at least one out of every eight known plant species on the Earth is threatened with exinction or nearly extinct, says the first international survey of plant diversity. Sixteen organisations have jointly worked for 20 years to complete the study. Habitat destruction and introduction of nonnative species have caused about 34,000 species to become so rare that they could easily disappear, says the study. It is nearly 12.5 per cent of the 2,70,000 fern, conifer and flowering species known worldwide.

In the us , nearly 29 per cent of 16,000 species are at risk. Similar per centages have been recorded for Australia and South Africa. Some of the cases are really noteworthy. For instance, 75 per cent of the yew family