany cycad, depend for their survival in the wild on artificial pollination, because the specialist beetles which used to pollinate the plants no longer exist.

For others the only hope now may be conservation in botanical gardens and seed banks.

The cycad specialist group is chaired by Dr John Donaldson.

He says: "Cycads experience the same problems that many other plant species face, but their biology makes them more vulnerable to human-induced disturbance."